Skip to content
This repository
tree: 357e288f44
Fetching contributors…

Octocat-spinner-32-eaf2f5

Cannot retrieve contributors at this time

file 1605 lines (1572 sloc) 87.476 kb
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651 652 653 654 655 656 657 658 659 660 661 662 663 664 665 666 667 668 669 670 671 672 673 674 675 676 677 678 679 680 681 682 683 684 685 686 687 688 689 690 691 692 693 694 695 696 697 698 699 700 701 702 703 704 705 706 707 708 709 710 711 712 713 714 715 716 717 718 719 720 721 722 723 724 725 726 727 728 729 730 731 732 733 734 735 736 737 738 739 740 741 742 743 744 745 746 747 748 749 750 751 752 753 754 755 756 757 758 759 760 761 762 763 764 765 766 767 768 769 770 771 772 773 774 775 776 777 778 779 780 781 782 783 784 785 786 787 788 789 790 791 792 793 794 795 796 797 798 799 800 801 802 803 804 805 806 807 808 809 810 811 812 813 814 815 816 817 818 819 820 821 822 823 824 825 826 827 828 829 830 831 832 833 834 835 836 837 838 839 840 841 842 843 844 845 846 847 848 849 850 851 852 853 854 855 856 857 858 859 860 861 862 863 864 865 866 867 868 869 870 871 872 873 874 875 876 877 878 879 880 881 882 883 884 885 886 887 888 889 890 891 892 893 894 895 896 897 898 899 900 901 902 903 904 905 906 907 908 909 910 911 912 913 914 915 916 917 918 919 920 921 922 923 924 925 926 927 928 929 930 931 932 933 934 935 936 937 938 939 940 941 942 943 944 945 946 947 948 949 950 951 952 953 954 955 956 957 958 959 960 961 962 963 964 965 966 967 968 969 970 971 972 973 974 975 976 977 978 979 980 981 982 983 984 985 986 987 988 989 990 991 992 993 994 995 996 997 998 999 1000 1001 1002 1003 1004 1005 1006 1007 1008 1009 1010 1011 1012 1013 1014 1015 1016 1017 1018 1019 1020 1021 1022 1023 1024 1025 1026 1027 1028 1029 1030 1031 1032 1033 1034 1035 1036 1037 1038 1039 1040 1041 1042 1043 1044 1045 1046 1047 1048 1049 1050 1051 1052 1053 1054 1055 1056 1057 1058 1059 1060 1061 1062 1063 1064 1065 1066 1067 1068 1069 1070 1071 1072 1073 1074 1075 1076 1077 1078 1079 1080 1081 1082 1083 1084 1085 1086 1087 1088 1089 1090 1091 1092 1093 1094 1095 1096 1097 1098 1099 1100 1101 1102 1103 1104 1105 1106 1107 1108 1109 1110 1111 1112 1113 1114 1115 1116 1117 1118 1119 1120 1121 1122 1123 1124 1125 1126 1127 1128 1129 1130 1131 1132 1133 1134 1135 1136 1137 1138 1139 1140 1141 1142 1143 1144 1145 1146 1147 1148 1149 1150 1151 1152 1153 1154 1155 1156 1157 1158 1159 1160 1161 1162 1163 1164 1165 1166 1167 1168 1169 1170 1171 1172 1173 1174 1175 1176 1177 1178 1179 1180 1181 1182 1183 1184 1185 1186 1187 1188 1189 1190 1191 1192 1193 1194 1195 1196 1197 1198 1199 1200 1201 1202 1203 1204 1205 1206 1207 1208 1209 1210 1211 1212 1213 1214 1215 1216 1217 1218 1219 1220 1221 1222 1223 1224 1225 1226 1227 1228 1229 1230 1231 1232 1233 1234 1235 1236 1237 1238 1239 1240 1241 1242 1243 1244 1245 1246 1247 1248 1249 1250 1251 1252 1253 1254 1255 1256 1257 1258 1259 1260 1261 1262 1263 1264 1265 1266 1267 1268 1269 1270 1271 1272 1273 1274 1275 1276 1277 1278 1279 1280 1281 1282 1283 1284 1285 1286 1287 1288 1289 1290 1291 1292 1293 1294 1295 1296 1297 1298 1299 1300 1301 1302 1303 1304 1305 1306 1307 1308 1309 1310 1311 1312 1313 1314 1315 1316 1317 1318 1319 1320 1321 1322 1323 1324 1325 1326 1327 1328 1329 1330 1331 1332 1333 1334 1335 1336 1337 1338 1339 1340 1341 1342 1343 1344 1345 1346 1347 1348 1349 1350 1351 1352 1353 1354 1355 1356 1357 1358 1359 1360 1361 1362 1363 1364 1365 1366 1367 1368 1369 1370 1371 1372 1373 1374 1375 1376 1377 1378 1379 1380 1381 1382 1383 1384 1385 1386 1387 1388 1389 1390 1391 1392 1393 1394 1395 1396 1397 1398 1399 1400 1401 1402 1403 1404 1405 1406 1407 1408 1409 1410 1411 1412 1413 1414 1415 1416 1417 1418 1419 1420 1421 1422 1423 1424 1425 1426 1427 1428 1429 1430 1431 1432 1433 1434 1435 1436 1437 1438 1439 1440 1441 1442 1443 1444 1445 1446 1447 1448 1449 1450 1451 1452 1453 1454 1455 1456 1457 1458 1459 1460 1461 1462 1463 1464 1465 1466 1467 1468 1469 1470 1471 1472 1473 1474 1475 1476 1477 1478 1479 1480 1481 1482 1483 1484 1485 1486 1487 1488 1489 1490 1491 1492 1493 1494 1495 1496 1497 1498 1499 1500 1501 1502 1503 1504 1505 1506 1507 1508 1509 1510 1511 1512 1513 1514 1515 1516 1517 1518 1519 1520 1521 1522 1523 1524 1525 1526 1527 1528 1529 1530 1531 1532 1533 1534 1535 1536 1537 1538 1539 1540 1541 1542 1543 1544 1545 1546 1547 1548 1549 1550 1551 1552 1553 1554 1555 1556 1557 1558 1559 1560 1561 1562 1563 1564 1565 1566 1567 1568 1569 1570 1571 1572 1573 1574 1575 1576 1577 1578 1579 1580 1581 1582 1583 1584 1585 1586 1587 1588 1589 1590 1591 1592 1593 1594 1595 1596 1597 1598 1599 1600 1601 1602 1603 1604
require 'active_support/core_ext/array/wrap'
require 'active_support/core_ext/enumerable'
require 'active_support/core_ext/module/delegation'
require 'active_support/core_ext/object/blank'
require 'active_support/core_ext/string/conversions'
require 'active_support/core_ext/module/remove_method'
require 'active_support/core_ext/class/attribute'

module ActiveRecord
  class InverseOfAssociationNotFoundError < ActiveRecordError #:nodoc:
    def initialize(reflection, associated_class = nil)
      super("Could not find the inverse association for #{reflection.name} (#{reflection.options[:inverse_of].inspect} in #{associated_class.nil? ? reflection.class_name : associated_class.name})")
    end
  end

  class HasManyThroughAssociationNotFoundError < ActiveRecordError #:nodoc:
    def initialize(owner_class_name, reflection)
      super("Could not find the association #{reflection.options[:through].inspect} in model #{owner_class_name}")
    end
  end

  class HasManyThroughAssociationPolymorphicSourceError < ActiveRecordError #:nodoc:
    def initialize(owner_class_name, reflection, source_reflection)
      super("Cannot have a has_many :through association '#{owner_class_name}##{reflection.name}' on the polymorphic object '#{source_reflection.class_name}##{source_reflection.name}'.")
    end
  end

  class HasManyThroughAssociationPolymorphicThroughError < ActiveRecordError #:nodoc:
    def initialize(owner_class_name, reflection)
      super("Cannot have a has_many :through association '#{owner_class_name}##{reflection.name}' which goes through the polymorphic association '#{owner_class_name}##{reflection.through_reflection.name}'.")
    end
  end

  class HasManyThroughAssociationPointlessSourceTypeError < ActiveRecordError #:nodoc:
    def initialize(owner_class_name, reflection, source_reflection)
      super("Cannot have a has_many :through association '#{owner_class_name}##{reflection.name}' with a :source_type option if the '#{reflection.through_reflection.class_name}##{source_reflection.name}' is not polymorphic. Try removing :source_type on your association.")
    end
  end

  class HasOneThroughCantAssociateThroughCollection < ActiveRecordError #:nodoc:
    def initialize(owner_class_name, reflection, through_reflection)
      super("Cannot have a has_one :through association '#{owner_class_name}##{reflection.name}' where the :through association '#{owner_class_name}##{through_reflection.name}' is a collection. Specify a has_one or belongs_to association in the :through option instead.")
    end
  end

  class HasManyThroughSourceAssociationNotFoundError < ActiveRecordError #:nodoc:
    def initialize(reflection)
      through_reflection = reflection.through_reflection
      source_reflection_names = reflection.source_reflection_names
      source_associations = reflection.through_reflection.klass.reflect_on_all_associations.collect { |a| a.name.inspect }
      super("Could not find the source association(s) #{source_reflection_names.collect{ |a| a.inspect }.to_sentence(:two_words_connector => ' or ', :last_word_connector => ', or ', :locale => :en)} in model #{through_reflection.klass}. Try 'has_many #{reflection.name.inspect}, :through => #{through_reflection.name.inspect}, :source => <name>'. Is it one of #{source_associations.to_sentence(:two_words_connector => ' or ', :last_word_connector => ', or ', :locale => :en)}?")
    end
  end

  class HasManyThroughCantAssociateThroughHasOneOrManyReflection < ActiveRecordError #:nodoc:
    def initialize(owner, reflection)
      super("Cannot modify association '#{owner.class.name}##{reflection.name}' because the source reflection class '#{reflection.source_reflection.class_name}' is associated to '#{reflection.through_reflection.class_name}' via :#{reflection.source_reflection.macro}.")
    end
  end

