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Allow building and then later saving has_many :through records, such …

…that the join record is automatically saved too. This requires the :inverse_of option to be set on the source association in the join model. See the CHANGELOG for details. [#4329 state:resolved]
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1 parent f0b9805 commit 91fd6510563f84ee473bb217bc63ed598abe3f24 @jonleighton jonleighton committed Feb 14, 2011
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24 activerecord/CHANGELOG
@@ -1,5 +1,29 @@
*Rails 3.1.0 (unreleased)*
+* Make has_many :through associations work correctly when you build a record and then save it. This
+ requires you to set the :inverse_of option on the source reflection on the join model, like so:
+
+ class Post < ActiveRecord::Base
+ has_many :taggings
+ has_many :tags, :through => :taggings
+ end
+
+ class Tagging < ActiveRecord::Base
+ belongs_to :post
+ belongs_to :tag, :inverse_of => :tagging # :inverse_of must be set!
+ end
+
+ class Tag < ActiveRecord::Base
+ has_many :taggings
+ has_many :posts, :through => :taggings
+ end
+
+ post = Post.first
+ tag = post.tags.build :name => "ruby"
+ tag.save # will save a Taggable linking to the post
+
+ [Jon Leighton]
+
* Support the :dependent option on has_many :through associations. For historical and practical
reasons, :delete_all is the default deletion strategy employed by association.delete(*records),
despite the fact that the default strategy is :nullify for regular has_many. Also, this only
View
38 activerecord/lib/active_record/associations.rb
@@ -523,6 +523,22 @@ def association_instance_set(name, association)
# @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
+ #
# === Polymorphic Associations
#
# Polymorphic associations on models are not restricted on what types of models they
@@ -1043,13 +1059,21 @@ module ClassMethods
# [:as]
# Specifies a polymorphic interface (See <tt>belongs_to</tt>).
# [:through]
- # Specifies a join model through which to perform the query. Options for <tt>:class_name</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>belongs_to</tt>, <tt>has_one</tt>
- # or <tt>has_many</tt> association on the join model. The collection of join models
- # can be managed via the collection API. For example, new join models are created for
- # newly associated objects, and if some are gone their rows are deleted (directly,
- # no destroy callbacks are triggered).
+ # 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>belongs_to</tt>,
+ # <tt>has_one</tt> or <tt>has_many</tt> association on the join model.
+ #
+ # 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.
View
50 activerecord/lib/active_record/associations/has_many_through_association.rb
@@ -37,16 +37,44 @@ def <<(*records)
def insert_record(record, validate = true)
return if record.new_record? && !record.save(:validate => validate)
-
- through_association = @owner.send(@reflection.through_reflection.name)
- through_association.create!(construct_join_attributes(record))
-
+ through_record(record).save!
update_counter(1)
record
end
private
+ def through_record(record)
+ through_association = @owner.send(:association_proxy, @reflection.through_reflection.name)
+ attributes = construct_join_attributes(record)
+
+ through_record = Array.wrap(through_association.target).find { |candidate|
+ candidate.attributes.slice(*attributes.keys) == attributes
+ }
+
+ unless through_record
+ through_record = through_association.build(attributes)
+ through_record.send("#{@reflection.source_reflection.name}=", record)
+ end
+
+ through_record
+ end
+
+ def build_record(attributes)
+ record = super(attributes)
+
+ inverse = @reflection.source_reflection.inverse_of
+ if inverse
+ if inverse.macro == :has_many
+ record.send(inverse.name) << through_record(record)
+ elsif inverse.macro == :has_one
+ record.send("#{inverse.name}=", through_record(record))
+ end
+ end
+
+ record
+ end
+
def target_reflection_has_associated_record?
if @reflection.through_reflection.macro == :belongs_to && @owner[@reflection.through_reflection.foreign_key].blank?
false
@@ -79,13 +107,27 @@ def delete_records(records, method)
count = scope.delete_all
end
+ delete_through_records(through, records)
+
if @reflection.through_reflection.macro == :has_many && update_through_counter?(method)
update_counter(-count, @reflection.through_reflection)
end
update_counter(-count)
end
+ def delete_through_records(through, records)
+ if @reflection.through_reflection.macro == :has_many
+ records.each do |record|
+ through.target.delete(through_record(record))
+ end
+ else
+ records.each do |record|
+ through.target = nil if through.target == through_record(record)
+ end
+ end
+ end
+
def find_target
return [] unless target_reflection_has_associated_record?
scoped.all
View
18 activerecord/test/cases/associations/has_many_through_associations_test.rb
@@ -113,6 +113,24 @@ def test_associate_new_by_building
assert posts(:thinking).reload.people(true).collect(&:first_name).include?("Ted")
end
+ def test_build_then_save_with_has_many_inverse
+ post = posts(:thinking)
+ person = post.people.build(:first_name => "Bob")
+ person.save
+ post.reload
+
+ assert post.people.include?(person)
+ end
+
+ def test_build_then_save_with_has_one_inverse
+ post = posts(:thinking)
+ person = post.single_people.build(:first_name => "Bob")
+ person.save
+ post.reload
+
+ assert post.single_people.include?(person)
+ end
+
def test_delete_association
assert_queries(2){posts(:welcome);people(:michael); }
View
2 activerecord/test/models/person.rb
@@ -1,5 +1,7 @@
class Person < ActiveRecord::Base
has_many :readers
+ has_one :reader
+
has_many :posts, :through => :readers
has_many :posts_with_no_comments, :through => :readers, :source => :post, :include => :comments, :conditions => 'comments.id is null'
View
1 activerecord/test/models/post.rb
@@ -95,6 +95,7 @@ def add_joins_and_select
has_many :readers
has_many :readers_with_person, :include => :person, :class_name => "Reader"
has_many :people, :through => :readers
+ has_many :single_people, :through => :readers
has_many :people_with_callbacks, :source=>:person, :through => :readers,
:before_add => lambda {|owner, reader| log(:added, :before, reader.first_name) },
:after_add => lambda {|owner, reader| log(:added, :after, reader.first_name) },
View
3 activerecord/test/models/reader.rb
@@ -1,4 +1,5 @@
class Reader < ActiveRecord::Base
belongs_to :post
- belongs_to :person
+ belongs_to :person, :inverse_of => :readers
+ belongs_to :single_person, :class_name => 'Person', :foreign_key => :person_id, :inverse_of => :reader
end

4 comments on commit 91fd651

@geoffgarside

Is there any chance this commit can be included in next v3.0.x release?

@philevans

I agree - I really could do with having this included in the next release. Pretty please with sugar on?

@jonleighton
Ruby on Rails member

Hiya, the associations code has been pretty much rewritten in master, so it would be non-trivial to port this to 3-0-stable. Also, we don't add new features to the stable branch, only bug fixes. So the answer is no, sorry.

@geoffgarside

Ta, heres looking forward to 3.1 then

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