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@@ -4,6 +4,28 @@ module ActiveRecord
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       base.extend(ClassMethods)
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     end
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+    class HasManyAssociationStrategy
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+      def initialize(through_reflection)
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+        @through_reflection = through_reflection
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+      end
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+
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+      def primary_key
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+        if @through_reflection && @through_reflection.macro == :belongs_to
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+          @through_reflection.klass.primary_key
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+        else
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+          @through_reflection.primary_key_name
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+        end
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+      end
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+
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+      def primary_key_name
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+        if @through_reflection && @through_reflection.macro == :belongs_to
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+          @through_reflection.primary_key_name
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+        else
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+          nil
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+        end
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+      end
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+    end
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+
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     module ClassMethods
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       # Loads the named associations for the activerecord record (or records) given
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@@ -77,12 +99,13 @@ module ActiveRecord
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         end
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       end
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-      def construct_id_map(records)
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+      def construct_id_map(records, primary_key=nil)
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         id_to_record_map = {}
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         ids = []
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         records.each do |record|
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-          ids << record.id
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-          mapped_records = (id_to_record_map[record.id.to_s] ||= [])
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+          primary_key ||= record.class.primary_key
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+          ids << record[primary_key]
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+          mapped_records = (id_to_record_map[ids.last.to_s] ||= [])
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           mapped_records << record
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         end
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         ids.uniq!
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@@ -129,23 +152,24 @@ module ActiveRecord
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       end
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       def preload_has_many_association(records, reflection, preload_options={})
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-        id_to_record_map, ids = construct_id_map(records)
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-        records.each {|record| record.send(reflection.name).loaded}
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         options = reflection.options
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+        through_reflection = reflections[options[:through]]
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+        strat = HasManyAssociationStrategy.new(through_reflection)
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+        id_to_record_map, ids = construct_id_map(records, strat.primary_key_name)
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+        records.each {|record| record.send(reflection.name).loaded}
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         if options[:through]
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           through_records = preload_through_records(records, reflection, options[:through])
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           through_reflection = reflections[options[:through]]
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-          through_primary_key = through_reflection.primary_key_name
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           unless through_records.empty?
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             source = reflection.source_reflection.name
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-            #add conditions from reflection!
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-            through_records.first.class.preload_associations(through_records, source, reflection.options)
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+            through_records.first.class.preload_associations(through_records, source, options)
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             through_records.each do |through_record|
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-              add_preloaded_records_to_collection(id_to_record_map[through_record[through_primary_key].to_s],
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-                                                 reflection.name, through_record.send(source))
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+              through_record_id = through_record[strat.primary_key].to_s
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+              add_preloaded_records_to_collection(id_to_record_map[through_record_id], reflection.name, through_record.send(source))
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             end
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           end
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+
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         else
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           set_association_collection_records(id_to_record_map, reflection.name, find_associated_records(ids, reflection, preload_options),
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                                              reflection.primary_key_name)

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@@ -32,6 +32,14 @@ module ActiveRecord
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       end
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       protected
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+        def target_reflection_has_associated_record?
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+          if @reflection.through_reflection.macro == :belongs_to && @owner[@reflection.through_reflection.primary_key_name].blank?
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+            false
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+          else
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+            true
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+          end
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+        end
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+
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         def construct_find_options!(options)
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           options[:select]  = construct_select(options[:select])
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           options[:from]  ||= construct_from
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@@ -61,6 +69,7 @@ module ActiveRecord
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         end
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         def find_target
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+          return [] unless target_reflection_has_associated_record?
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           @reflection.klass.find(:all,
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             :select     => construct_select,
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             :conditions => construct_conditions,
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@@ -102,6 +111,8 @@ module ActiveRecord
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               "#{as}_type" => reflection.klass.quote_value(
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                 @owner.class.base_class.name.to_s,
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                 reflection.klass.columns_hash["#{as}_type"]) }
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+          elsif reflection.macro == :belongs_to
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+            { reflection.klass.primary_key => @owner[reflection.primary_key_name] }
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           else
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             { reflection.primary_key_name => owner_quoted_id }
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           end

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@@ -275,6 +275,15 @@ class EagerAssociationTest < ActiveRecord::TestCase
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     assert_equal authors(:david), assert_no_queries { posts_with_comments_and_author.first.author }
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   end
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+  def test_eager_with_has_many_through_a_belongs_to_association
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+    author = authors(:mary)
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+    post = Post.create!(:author => author, :title => "TITLE", :body => "BODY")
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+    author.author_favorites.create(:favorite_author_id => 1)
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+    author.author_favorites.create(:favorite_author_id => 2)
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+    posts_with_author_favorites = author.posts.find(:all, :include => :author_favorites)
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+    assert_no_queries { posts_with_author_favorites.first.author_favorites.first.author_id }
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+  end
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+
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   def test_eager_with_has_many_through_an_sti_join_model
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     author = Author.find(:first, :include => :special_post_comments, :order => 'authors.id')
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     assert_equal [comments(:does_it_hurt)], assert_no_queries { author.special_post_comments }

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@@ -1081,3 +1081,4 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
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   end
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 end
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+

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@@ -5,7 +5,7 @@ require 'models/reader'
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 require 'models/comment'
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 class HasManyThroughAssociationsTest < ActiveRecord::TestCase
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-  fixtures :posts, :readers, :people, :comments
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+  fixtures :posts, :readers, :people, :comments, :authors
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   def test_associate_existing
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     assert_queries(2) { posts(:thinking);people(:david) }
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@@ -229,4 +229,19 @@ class HasManyThroughAssociationsTest < ActiveRecord::TestCase
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       end
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     end
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   end
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+
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+  def test_has_many_association_through_a_belongs_to_association_where_the_association_doesnt_exist
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+    author = authors(:mary)
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+    post = Post.create!(:title => "TITLE", :body => "BODY")
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+    assert_equal [], post.author_favorites
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+  end
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+
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+  def test_has_many_association_through_a_belongs_to_association
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+    author = authors(:mary)
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+    post = Post.create!(:author => author, :title => "TITLE", :body => "BODY")
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+    author.author_favorites.create(:favorite_author_id => 1)
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+    author.author_favorites.create(:favorite_author_id => 2)
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+    author.author_favorites.create(:favorite_author_id => 3)
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+    assert_equal post.author.author_favorites, post.author_favorites
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+  end
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 end

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@@ -22,6 +22,8 @@ class Post < ActiveRecord::Base
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     end
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   end
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+  has_many :author_favorites, :through => :author
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+
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   has_many :comments_with_interpolated_conditions, :class_name => 'Comment',
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       :conditions => ['#{"#{aliased_table_name}." rescue ""}body = ?', 'Thank you for the welcome']
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