  class HasManyThroughCantAssociateNewRecords < ActiveRecordError #:nodoc:
    def initialize(owner, reflection)
      super("Cannot associate new records through '#{owner.class.name}##{reflection.name}' on '#{reflection.source_reflection.class_name rescue nil}##{reflection.source_reflection.name rescue nil}'. Both records must have an id in order to create the has_many :through record associating them.")
    end
  end

  class HasManyThroughCantDissociateNewRecords < ActiveRecordError #:nodoc:
    def initialize(owner, reflection)
      super("Cannot dissociate new records through '#{owner.class.name}##{reflection.name}' on '#{reflection.source_reflection.class_name rescue nil}##{reflection.source_reflection.name rescue nil}'. Both records must have an id in order to delete the has_many :through record associating them.")
    end
  end

  class HasManyThroughNestedAssociationsAreReadonly < ActiveRecordError #:nodoc:
    def initialize(owner, reflection)
      super("Cannot modify association '#{owner.class.name}##{reflection.name}' because it goes through more than one other association.")
    end
  end

  class HasAndBelongsToManyAssociationForeignKeyNeeded < ActiveRecordError #:nodoc:
    def initialize(reflection)
      super("Cannot create self referential has_and_belongs_to_many association on '#{reflection.class_name rescue nil}##{reflection.name rescue nil}'. :association_foreign_key cannot be the same as the :foreign_key.")
    end
  end

  class EagerLoadPolymorphicError < ActiveRecordError #:nodoc:
    def initialize(reflection)
      super("Can not eagerly load the polymorphic association #{reflection.name.inspect}")
    end
  end

  class ReadOnlyAssociation < ActiveRecordError #:nodoc:
    def initialize(reflection)
      super("Can not add to a has_many :through association. Try adding to #{reflection.through_reflection.name.inspect}.")
    end
  end

  # This error is raised when trying to destroy a parent instance in N:1 or 1:1 associations
  # (has_many, has_one) when there is at least 1 child associated instance.
  # ex: if @project.tasks.size > 0, DeleteRestrictionError will be raised when trying to destroy @project
  class DeleteRestrictionError < ActiveRecordError #:nodoc:
    def initialize(name)
      super("Cannot delete record because of dependent #{name}")
    end
  end

  # See ActiveRecord::Associations::ClassMethods for documentation.
  module Associations # :nodoc:
    extend ActiveSupport::Concern

    # These classes will be loaded when associations are created.
    # So there is no need to eager load them.
    autoload :Association, 'active_record/associations/association'
    autoload :SingularAssociation, 'active_record/associations/singular_association'
    autoload :CollectionAssociation, 'active_record/associations/collection_association'
    autoload :CollectionProxy, 'active_record/associations/collection_proxy'

    autoload :BelongsToAssociation, 'active_record/associations/belongs_to_association'
    autoload :BelongsToPolymorphicAssociation, 'active_record/associations/belongs_to_polymorphic_association'
    autoload :HasAndBelongsToManyAssociation, 'active_record/associations/has_and_belongs_to_many_association'
    autoload :HasManyAssociation, 'active_record/associations/has_many_association'
    autoload :HasManyThroughAssociation, 'active_record/associations/has_many_through_association'
    autoload :HasOneAssociation, 'active_record/associations/has_one_association'
    autoload :HasOneThroughAssociation, 'active_record/associations/has_one_through_association'
    autoload :ThroughAssociation, 'active_record/associations/through_association'

    module Builder #:nodoc:
      autoload :Association, 'active_record/associations/builder/association'
      autoload :SingularAssociation, 'active_record/associations/builder/singular_association'
      autoload :CollectionAssociation, 'active_record/associations/builder/collection_association'

      autoload :BelongsTo, 'active_record/associations/builder/belongs_to'
      autoload :HasOne, 'active_record/associations/builder/has_one'
      autoload :HasMany, 'active_record/associations/builder/has_many'
      autoload :HasAndBelongsToMany, 'active_record/associations/builder/has_and_belongs_to_many'
    end

    autoload :Preloader, 'active_record/associations/preloader'
    autoload :JoinDependency, 'active_record/associations/join_dependency'
    autoload :AssociationScope, 'active_record/associations/association_scope'
    autoload :AliasTracker, 'active_record/associations/alias_tracker'
    autoload :JoinHelper, 'active_record/associations/join_helper'

    # Clears out the association cache.
    def clear_association_cache #:nodoc:
      @association_cache.clear if persisted?
    end

    # :nodoc:
    attr_reader :association_cache

    # Returns the association instance for the given name, instantiating it if it doesn't already exist
    def association(name) #:nodoc:
      association = association_instance_get(name)

      if association.nil?
        reflection = self.class.reflect_on_association(name)
        association = reflection.association_class.new(self, reflection)
        association_instance_set(name, association)
      end

      association
    end

    private
      # Returns the specified association instance if it responds to :loaded?, nil otherwise.
      def association_instance_get(name)
        @association_cache[name.to_sym]
      end

      # Set the specified association instance.
      def association_instance_set(name, association)
        @association_cache[name] = association
      end

    # Associations are a set of macro-like class methods for tying objects together through
    # foreign keys. They express relationships like "Project has one Project Manager"
    # or "Project belongs to a Portfolio". Each macro adds a number of methods to the
    # class which are specialized according to the collection or association symbol and the
    # options hash. It works much the same way as Ruby's own <tt>attr*</tt>
    # methods.
    #
    # class Project < ActiveRecord::Base
    # belongs_to :portfolio
    # has_one :project_manager
    # has_many :milestones
    # has_and_belongs_to_many :categories
    # end
    #
    # The project class now has the following methods (and more) to ease the traversal and
    # manipulation of its relationships:
    # * <tt>Project#portfolio, Project#portfolio=(portfolio), Project#portfolio.nil?</tt>
    # * <tt>Project#project_manager, Project#project_manager=(project_manager), Project#project_manager.nil?,</tt>
    # * <tt>Project#milestones.empty?, Project#milestones.size, Project#milestones, Project#milestones<<(milestone),</tt>
    # <tt>Project#milestones.delete(milestone), Project#milestones.find(milestone_id), Project#milestones.all(options),</tt>
    # <tt>Project#milestones.build, Project#milestones.create</tt>
    # * <tt>Project#categories.empty?, Project#categories.size, Project#categories, Project#categories<<(category1),</tt>
    # <tt>Project#categories.delete(category1)</tt>
    #
    # === Overriding generated methods
    #
    # Association methods are generated in a module that is included into the model class,
    # which allows you to easily override with your own methods and call the original
    # generated method with +super+. For example:
    #
    # class Car < ActiveRecord::Base
    # belongs_to :owner
    # belongs_to :old_owner
    # def owner=(new_owner)
    # self.old_owner = self.owner
    # super
    # end
    # end
    #
    # If your model class is <tt>Project</tt>, the module is
    # named <tt>Project::GeneratedFeatureMethods</tt>. The GeneratedFeatureMethods module is
    # included in the model class immediately after the (anonymous) generated attributes methods
    # module, meaning an association will override the methods for an attribute with the same name.
    #
    # === A word of warning
    #
    # Don't create associations that have the same name as instance methods of
    # <tt>ActiveRecord::Base</tt>. Since the association adds a method with that name to
    # its model, it will override the inherited method and break things.
    # For instance, +attributes+ and +connection+ would be bad choices for association names.
    #
    # == Auto-generated methods
    #
    # === Singular associations (one-to-one)
    # | | belongs_to |
    # generated methods | belongs_to | :polymorphic | has_one
    # ----------------------------------+------------+--------------+---------
    # other | X | X | X
    # other=(other) | X | X | X
    # build_other(attributes={}) | X | | X
    # create_other(attributes={}) | X | | X
    # create_other!(attributes={}) | X | | X
    #
    # ===Collection associations (one-to-many / many-to-many)
    # | | | has_many
    # generated methods | habtm | has_many | :through
    # ----------------------------------+-------+----------+----------
    # others | X | X | X
    # others=(other,other,...) | X | X | X
    # other_ids | X | X | X
    # other_ids=(id,id,...) | X | X | X
    # others<< | X | X | X
    # others.push | X | X | X
    # others.concat | X | X | X
    # others.build(attributes={}) | X | X | X
    # others.create(attributes={}) | X | X | X
    # others.create!(attributes={}) | X | X | X
    # others.size | X | X | X
    # others.length | X | X | X
    # others.count | X | X | X
    # others.sum(args*,&block) | X | X | X
    # others.empty? | X | X | X
    # others.clear | X | X | X
    # others.delete(other,other,...) | X | X | X
    # others.delete_all | X | X | X
    # others.destroy_all | X | X | X
    # others.find(*args) | X | X | X
    # others.exists? | X | X | X
    # others.uniq | X | X | X
    # others.reset | X | X | X
    #
    # == Cardinality and associations
    #
    # Active Record associations can be used to describe one-to-one, one-to-many and many-to-many
    # relationships between models. Each model uses an association to describe its role in
    # the relation. The +belongs_to+ association is always used in the model that has
    # the foreign key.
    #
    # === One-to-one
    #
    # Use +has_one+ in the base, and +belongs_to+ in the associated model.
    #
    # class Employee < ActiveRecord::Base
    # has_one :office
    # end
    # class Office < ActiveRecord::Base
    # belongs_to :employee # foreign key - employee_id
    # end
    #
    # === One-to-many
    #
    # Use +has_many+ in the base, and +belongs_to+ in the associated model.
    #
    # class Manager < ActiveRecord::Base
    # has_many :employees
    # end
    # class Employee < ActiveRecord::Base
    # belongs_to :manager # foreign key - manager_id
    # end
    #
    # === Many-to-many
    #
    # There are two ways to build a many-to-many relationship.
    #
    # The first way uses a +has_many+ association with the <tt>:through</tt> option and a join model, so
    # there are two stages of associations.
    #
    # class Assignment < ActiveRecord::Base
    # belongs_to :programmer # foreign key - programmer_id
    # belongs_to :project # foreign key - project_id
    # end
    # class Programmer < ActiveRecord::Base
    # has_many :assignments
    # has_many :projects, :through => :assignments
    # end
    # class Project < ActiveRecord::Base
    # has_many :assignments
    # has_many :programmers, :through => :assignments
    # end
    #
    # For the second way, use +has_and_belongs_to_many+ in both models. This requires a join table
    # that has no corresponding model or primary key.
    #
    # class Programmer < ActiveRecord::Base
    # has_and_belongs_to_many :projects # foreign keys in the join table
    # end
    # class Project < ActiveRecord::Base
    # has_and_belongs_to_many :programmers # foreign keys in the join table
    # end
    #
    # Choosing which way to build a many-to-many relationship is not always simple.
    # If you need to work with the relationship model as its own entity,
    # use <tt>has_many :through</tt>. Use +has_and_belongs_to_many+ when working with legacy schemas or when
    # you never work directly with the relationship itself.
    #
    # == Is it a +belongs_to+ or +has_one+ association?
    #
    # Both express a 1-1 relationship. The difference is mostly where to place the foreign
    # key, which goes on the table for the class declaring the +belongs_to+ relationship.
    #
    # class User < ActiveRecord::Base
    # # I reference an account.
    # belongs_to :account
    # end
    #
    # class Account < ActiveRecord::Base
    # # One user references me.
    # has_one :user
    # end
    #
    # The tables for these classes could look something like:
    #
    # CREATE TABLE users (
    # id int(11) NOT NULL auto_increment,
    # account_id int(11) default NULL,
    # name varchar default NULL,
    # PRIMARY KEY (id)
    # )
    #
    # CREATE TABLE accounts (
    # id int(11) NOT NULL auto_increment,
    # name varchar default NULL,
    # PRIMARY KEY (id)
    # )
    #
    # == Unsaved objects and associations
    #
    # You can manipulate objects and associations before they are saved to the database, but
    # there is some special behavior you should be aware of, mostly involving the saving of
    # associated objects.
    #
    # You can set the :autosave option on a <tt>has_one</tt>, <tt>belongs_to</tt>,
    # <tt>has_many</tt>, or <tt>has_and_belongs_to_many</tt> association. Setting it
    # to +true+ will _always_ save the members, whereas setting it to +false+ will
    # _never_ save the members. More details about :autosave option is available at
    # autosave_association.rb .
    #
    # === One-to-one associations
    #
    # * Assigning an object to a +has_one+ association automatically saves that object and
    # the object being replaced (if there is one), in order to update their foreign
    # keys - except if the parent object is unsaved (<tt>new_record? == true</tt>).
    # * If either of these saves fail (due to one of the objects being invalid), an
    # <tt>ActiveRecord::RecordNotSaved</tt> exception is raised and the assignment is
    # cancelled.
    # * If you wish to assign an object to a +has_one+ association without saving it,
    # use the <tt>build_association</tt> method (documented below). The object being
    # replaced will still be saved to update its foreign key.
    # * Assigning an object to a +belongs_to+ association does not save the object, since
    # the foreign key field belongs on the parent. It does not save the parent either.
    #
    # === Collections
    #
    # * Adding an object to a collection (+has_many+ or +has_and_belongs_to_many+) automatically
    # saves that object, except if the parent object (the owner of the collection) is not yet
    # stored in the database.
    # * If saving any of the objects being added to a collection (via <tt>push</tt> or similar)
    # fails, then <tt>push</tt> returns +false+.
    # * If saving fails while replacing the collection (via <tt>association=</tt>), an
    # <tt>ActiveRecord::RecordNotSaved</tt> exception is raised and the assignment is
    # cancelled.
    # * You can add an object to a collection without automatically saving it by using the
    # <tt>collection.build</tt> method (documented below).
    # * All unsaved (<tt>new_record? == true</tt>) members of the collection are automatically
    # saved when the parent is saved.
    #
    # === Association callbacks
    #
    # Similar to the normal callbacks that hook into the life cycle of an Active Record object,
    # you can also define callbacks that get triggered when you add an object to or remove an
    # object from an association collection.
    #
    # class Project
    # has_and_belongs_to_many :developers, :after_add => :evaluate_velocity
    #
    # def evaluate_velocity(developer)
    # ...
    # end
    # end
    #
    # It's possible to stack callbacks by passing them as an array. Example:
    #
    # class Project
    # has_and_belongs_to_many :developers,
    # :after_add => [:evaluate_velocity, Proc.new { |p, d| p.shipping_date = Time.now}]
    # end
    #
    # Possible callbacks are: +before_add+, +after_add+, +before_remove+ and +after_remove+.
    #
    # Should any of the +before_add+ callbacks throw an exception, the object does not get
    # added to the collection. Same with the +before_remove+ callbacks; if an exception is
    # thrown the object doesn't get removed.
    #
    # === Association extensions
    #
    # The proxy objects that control the access to associations can be extended through anonymous
    # modules. This is especially beneficial for adding new finders, creators, and other
    # factory-type methods that are only used as part of this association.
    #
    # class Account < ActiveRecord::Base
    # has_many :people do
    # def find_or_create_by_name(name)
    # first_name, last_name = name.split(" ", 2)
    # find_or_create_by_first_name_and_last_name(first_name, last_name)
    # end
    # end
    # end
    #
    # person = Account.first.people.find_or_create_by_name("David Heinemeier Hansson")
    # person.first_name # => "David"
    # person.last_name # => "Heinemeier Hansson"
    #
    # If you need to share the same extensions between many associations, you can use a named
    # extension module.
    #
    # module FindOrCreateByNameExtension
    # def find_or_create_by_name(name)
    # first_name, last_name = name.split(" ", 2)
    # find_or_create_by_first_name_and_last_name(first_name, last_name)
    # end
    # end
    #
    # class Account < ActiveRecord::Base
    # has_many :people, :extend => FindOrCreateByNameExtension
    # end
    #
    # class Company < ActiveRecord::Base
    # has_many :people, :extend => FindOrCreateByNameExtension
    # end
    #
    # If you need to use multiple named extension modules, you can specify an array of modules
    # with the <tt>:extend</tt> option.
    # In the case of name conflicts between methods in the modules, methods in modules later
    # in the array supercede those earlier in the array.
    #
    # class Account < ActiveRecord::Base
    # has_many :people, :extend => [FindOrCreateByNameExtension, FindRecentExtension]
    # end
    #
    # Some extensions can only be made to work with knowledge of the association's internals.
    # Extensions can access relevant state using the following methods (where +items+ is the
    # name of the association):
    #
    # * <tt>record.association(:items).owner</tt> - Returns the object the association is part of.
    # * <tt>record.association(:items).reflection</tt> - Returns the reflection object that describes the association.
    # * <tt>record.association(:items).target</tt> - Returns the associated object for +belongs_to+ and +has_one+, or
    # the collection of associated objects for +has_many+ and +has_and_belongs_to_many+.
    #
    # However, inside the actual extension code, you will not have access to the <tt>record</tt> as
    # above. In this case, you can access <tt>proxy_association</tt>. For example,
    # <tt>record.association(:items)</tt> and <tt>record.items.proxy_association</tt> will return
    # the same object, allowing you to make calls like <tt>proxy_association.owner</tt> inside
    # association extensions.
    #
    # === Association Join Models
    #
    # Has Many associations can be configured with the <tt>:through</tt> option to use an
    # explicit join model to retrieve the data. This operates similarly to a
    # +has_and_belongs_to_many+ association. The advantage is that you're able to add validations,
    # callbacks, and extra attributes on the join model. Consider the following schema:
    #
    # class Author < ActiveRecord::Base
    # has_many :authorships
    # has_many :books, :through => :authorships
    # end
    #
    # class Authorship < ActiveRecord::Base
    # belongs_to :author
    # belongs_to :book
    # end
    #
    # @author = Author.first
    # @author.authorships.collect { |a| a.book } # selects all books that the author's authorships belong to
    # @author.books # selects all books by using the Authorship join model
    #
    # You can also go through a +has_many+ association on the join model:
    #
    # class Firm < ActiveRecord::Base
    # has_many :clients
    # has_many :invoices, :through => :clients
    # end
    #
    # class Client < ActiveRecord::Base
    # belongs_to :firm
    # has_many :invoices
    # end
    #
    # class Invoice < ActiveRecord::Base
    # belongs_to :client
    # end
    #
    # @firm = Firm.first
    # @firm.clients.collect { |c| c.invoices }.flatten # select all invoices for all clients of the firm
    # @firm.invoices # selects all invoices by going through the Client join model
    #
    # Similarly you can go through a +has_one+ association on the join model:
    #
    # class Group < ActiveRecord::Base
    # has_many :users
    # has_many :avatars, :through => :users
    # end
    #
    # class User < ActiveRecord::Base
    # belongs_to :group
    # has_one :avatar
    # end
    #
    # class Avatar < ActiveRecord::Base
    # belongs_to :user
    # end
    #
    # @group = Group.first
    # @group.users.collect { |u| u.avatar }.flatten # select all avatars for all users in the group
    # @group.avatars # selects all avatars by going through the User join model.
    #
    # An important caveat with going through +has_one+ or +has_many+ associations on the
    # join model is that these associations are *read-only*. For example, the following
    # would not work following the previous example:
    #
    # @group.avatars << Avatar.new # this would work if User belonged_to Avatar rather than the other way around
    # @group.avatars.delete(@group.avatars.last) # so would this
    #
    # If you are using a +belongs_to+ on the join model, it is a good idea to set the
    # <tt>:inverse_of</tt> option on the +belongs_to+, which will mean that the following example
    # works correctly (where <tt>tags</tt> is a +has_many+ <tt>:through</tt> association):
    #
    # @post = Post.first
    # @tag = @post.tags.build :name => "ruby"
    # @tag.save
    #
    # The last line ought to save the through record (a <tt>Taggable</tt>). This will only work if the
    # <tt>:inverse_of</tt> is set:
    #
    # class Taggable < ActiveRecord::Base
    # belongs_to :post
    # belongs_to :tag, :inverse_of => :taggings
    # end
    #
    # === Nested Associations
    #
    # You can actually specify *any* association with the <tt>:through</tt> option, including an
    # association which has a <tt>:through</tt> option itself. For example:
    #
    # class Author < ActiveRecord::Base
    # has_many :posts
    # has_many :comments, :through => :posts
    # has_many :commenters, :through => :comments
    # end
    #
    # class Post < ActiveRecord::Base
    # has_many :comments
    # end
    #
    # class Comment < ActiveRecord::Base
    # belongs_to :commenter
    # end
    #
    # @author = Author.first
    # @author.commenters # => People who commented on posts written by the author
    #
    # An equivalent way of setting up this association this would be:
    #
    # class Author < ActiveRecord::Base
    # has_many :posts
    # has_many :commenters, :through => :posts
    # end
    #
    # class Post < ActiveRecord::Base
    # has_many :comments
    # has_many :commenters, :through => :comments
    # end
    #
    # class Comment < ActiveRecord::Base
    # belongs_to :commenter
    # end
    #
    # When using nested association, you will not be able to modify the association because there
    # is not enough information to know what modification to make. For example, if you tried to
    # add a <tt>Commenter</tt> in the example above, there would be no way to tell how to set up the
    # intermediate <tt>Post</tt> and <tt>Comment</tt> objects.
    #
    # === Polymorphic Associations
    #
    # Polymorphic associations on models are not restricted on what types of models they
    # can be associated with. Rather, they specify an interface that a +has_many+ association
    # must adhere to.
    #
    # class Asset < ActiveRecord::Base
    # belongs_to :attachable, :polymorphic => true
    # end
    #
    # class Post < ActiveRecord::Base
    # has_many :assets, :as => :attachable # The :as option specifies the polymorphic interface to use.
    # end
    #
    # @asset.attachable = @post
    #
    # This works by using a type column in addition to a foreign key to specify the associated
    # record. In the Asset example, you'd need an +attachable_id+ integer column and an
    # +attachable_type+ string column.
    #
    # Using polymorphic associations in combination with single table inheritance (STI) is
    # a little tricky. In order for the associations to work as expected, ensure that you
    # store the base model for the STI models in the type column of the polymorphic
    # association. To continue with the asset example above, suppose there are guest posts
    # and member posts that use the posts table for STI. In this case, there must be a +type+
    # column in the posts table.
    #
    # class Asset < ActiveRecord::Base
    # belongs_to :attachable, :polymorphic => true
    #
    # def attachable_type=(sType)
    # super(sType.to_s.classify.constantize.base_class.to_s)
    # end
    # end
    #
    # class Post < ActiveRecord::Base
    # # because we store "Post" in attachable_type now :dependent => :destroy will work
    # has_many :assets, :as => :attachable, :dependent => :destroy
    # end
    #
    # class GuestPost < Post
    # end
    #
    # class MemberPost < Post
    # end
    #
    # == Caching
    #
    # All of the methods are built on a simple caching principle that will keep the result
    # of the last query around unless specifically instructed not to. The cache is even
    # shared across methods to make it even cheaper to use the macro-added methods without
    # worrying too much about performance at the first go.
    #
    # project.milestones # fetches milestones from the database
    # project.milestones.size # uses the milestone cache
    # project.milestones.empty? # uses the milestone cache
    # project.milestones(true).size # fetches milestones from the database
    # project.milestones # uses the milestone cache
    #
    # == Eager loading of associations
    #
    # Eager loading is a way to find objects of a certain class and a number of named associations.
    # This is one of the easiest ways of to prevent the dreaded 1+N problem in which fetching 100
    # posts that each need to display their author triggers 101 database queries. Through the
    # use of eager loading, the 101 queries can be reduced to 2.
    #
    # class Post < ActiveRecord::Base
    # belongs_to :author
    # has_many :comments
    # end
    #
    # Consider the following loop using the class above:
    #
    # Post.all.each do |post|
    # puts "Post: " + post.title
    # puts "Written by: " + post.author.name
    # puts "Last comment on: " + post.comments.first.created_on
    # end
    #
    # To iterate over these one hundred posts, we'll generate 201 database queries. Let's
    # first just optimize it for retrieving the author:
    #
    # Post.includes(:author).each do |post|
    #
    # This references the name of the +belongs_to+ association that also used the <tt>:author</tt>
    # symbol. After loading the posts, find will collect the +author_id+ from each one and load
    # all the referenced authors with one query. Doing so will cut down the number of queries
    # from 201 to 102.
    #
    # We can improve upon the situation further by referencing both associations in the finder with:
    #
    # Post.includes(:author, :comments).each do |post|
    #
    # This will load all comments with a single query. This reduces the total number of queries
    # to 3. More generally the number of queries will be 1 plus the number of associations
    # named (except if some of the associations are polymorphic +belongs_to+ - see below).
    #
    # To include a deep hierarchy of associations, use a hash:
    #
    # Post.includes(:author, {:comments => {:author => :gravatar}}).each do |post|
    #
    # That'll grab not only all the comments but all their authors and gravatar pictures.
    # You can mix and match symbols, arrays and hashes in any combination to describe the
    # associations you want to load.
    #
    # All of this power shouldn't fool you into thinking that you can pull out huge amounts
    # of data with no performance penalty just because you've reduced the number of queries.
    # The database still needs to send all the data to Active Record and it still needs to
    # be processed. So it's no catch-all for performance problems, but it's a great way to
    # cut down on the number of queries in a situation as the one described above.
    #
    # Since only one table is loaded at a time, conditions or orders cannot reference tables
    # other than the main one. If this is the case Active Record falls back to the previously
    # used LEFT OUTER JOIN based strategy. For example
    #
    # Post.includes([:author, :comments]).where(['comments.approved = ?', true]).all
    #
    # This will result in a single SQL query with joins along the lines of:
    # <tt>LEFT OUTER JOIN comments ON comments.post_id = posts.id</tt> and
    # <tt>LEFT OUTER JOIN authors ON authors.id = posts.author_id</tt>. Note that using conditions
    # like this can have unintended consequences.
    # In the above example posts with no approved comments are not returned at all, because
    # the conditions apply to the SQL statement as a whole and not just to the association.
    # You must disambiguate column references for this fallback to happen, for example
    # <tt>:order => "author.name DESC"</tt> will work but <tt>:order => "name DESC"</tt> will not.
    #
    # If you do want eager load only some members of an association it is usually more natural
    # to include an association which has conditions defined on it:
    #
    # class Post < ActiveRecord::Base
    # has_many :approved_comments, :class_name => 'Comment', :conditions => ['approved = ?', true]
    # end
    #
    # Post.includes(:approved_comments)
    #
    # This will load posts and eager load the +approved_comments+ association, which contains
    # only those comments that have been approved.
    #
    # If you eager load an association with a specified <tt>:limit</tt> option, it will be ignored,
    # returning all the associated objects:
    #
    # class Picture < ActiveRecord::Base
    # has_many :most_recent_comments, :class_name => 'Comment', :order => 'id DESC', :limit => 10
    # end
    #
    # Picture.includes(:most_recent_comments).first.most_recent_comments # => returns all associated comments.
    #
    # When eager loaded, conditions are interpolated in the context of the model class, not
    # the model instance. Conditions are lazily interpolated before the actual model exists.
    #
    # Eager loading is supported with polymorphic associations.
    #
    # class Address < ActiveRecord::Base
    # belongs_to :addressable, :polymorphic => true
    # end
    #
    # A call that tries to eager load the addressable model
    #
    # Address.includes(:addressable)
    #
    # This will execute one query to load the addresses and load the addressables with one
    # query per addressable type.
    # For example if all the addressables are either of class Person or Company then a total
    # of 3 queries will be executed. The list of addressable types to load is determined on
    # the back of the addresses loaded. This is not supported if Active Record has to fallback
    # to the previous implementation of eager loading and will raise ActiveRecord::EagerLoadPolymorphicError.
    # The reason is that the parent model's type is a column value so its corresponding table
    # name cannot be put in the +FROM+/+JOIN+ clauses of that query.
    #
    # == Table Aliasing
    #
    # Active Record uses table aliasing in the case that a table is referenced multiple times
    # in a join. If a table is referenced only once, the standard table name is used. The
    # second time, the table is aliased as <tt>#{reflection_name}_#{parent_table_name}</tt>.
    # Indexes are appended for any more successive uses of the table name.
    #
    # Post.joins(:comments)
    # # => SELECT ... FROM posts INNER JOIN comments ON ...
    # Post.joins(:special_comments) # STI
    # # => SELECT ... FROM posts INNER JOIN comments ON ... AND comments.type = 'SpecialComment'
    # Post.joins(:comments, :special_comments) # special_comments is the reflection name, posts is the parent table name
    # # => SELECT ... FROM posts INNER JOIN comments ON ... INNER JOIN comments special_comments_posts
    #
    # Acts as tree example:
    #
    # TreeMixin.joins(:children)
    # # => SELECT ... FROM mixins INNER JOIN mixins childrens_mixins ...
    # TreeMixin.joins(:children => :parent)
    # # => SELECT ... FROM mixins INNER JOIN mixins childrens_mixins ...
    # INNER JOIN parents_mixins ...
    # TreeMixin.joins(:children => {:parent => :children})
    # # => SELECT ... FROM mixins INNER JOIN mixins childrens_mixins ...
    # INNER JOIN parents_mixins ...
    # INNER JOIN mixins childrens_mixins_2
    #
    # Has and Belongs to Many join tables use the same idea, but add a <tt>_join</tt> suffix:
    #
    # Post.joins(:categories)
    # # => SELECT ... FROM posts INNER JOIN categories_posts ... INNER JOIN categories ...
    # Post.joins(:categories => :posts)
    # # => SELECT ... FROM posts INNER JOIN categories_posts ... INNER JOIN categories ...
    # INNER JOIN categories_posts posts_categories_join INNER JOIN posts posts_categories
    # Post.joins(:categories => {:posts => :categories})
    # # => SELECT ... FROM posts INNER JOIN categories_posts ... INNER JOIN categories ...
    # INNER JOIN categories_posts posts_categories_join INNER JOIN posts posts_categories
    # INNER JOIN categories_posts categories_posts_join INNER JOIN categories categories_posts_2
    #
    # If you wish to specify your own custom joins using <tt>joins</tt> method, those table
    # names will take precedence over the eager associations:
    #
    # Post.joins(:comments).joins("inner join comments ...")
    # # => SELECT ... FROM posts INNER JOIN comments_posts ON ... INNER JOIN comments ...
    # Post.joins(:comments, :special_comments).joins("inner join comments ...")
    # # => SELECT ... FROM posts INNER JOIN comments comments_posts ON ...
    # INNER JOIN comments special_comments_posts ...
    # INNER JOIN comments ...
    #
    # Table aliases are automatically truncated according to the maximum length of table identifiers
    # according to the specific database.
    #
    # == Modules
    #
    # By default, associations will look for objects within the current module scope. Consider:
    #
    # module MyApplication
    # module Business
    # class Firm < ActiveRecord::Base
    # has_many :clients
    # end
    #
    # class Client < ActiveRecord::Base; end
    # end
    # end
    #
    # When <tt>Firm#clients</tt> is called, it will in turn call
    # <tt>MyApplication::Business::Client.find_all_by_firm_id(firm.id)</tt>.
    # If you want to associate with a class in another module scope, this can be done by
    # specifying the complete class name.
    #
    # module MyApplication
    # module Business
    # class Firm < ActiveRecord::Base; end
    # end
    #
    # module Billing
    # class Account < ActiveRecord::Base
    # belongs_to :firm, :class_name => "MyApplication::Business::Firm"
    # end
    # end
    # end
    #
    # == Bi-directional associations
    #
    # When you specify an association there is usually an association on the associated model
    # that specifies the same relationship in reverse. For example, with the following models:
    #
    # class Dungeon < ActiveRecord::Base
    # has_many :traps
    # has_one :evil_wizard
    # end
    #
    # class Trap < ActiveRecord::Base
    # belongs_to :dungeon
    # end
    #
    # class EvilWizard < ActiveRecord::Base
    # belongs_to :dungeon
    # end
    #
    # The +traps+ association on +Dungeon+ and the +dungeon+ association on +Trap+ are
    # the inverse of each other and the inverse of the +dungeon+ association on +EvilWizard+
    # is the +evil_wizard+ association on +Dungeon+ (and vice-versa). By default,
    # Active Record doesn't know anything about these inverse relationships and so no object
    # loading optimization is possible. For example:
    #
    # d = Dungeon.first
    # t = d.traps.first
    # d.level == t.dungeon.level # => true
    # d.level = 10
    # d.level == t.dungeon.level # => false
    #
    # The +Dungeon+ instances +d+ and <tt>t.dungeon</tt> in the above example refer to
    # the same object data from the database, but are actually different in-memory copies
    # of that data. Specifying the <tt>:inverse_of</tt> option on associations lets you tell
    # Active Record about inverse relationships and it will optimise object loading. For
    # example, if we changed our model definitions to:
    #
    # class Dungeon < ActiveRecord::Base
    # has_many :traps, :inverse_of => :dungeon
    # has_one :evil_wizard, :inverse_of => :dungeon
    # end
    #
    # class Trap < ActiveRecord::Base
    # belongs_to :dungeon, :inverse_of => :traps
    # end
    #
    # class EvilWizard < ActiveRecord::Base
    # belongs_to :dungeon, :inverse_of => :evil_wizard
    # end
    #
    # Then, from our code snippet above, +d+ and <tt>t.dungeon</tt> are actually the same
    # in-memory instance and our final <tt>d.level == t.dungeon.level</tt> will return +true+.
    #
    # There are limitations to <tt>:inverse_of</tt> support:
    #
    # * does not work with <tt>:through</tt> associations.
    # * does not work with <tt>:polymorphic</tt> associations.
    # * for +belongs_to+ associations +has_many+ inverse associations are ignored.
    #
    # == Deleting from associations
    #
    # === Dependent associations
    #
    # +has_many+, +has_one+ and +belongs_to+ associations support the <tt>:dependent</tt> option.
    # This allows you to specify that associated records should be deleted when the owner is
    # deleted.
    #
    # For example:
    #
    # class Author
    # has_many :posts, :dependent => :destroy
    # end
    # Author.find(1).destroy # => Will destroy all of the author's posts, too
    #
    # The <tt>:dependent</tt> option can have different values which specify how the deletion
    # is done. For more information, see the documentation for this option on the different
    # specific association types.
    #
    # === Delete or destroy?
    #
    # +has_many+ and +has_and_belongs_to_many+ associations have the methods <tt>destroy</tt>,
    # <tt>delete</tt>, <tt>destroy_all</tt> and <tt>delete_all</tt>.
    #
    # For +has_and_belongs_to_many+, <tt>delete</tt> and <tt>destroy</tt> are the same: they
    # cause the records in the join table to be removed.
    #
    # For +has_many+, <tt>destroy</tt> will always call the <tt>destroy</tt> method of the
    # record(s) being removed so that callbacks are run. However <tt>delete</tt> will either
    # do the deletion according to the strategy specified by the <tt>:dependent</tt> option, or
    # if no <tt>:dependent</tt> option is given, then it will follow the default strategy.
    # The default strategy is <tt>:nullify</tt> (set the foreign keys to <tt>nil</tt>), except for
    # +has_many+ <tt>:through</tt>, where the default strategy is <tt>delete_all</tt> (delete
    # the join records, without running their callbacks).
    #
    # There is also a <tt>clear</tt> method which is the same as <tt>delete_all</tt>, except that
    # it returns the association rather than the records which have been deleted.
    #
    # === What gets deleted?
    #
    # There is a potential pitfall here: +has_and_belongs_to_many+ and +has_many+ <tt>:through</tt>
    # associations have records in join tables, as well as the associated records. So when we
    # call one of these deletion methods, what exactly should be deleted?
    #
    # The answer is that it is assumed that deletion on an association is about removing the
    # <i>link</i> between the owner and the associated object(s), rather than necessarily the
    # associated objects themselves. So with +has_and_belongs_to_many+ and +has_many+
    # <tt>:through</tt>, the join records will be deleted, but the associated records won't.
    #
    # This makes sense if you think about it: if you were to call <tt>post.tags.delete(Tag.find_by_name('food'))</tt>
    # you would want the 'food' tag to be unlinked from the post, rather than for the tag itself
    # to be removed from the database.
    #
    # However, there are examples where this strategy doesn't make sense. For example, suppose
    # a person has many projects, and each project has many tasks. If we deleted one of a person's
    # tasks, we would probably not want the project to be deleted. In this scenario, the delete method
    # won't actually work: it can only be used if the association on the join model is a
    # +belongs_to+. In other situations you are expected to perform operations directly on
    # either the associated records or the <tt>:through</tt> association.
    #
    # With a regular +has_many+ there is no distinction between the "associated records"
    # and the "link", so there is only one choice for what gets deleted.
    #
    # With +has_and_belongs_to_many+ and +has_many+ <tt>:through</tt>, if you want to delete the
    # associated records themselves, you can always do something along the lines of
    # <tt>person.tasks.each(&:destroy)</tt>.
    #
    # == Type safety with <tt>ActiveRecord::AssociationTypeMismatch</tt>
    #
    # If you attempt to assign an object to an association that doesn't match the inferred
    # or specified <tt>:class_name</tt>, you'll get an <tt>ActiveRecord::AssociationTypeMismatch</tt>.
    #
    # == Options
    #
    # All of the association macros can be specialized through options. This makes cases
    # more complex than the simple and guessable ones possible.
    module ClassMethods
      # Specifies a one-to-many association. The following methods for retrieval and query of
      # collections of associated objects will be added:
      #
      # [collection(force_reload = false)]
      # Returns an array of all the associated objects.
      # An empty array is returned if none are found.
      # [collection<<(object, ...)]
      # Adds one or more objects to the collection by setting their foreign keys to the collection's primary key.
      # Note that this operation instantly fires update sql without waiting for the save or update call on the
      # parent object.
      # [collection.delete(object, ...)]
      # Removes one or more objects from the collection by setting their foreign keys to +NULL+.
      # Objects will be in addition destroyed if they're associated with <tt>:dependent => :destroy</tt>,
      # and deleted if they're associated with <tt>:dependent => :delete_all</tt>.
      #
      # If the <tt>:through</tt> option is used, then the join records are deleted (rather than
      # nullified) by default, but you can specify <tt>:dependent => :destroy</tt> or
      # <tt>:dependent => :nullify</tt> to override this.
      # [collection=objects]
      # Replaces the collections content by deleting and adding objects as appropriate. If the <tt>:through</tt>
      # option is true callbacks in the join models are triggered except destroy callbacks, since deletion is
      # direct.
      # [collection_singular_ids]
      # Returns an array of the associated objects' ids
      # [collection_singular_ids=ids]
      # Replace the collection with the objects identified by the primary keys in +ids+. This
      # method loads the models and calls <tt>collection=</tt>. See above.
      # [collection.clear]
      # Removes every object from the collection. This destroys the associated objects if they
      # are associated with <tt>:dependent => :destroy</tt>, deletes them directly from the
      # database if <tt>:dependent => :delete_all</tt>, otherwise sets their foreign keys to +NULL+.
      # If the <tt>:through</tt> option is true no destroy callbacks are invoked on the join models.
      # Join models are directly deleted.
      # [collection.empty?]
      # Returns +true+ if there are no associated objects.
      # [collection.size]
      # Returns the number of associated objects.
      # [collection.find(...)]
      # Finds an associated object according to the same rules as ActiveRecord::Base.find.
      # [collection.exists?(...)]
      # Checks whether an associated object with the given conditions exists.
      # Uses the same rules as ActiveRecord::Base.exists?.
      # [collection.build(attributes = {}, ...)]
      # Returns one or more new objects of the collection type that have been instantiated
      # with +attributes+ and linked to this object through a foreign key, but have not yet
      # been saved.
      # [collection.create(attributes = {})]
      # Returns a new object of the collection type that has been instantiated
      # with +attributes+, linked to this object through a foreign key, and that has already
      # been saved (if it passed the validation). *Note*: This only works if the base model
      # already exists in the DB, not if it is a new (unsaved) record!
      #
      # (*Note*: +collection+ is replaced with the symbol passed as the first argument, so
      # <tt>has_many :clients</tt> would add among others <tt>clients.empty?</tt>.)
      #
      # === Example
      #
      # Example: A Firm class declares <tt>has_many :clients</tt>, which will add:
      # * <tt>Firm#clients</tt> (similar to <tt>Clients.all :conditions => ["firm_id = ?", id]</tt>)
      # * <tt>Firm#clients<<</tt>
      # * <tt>Firm#clients.delete</tt>
      # * <tt>Firm#clients=</tt>
      # * <tt>Firm#client_ids</tt>
      # * <tt>Firm#client_ids=</tt>
      # * <tt>Firm#clients.clear</tt>
      # * <tt>Firm#clients.empty?</tt> (similar to <tt>firm.clients.size == 0</tt>)
      # * <tt>Firm#clients.size</tt> (similar to <tt>Client.count "firm_id = #{id}"</tt>)
      # * <tt>Firm#clients.find</tt> (similar to <tt>Client.find(id, :conditions => "firm_id = #{id}")</tt>)
      # * <tt>Firm#clients.exists?(:name => 'ACME')</tt> (similar to <tt>Client.exists?(:name => 'ACME', :firm_id => firm.id)</tt>)
      # * <tt>Firm#clients.build</tt> (similar to <tt>Client.new("firm_id" => id)</tt>)
      # * <tt>Firm#clients.create</tt> (similar to <tt>c = Client.new("firm_id" => id); c.save; c</tt>)
      # The declaration can also include an options hash to specialize the behavior of the association.
      #
      # === Options
      # [:class_name]
      # Specify the class name of the association. Use it only if that name can't be inferred
      # from the association name. So <tt>has_many :products</tt> will by default be linked
      # to the Product class, but if the real class name is SpecialProduct, you'll have to
      # specify it with this option.
      # [:conditions]
      # Specify the conditions that the associated objects must meet in order to be included as a +WHERE+
      # SQL fragment, such as <tt>price > 5 AND name LIKE 'B%'</tt>. Record creations from
      # the association are scoped if a hash is used.
      # <tt>has_many :posts, :conditions => {:published => true}</tt> will create published
      # posts with <tt>@blog.posts.create</tt> or <tt>@blog.posts.build</tt>.
      # [:order]
      # Specify the order in which the associated objects are returned as an <tt>ORDER BY</tt> SQL fragment,
      # such as <tt>last_name, first_name DESC</tt>.
      # [:foreign_key]
      # Specify the foreign key used for the association. By default this is guessed to be the name
      # of this class in lower-case and "_id" suffixed. So a Person class that makes a +has_many+
      # association will use "person_id" as the default <tt>:foreign_key</tt>.
      # [:primary_key]
      # Specify the method that returns the primary key used for the association. By default this is +id+.
      # [:dependent]
      # If set to <tt>:destroy</tt> all the associated objects are destroyed
      # alongside this object by calling their +destroy+ method. If set to <tt>:delete_all</tt> all associated
      # objects are deleted *without* calling their +destroy+ method. If set to <tt>:nullify</tt> all associated
      # objects' foreign keys are set to +NULL+ *without* calling their +save+ callbacks. If set to
      # <tt>:restrict</tt> this object raises an <tt>ActiveRecord::DeleteRestrictionError</tt> exception and
      # cannot be deleted if it has any associated objects.
      #
      # If using with the <tt>:through</tt> option, the association on the join model must be
      # a +belongs_to+, and the records which get deleted are the join records, rather than
      # the associated records.
      #
      # [:finder_sql]
      # Specify a complete SQL statement to fetch the association. This is a good way to go for complex
      # associations that depend on multiple tables. May be supplied as a string or a proc where interpolation is
      # required. Note: When this option is used, +find_in_collection+
      # is _not_ added.
      # [:counter_sql]
      # Specify a complete SQL statement to fetch the size of the association. If <tt>:finder_sql</tt> is
      # specified but not <tt>:counter_sql</tt>, <tt>:counter_sql</tt> will be generated by
      # replacing <tt>SELECT ... FROM</tt> with <tt>SELECT COUNT(*) FROM</tt>.
      # [:extend]
      # Specify a named module for extending the proxy. See "Association extensions".
      # [:include]
      # Specify second-order associations that should be eager loaded when the collection is loaded.
      # [:group]
      # An attribute name by which the result should be grouped. Uses the <tt>GROUP BY</tt> SQL-clause.
      # [:having]
      # Combined with +:group+ this can be used to filter the records that a <tt>GROUP BY</tt>
      # returns. Uses the <tt>HAVING</tt> SQL-clause.
      # [:limit]
      # An integer determining the limit on the number of rows that should be returned.
      # [:offset]
      # An integer determining the offset from where the rows should be fetched. So at 5,
      # it would skip the first 4 rows.
      # [:select]
      # By default, this is <tt>*</tt> as in <tt>SELECT * FROM</tt>, but can be changed if
      # you, for example, want to do a join but not include the joined columns. Do not forget
      # to include the primary and foreign keys, otherwise it will raise an error.
      # [:as]
      # Specifies a polymorphic interface (See <tt>belongs_to</tt>).
      # [:through]
      # Specifies an association through which to perform the query. This can be any other type
      # of association, including other <tt>:through</tt> associations. Options for <tt>:class_name</tt>,
      # <tt>:primary_key</tt> and <tt>:foreign_key</tt> are ignored, as the association uses the
      # source reflection.
      #
      # If the association on the join model is a +belongs_to+, the collection can be modified
      # and the records on the <tt>:through</tt> model will be automatically created and removed
      # as appropriate. Otherwise, the collection is read-only, so you should manipulate the
      # <tt>:through</tt> association directly.
      #
      # If you are going to modify the association (rather than just read from it), then it is
      # a good idea to set the <tt>:inverse_of</tt> option on the source association on the
      # join model. This allows associated records to be built which will automatically create
      # the appropriate join model records when they are saved. (See the 'Association Join Models'
      # section above.)
      # [:source]
      # Specifies the source association name used by <tt>has_many :through</tt> queries.
      # Only use it if the name cannot be inferred from the association.
      # <tt>has_many :subscribers, :through => :subscriptions</tt> will look for either <tt>:subscribers</tt> or
      # <tt>:subscriber</tt> on Subscription, unless a <tt>:source</tt> is given.
      # [:source_type]
      # Specifies type of the source association used by <tt>has_many :through</tt> queries where the source
      # association is a polymorphic +belongs_to+.
      # [:uniq]
      # If true, duplicates will be omitted from the collection. Useful in conjunction with <tt>:through</tt>.
      # [:readonly]
      # If true, all the associated objects are readonly through the association.
      # [:validate]
      # If +false+, don't validate the associated objects when saving the parent object. true by default.
      # [:autosave]
      # If true, always save the associated objects or destroy them if marked for destruction,
      # when saving the parent object. If false, never save or destroy the associated objects.
      # By default, only save associated objects that are new records.
      # [:inverse_of]
      # Specifies the name of the <tt>belongs_to</tt> association on the associated object
      # that is the inverse of this <tt>has_many</tt> association. Does not work in combination
      # with <tt>:through</tt> or <tt>:as</tt> options.
      # See ActiveRecord::Associations::ClassMethods's overview on Bi-directional associations for more detail.
      #
      # Option examples:
      # has_many :comments, :order => "posted_on"
      # has_many :comments, :include => :author
      # has_many :people, :class_name => "Person", :conditions => "deleted = 0", :order => "name"
      # has_many :tracks, :order => "position", :dependent => :destroy
      # has_many :comments, :dependent => :nullify
      # has_many :tags, :as => :taggable
      # has_many :reports, :readonly => true
      # has_many :subscribers, :through => :subscriptions, :source => :user
      # has_many :subscribers, :class_name => "Person", :finder_sql => Proc.new {
      # %Q{
      # SELECT DISTINCT *
      # FROM people p, post_subscriptions ps
      # WHERE ps.post_id = #{id} AND ps.person_id = p.id
      # ORDER BY p.first_name
      # }
      # }
      def has_many(name, options = {}, &extension)
        Builder::HasMany.build(self, name, options, &extension)
      end

      # Specifies a one-to-one association with another class. This method should only be used
      # if the other class contains the foreign key. If the current class contains the foreign key,
      # then you should use +belongs_to+ instead. See also ActiveRecord::Associations::ClassMethods's overview
      # on when to use has_one and when to use belongs_to.
      #
      # The following methods for retrieval and query of a single associated object will be added:
      #
      # [association(force_reload = false)]
      # Returns the associated object. +nil+ is returned if none is found.
      # [association=(associate)]
      # Assigns the associate object, extracts the primary key, sets it as the foreign key,
      # and saves the associate object.
      # [build_association(attributes = {})]
      # Returns a new object of the associated type that has been instantiated
      # with +attributes+ and linked to this object through a foreign key, but has not
      # yet been saved.
      # [create_association(attributes = {})]
      # Returns a new object of the associated type that has been instantiated
      # with +attributes+, linked to this object through a foreign key, and that
      # has already been saved (if it passed the validation).
      # [create_association!(attributes = {})]
      # Does the same as <tt>create_association</tt>, but raises <tt>ActiveRecord::RecordInvalid</tt>
      # if the record is invalid.
      #
      # (+association+ is replaced with the symbol passed as the first argument, so
      # <tt>has_one :manager</tt> would add among others <tt>manager.nil?</tt>.)
      #
      # === Example
      #
      # An Account class declares <tt>has_one :beneficiary</tt>, which will add:
      # * <tt>Account#beneficiary</tt> (similar to <tt>Beneficiary.first(:conditions => "account_id = #{id}")</tt>)
      # * <tt>Account#beneficiary=(beneficiary)</tt> (similar to <tt>beneficiary.account_id = account.id; beneficiary.save</tt>)
      # * <tt>Account#build_beneficiary</tt> (similar to <tt>Beneficiary.new("account_id" => id)</tt>)
      # * <tt>Account#create_beneficiary</tt> (similar to <tt>b = Beneficiary.new("account_id" => id); b.save; b</tt>)
      # * <tt>Account#create_beneficiary!</tt> (similar to <tt>b = Beneficiary.new("account_id" => id); b.save!; b</tt>)
      #
      # === Options
      #
      # The declaration can also include an options hash to specialize the behavior of the association.
      #
      # Options are:
      # [:class_name]
      # Specify the class name of the association. Use it only if that name can't be inferred
      # from the association name. So <tt>has_one :manager</tt> will by default be linked to the Manager class, but
      # if the real class name is Person, you'll have to specify it with this option.
      # [:conditions]
      # Specify the conditions that the associated object must meet in order to be included as a +WHERE+
      # SQL fragment, such as <tt>rank = 5</tt>. Record creation from the association is scoped if a hash
      # is used. <tt>has_one :account, :conditions => {:enabled => true}</tt> will create
      # an enabled account with <tt>@company.create_account</tt> or <tt>@company.build_account</tt>.
      # [:order]
      # Specify the order in which the associated objects are returned as an <tt>ORDER BY</tt> SQL fragment,
      # such as <tt>last_name, first_name DESC</tt>.
      # [:dependent]
      # If set to <tt>:destroy</tt>, the associated object is destroyed when this object is. If set to
      # <tt>:delete</tt>, the associated object is deleted *without* calling its destroy method.
      # If set to <tt>:nullify</tt>, the associated object's foreign key is set to +NULL+.
      # Also, association is assigned. If set to <tt>:restrict</tt> this object raises an
      # <tt>ActiveRecord::DeleteRestrictionError</tt> exception and cannot be deleted if it has any associated object.
      # [:foreign_key]
      # Specify the foreign key used for the association. By default this is guessed to be the name
      # of this class in lower-case and "_id" suffixed. So a Person class that makes a +has_one+ association
      # will use "person_id" as the default <tt>:foreign_key</tt>.
      # [:primary_key]
      # Specify the method that returns the primary key used for the association. By default this is +id+.
      # [:include]
      # Specify second-order associations that should be eager loaded when this object is loaded.
      # [:as]
      # Specifies a polymorphic interface (See <tt>belongs_to</tt>).
      # [:select]
      # By default, this is <tt>*</tt> as in <tt>SELECT * FROM</tt>, but can be changed if, for example,
      # you want to do a join but not include the joined columns. Do not forget to include the
      # primary and foreign keys, otherwise it will raise an error.
      # [:through]
      # Specifies a Join Model through which to perform the query. Options for <tt>:class_name</tt>,
      # <tt>:primary_key</tt>, and <tt>:foreign_key</tt> are ignored, as the association uses the
      # source reflection. You can only use a <tt>:through</tt> query through a <tt>has_one</tt>
      # or <tt>belongs_to</tt> association on the join model.
      # [:source]
      # Specifies the source association name used by <tt>has_one :through</tt> queries.
      # Only use it if the name cannot be inferred from the association.
      # <tt>has_one :favorite, :through => :favorites</tt> will look for a
      # <tt>:favorite</tt> on Favorite, unless a <tt>:source</tt> is given.
      # [:source_type]
      # Specifies type of the source association used by <tt>has_one :through</tt> queries where the source
      # association is a polymorphic +belongs_to+.
      # [:readonly]
      # If true, the associated object is readonly through the association.
      # [:validate]
      # If +false+, don't validate the associated object when saving the parent object. +false+ by default.
      # [:autosave]
      # If true, always save the associated object or destroy it if marked for destruction,
      # when saving the parent object. If false, never save or destroy the associated object.
      # By default, only save the associated object if it's a new record.
      # [:inverse_of]
      # Specifies the name of the <tt>belongs_to</tt> association on the associated object
      # that is the inverse of this <tt>has_one</tt> association. Does not work in combination
      # with <tt>:through</tt> or <tt>:as</tt> options.
      # See ActiveRecord::Associations::ClassMethods's overview on Bi-directional associations for more detail.
      #
      # Option examples:
      # has_one :credit_card, :dependent => :destroy # destroys the associated credit card
      # has_one :credit_card, :dependent => :nullify # updates the associated records foreign
      # # key value to NULL rather than destroying it
      # has_one :last_comment, :class_name => "Comment", :order => "posted_on"
      # has_one :project_manager, :class_name => "Person", :conditions => "role = 'project_manager'"
      # has_one :attachment, :as => :attachable
      # has_one :boss, :readonly => :true
      # has_one :club, :through => :membership
      # has_one :primary_address, :through => :addressables, :conditions => ["addressable.primary = ?", true], :source => :addressable
      def has_one(name, options = {})
        Builder::HasOne.build(self, name, options)
      end

      # Specifies a one-to-one association with another class. This method should only be used
      # if this class contains the foreign key. If the other class contains the foreign key,
      # then you should use +has_one+ instead. See also ActiveRecord::Associations::ClassMethods's overview
      # on when to use +has_one+ and when to use +belongs_to+.
      #
      # Methods will be added for retrieval and query for a single associated object, for which
      # this object holds an id:
      #
      # [association(force_reload = false)]
      # Returns the associated object. +nil+ is returned if none is found.
      # [association=(associate)]
      # Assigns the associate object, extracts the primary key, and sets it as the foreign key.
      # [build_association(attributes = {})]
      # Returns a new object of the associated type that has been instantiated
      # with +attributes+ and linked to this object through a foreign key, but has not yet been saved.
      # [create_association(attributes = {})]
      # Returns a new object of the associated type that has been instantiated
      # with +attributes+, linked to this object through a foreign key, and that
      # has already been saved (if it passed the validation).
      # [create_association!(attributes = {})]
      # Does the same as <tt>create_association</tt>, but raises <tt>ActiveRecord::RecordInvalid</tt>
      # if the record is invalid.
      #
      # (+association+ is replaced with the symbol passed as the first argument, so
      # <tt>belongs_to :author</tt> would add among others <tt>author.nil?</tt>.)
      #
      # === Example
      #
      # A Post class declares <tt>belongs_to :author</tt>, which will add:
      # * <tt>Post#author</tt> (similar to <tt>Author.find(author_id)</tt>)
      # * <tt>Post#author=(author)</tt> (similar to <tt>post.author_id = author.id</tt>)
      # * <tt>Post#build_author</tt> (similar to <tt>post.author = Author.new</tt>)
      # * <tt>Post#create_author</tt> (similar to <tt>post.author = Author.new; post.author.save; post.author</tt>)
      # * <tt>Post#create_author!</tt> (similar to <tt>post.author = Author.new; post.author.save!; post.author</tt>)
      # The declaration can also include an options hash to specialize the behavior of the association.
      #
      # === Options
      #
      # [:class_name]
      # Specify the class name of the association. Use it only if that name can't be inferred
      # from the association name. So <tt>belongs_to :author</tt> will by default be linked to the Author class, but
      # if the real class name is Person, you'll have to specify it with this option.
      # [:conditions]
      # Specify the conditions that the associated object must meet in order to be included as a +WHERE+
      # SQL fragment, such as <tt>authorized = 1</tt>.
      # [:select]
      # By default, this is <tt>*</tt> as in <tt>SELECT * FROM</tt>, but can be changed
      # if, for example, you want to do a join but not include the joined columns. Do not
      # forget to include the primary and foreign keys, otherwise it will raise an error.
      # [:foreign_key]
      # Specify the foreign key used for the association. By default this is guessed to be the name
      # of the association with an "_id" suffix. So a class that defines a <tt>belongs_to :person</tt>
      # association will use "person_id" as the default <tt>:foreign_key</tt>. Similarly,
      # <tt>belongs_to :favorite_person, :class_name => "Person"</tt> will use a foreign key
      # of "favorite_person_id".
      # [:foreign_type]
      # Specify the column used to store the associated object's type, if this is a polymorphic
      # association. By default this is guessed to be the name of the association with a "_type"
      # suffix. So a class that defines a <tt>belongs_to :taggable, :polymorphic => true</tt>
      # association will use "taggable_type" as the default <tt>:foreign_type</tt>.
      # [:primary_key]
      # Specify the method that returns the primary key of associated object used for the association.
      # By default this is id.
      # [:dependent]
      # If set to <tt>:destroy</tt>, the associated object is destroyed when this object is. If set to
      # <tt>:delete</tt>, the associated object is deleted *without* calling its destroy method.
      # This option should not be specified when <tt>belongs_to</tt> is used in conjunction with
      # a <tt>has_many</tt> relationship on another class because of the potential to leave
      # orphaned records behind.
      # [:counter_cache]
      # Caches the number of belonging objects on the associate class through the use of +increment_counter+
      # and +decrement_counter+. The counter cache is incremented when an object of this
      # class is created and decremented when it's destroyed. This requires that a column
      # named <tt>#{table_name}_count</tt> (such as +comments_count+ for a belonging Comment class)
      # is used on the associate class (such as a Post class). You can also specify a custom counter
      # cache column by providing a column name instead of a +true+/+false+ value to this
      # option (e.g., <tt>:counter_cache => :my_custom_counter</tt>.)
      # Note: Specifying a counter cache will add it to that model's list of readonly attributes
      # using +attr_readonly+.
      # [:include]
      # Specify second-order associations that should be eager loaded when this object is loaded.
      # [:polymorphic]
      # Specify this association is a polymorphic association by passing +true+.
      # Note: If you've enabled the counter cache, then you may want to add the counter cache attribute
      # to the +attr_readonly+ list in the associated classes (e.g. <tt>class Post; attr_readonly :comments_count; end</tt>).
      # [:readonly]
      # If true, the associated object is readonly through the association.
      # [:validate]
      # If +false+, don't validate the associated objects when saving the parent object. +false+ by default.
      # [:autosave]
      # If true, always save the associated object or destroy it if marked for destruction, when
      # saving the parent object.
      # If false, never save or destroy the associated object.
      # By default, only save the associated object if it's a new record.
      # [:touch]
      # If true, the associated object will be touched (the updated_at/on attributes set to now)
      # when this record is either saved or destroyed. If you specify a symbol, that attribute
      # will be updated with the current time in addition to the updated_at/on attribute.
      # [:inverse_of]
      # Specifies the name of the <tt>has_one</tt> or <tt>has_many</tt> association on the associated
      # object that is the inverse of this <tt>belongs_to</tt> association. Does not work in
      # combination with the <tt>:polymorphic</tt> options.
      # See ActiveRecord::Associations::ClassMethods's overview on Bi-directional associations for more detail.
      #
      # Option examples:
      # belongs_to :firm, :foreign_key => "client_of"
      # belongs_to :person, :primary_key => "name", :foreign_key => "person_name"
      # belongs_to :author, :class_name => "Person", :foreign_key => "author_id"
      # belongs_to :valid_coupon, :class_name => "Coupon", :foreign_key => "coupon_id",
      # :conditions => 'discounts > #{payments_count}'
      # belongs_to :attachable, :polymorphic => true
      # belongs_to :project, :readonly => true
      # belongs_to :post, :counter_cache => true
      # belongs_to :company, :touch => true
      # belongs_to :company, :touch => :employees_last_updated_at
      def belongs_to(name, options = {})
        Builder::BelongsTo.build(self, name, options)
      end

      # Specifies a many-to-many relationship with another class. This associates two classes via an
      # intermediate join table. Unless the join table is explicitly specified as an option, it is
      # guessed using the lexical order of the class names. So a join between Developer and Project
      # will give the default join table name of "developers_projects" because "D" outranks "P".
      # Note that this precedence is calculated using the <tt><</tt> operator for String. This
      # means that if the strings are of different lengths, and the strings are equal when compared
      # up to the shortest length, then the longer string is considered of higher
      # lexical precedence than the shorter one. For example, one would expect the tables "paper_boxes" and "papers"
      # to generate a join table name of "papers_paper_boxes" because of the length of the name "paper_boxes",
      # but it in fact generates a join table name of "paper_boxes_papers". Be aware of this caveat, and use the
      # custom <tt>:join_table</tt> option if you need to.
      #
      # The join table should not have a primary key or a model associated with it. You must manually generate the
      # join table with a migration such as this:
      #
      # class CreateDevelopersProjectsJoinTable < ActiveRecord::Migration
      # def change
      # create_table :developers_projects, :id => false do |t|
      # t.integer :developer_id
      # t.integer :project_id
      # end
      # end
      # end
      #
      # It's also a good idea to add indexes to each of those columns to speed up the joins process.
      # However, in MySQL it is advised to add a compound index for both of the columns as MySQL only
      # uses one index per table during the lookup.
      #
      # Adds the following methods for retrieval and query:
      #
      # [collection(force_reload = false)]
      # Returns an array of all the associated objects.
      # An empty array is returned if none are found.
      # [collection<<(object, ...)]
      # Adds one or more objects to the collection by creating associations in the join table
      # (<tt>collection.push</tt> and <tt>collection.concat</tt> are aliases to this method).
      # Note that this operation instantly fires update sql without waiting for the save or update call on the
      # parent object.
      # [collection.delete(object, ...)]
      # Removes one or more objects from the collection by removing their associations from the join table.
      # This does not destroy the objects.
      # [collection=objects]
      # Replaces the collection's content by deleting and adding objects as appropriate.
      # [collection_singular_ids]
      # Returns an array of the associated objects' ids.
      # [collection_singular_ids=ids]
      # Replace the collection by the objects identified by the primary keys in +ids+.
      # [collection.clear]
      # Removes every object from the collection. This does not destroy the objects.
      # [collection.empty?]
      # Returns +true+ if there are no associated objects.
      # [collection.size]
      # Returns the number of associated objects.
      # [collection.find(id)]
      # Finds an associated object responding to the +id+ and that
      # meets the condition that it has to be associated with this object.
      # Uses the same rules as ActiveRecord::Base.find.
      # [collection.exists?(...)]
      # Checks whether an associated object with the given conditions exists.
      # Uses the same rules as ActiveRecord::Base.exists?.
      # [collection.build(attributes = {})]
      # Returns a new object of the collection type that has been instantiated
      # with +attributes+ and linked to this object through the join table, but has not yet been saved.
      # [collection.create(attributes = {})]
      # Returns a new object of the collection type that has been instantiated
      # with +attributes+, linked to this object through the join table, and that has already been
      # saved (if it passed the validation).
      #
      # (+collection+ is replaced with the symbol passed as the first argument, so
      # <tt>has_and_belongs_to_many :categories</tt> would add among others <tt>categories.empty?</tt>.)
      #
      # === Example
      #
      # A Developer class declares <tt>has_and_belongs_to_many :projects</tt>, which will add:
      # * <tt>Developer#projects</tt>
      # * <tt>Developer#projects<<</tt>
      # * <tt>Developer#projects.delete</tt>
      # * <tt>Developer#projects=</tt>
      # * <tt>Developer#project_ids</tt>
      # * <tt>Developer#project_ids=</tt>
      # * <tt>Developer#projects.clear</tt>
      # * <tt>Developer#projects.empty?</tt>
      # * <tt>Developer#projects.size</tt>
      # * <tt>Developer#projects.find(id)</tt>
      # * <tt>Developer#projects.exists?(...)</tt>
      # * <tt>Developer#projects.build</tt> (similar to <tt>Project.new("developer_id" => id)</tt>)
      # * <tt>Developer#projects.create</tt> (similar to <tt>c = Project.new("developer_id" => id); c.save; c</tt>)
      # The declaration may include an options hash to specialize the behavior of the association.
      #
      # === Options
      #
      # [:class_name]
      # Specify the class name of the association. Use it only if that name can't be inferred
      # from the association name. So <tt>has_and_belongs_to_many :projects</tt> will by default be linked to the
      # Project class, but if the real class name is SuperProject, you'll have to specify it with this option.
      # [:join_table]
      # Specify the name of the join table if the default based on lexical order isn't what you want.
      # <b>WARNING:</b> If you're overwriting the table name of either class, the +table_name+ method
      # MUST be declared underneath any +has_and_belongs_to_many+ declaration in order to work.
      # [:foreign_key]
      # Specify the foreign key used for the association. By default this is guessed to be the name
      # of this class in lower-case and "_id" suffixed. So a Person class that makes
      # a +has_and_belongs_to_many+ association to Project will use "person_id" as the
      # default <tt>:foreign_key</tt>.
      # [:association_foreign_key]
      # Specify the foreign key used for the association on the receiving side of the association.
      # By default this is guessed to be the name of the associated class in lower-case and "_id" suffixed.
      # So if a Person class makes a +has_and_belongs_to_many+ association to Project,
      # the association will use "project_id" as the default <tt>:association_foreign_key</tt>.
      # [:conditions]
      # Specify the conditions that the associated object must meet in order to be included as a +WHERE+
      # SQL fragment, such as <tt>authorized = 1</tt>. Record creations from the association are
      # scoped if a hash is used.
      # <tt>has_many :posts, :conditions => {:published => true}</tt> will create published posts with <tt>@blog.posts.create</tt>
      # or <tt>@blog.posts.build</tt>.
      # [:order]
      # Specify the order in which the associated objects are returned as an <tt>ORDER BY</tt> SQL fragment,
      # such as <tt>last_name, first_name DESC</tt>
      # [:uniq]
      # If true, duplicate associated objects will be ignored by accessors and query methods.
      # [:finder_sql]
      # Overwrite the default generated SQL statement used to fetch the association with a manual statement
      # [:counter_sql]
      # Specify a complete SQL statement to fetch the size of the association. If <tt>:finder_sql</tt> is
      # specified but not <tt>:counter_sql</tt>, <tt>:counter_sql</tt> will be generated by
      # replacing <tt>SELECT ... FROM</tt> with <tt>SELECT COUNT(*) FROM</tt>.
      # [:delete_sql]
      # Overwrite the default generated SQL statement used to remove links between the associated
      # classes with a manual statement.
      # [:insert_sql]
      # Overwrite the default generated SQL statement used to add links between the associated classes
      # with a manual statement.
      # [:extend]
      # Anonymous module for extending the proxy, see "Association extensions".
      # [:include]
      # Specify second-order associations that should be eager loaded when the collection is loaded.
      # [:group]
      # An attribute name by which the result should be grouped. Uses the <tt>GROUP BY</tt> SQL-clause.
      # [:having]
      # Combined with +:group+ this can be used to filter the records that a <tt>GROUP BY</tt> returns.
      # Uses the <tt>HAVING</tt> SQL-clause.
      # [:limit]
      # An integer determining the limit on the number of rows that should be returned.
      # [:offset]
      # An integer determining the offset from where the rows should be fetched. So at 5,
      # it would skip the first 4 rows.
      # [:select]
      # By default, this is <tt>*</tt> as in <tt>SELECT * FROM</tt>, but can be changed if, for example,
      # you want to do a join but not include the joined columns. Do not forget to include the primary
      # and foreign keys, otherwise it will raise an error.
      # [:readonly]
      # If true, all the associated objects are readonly through the association.
      # [:validate]
      # If +false+, don't validate the associated objects when saving the parent object. +true+ by default.
      # [:autosave]
      # If true, always save the associated objects or destroy them if marked for destruction, when
      # saving the parent object.
      # If false, never save or destroy the associated objects.
      # By default, only save associated objects that are new records.
      #
      # Option examples:
      # has_and_belongs_to_many :projects
      # has_and_belongs_to_many :projects, :include => [ :milestones, :manager ]
      # has_and_belongs_to_many :nations, :class_name => "Country"
      # has_and_belongs_to_many :categories, :join_table => "prods_cats"
      # has_and_belongs_to_many :categories, :readonly => true
      # has_and_belongs_to_many :active_projects, :join_table => 'developers_projects', :delete_sql =>
      # "DELETE FROM developers_projects WHERE active=1 AND developer_id = #{id} AND project_id = #{record.id}"
      def has_and_belongs_to_many(name, options = {}, &extension)
        Builder::HasAndBelongsToMany.build(self, name, options, &extension)
      end
    end
  end
end
Something went wrong with that request. Please try again.