Merge pull request #15309 from iantropov/issue_12698_build_through

Add setting of FK for throgh associations while building

Conflicts:
	activerecord/CHANGELOG.md
	activerecord/test/cases/associations/has_many_through_associations_test.rb

4 files changed, 29 insertions, 1 deletions

diff --git a/activerecord/CHANGELOG.md b/activerecord/CHANGELOG.md
index 64e3890b76..b78adba732 100644
--- a/activerecord/CHANGELOG.md
+++ b/activerecord/CHANGELOG.md
@@ -1,3 +1,9 @@
+*   Fixed setting of foreign_key for through associations while building of new record.
+
+    Fixes #12698.
+
+    *Ivan Antropov*
+
 *   Improve a dump of the primary key support. If it is not a default primary key,
     correctly dump the type and options.
 
diff --git a/activerecord/lib/active_record/associations/through_association.rb b/activerecord/lib/active_record/associations/through_association.rb
index e47e81aa0f..09828dbd9b 100644
--- a/activerecord/lib/active_record/associations/through_association.rb
+++ b/activerecord/lib/active_record/associations/through_association.rb
@@ -91,6 +91,17 @@ module ActiveRecord
             raise HasManyThroughNestedAssociationsAreReadonly.new(owner, reflection)
           end
         end
+
+        def build_record(attributes)
+          inverse = source_reflection.inverse_of
+          target = through_association.target
+
+          if inverse && target && !target.is_a?(Array)
+            attributes[inverse.foreign_key] = target.id
+          end
+
+          super(attributes)
+        end
     end
   end
 end
diff --git a/activerecord/test/cases/associations/has_many_through_associations_test.rb b/activerecord/test/cases/associations/has_many_through_associations_test.rb
index 589a232bdb..6729a5a9fc 100644
--- a/activerecord/test/cases/associations/has_many_through_associations_test.rb
+++ b/activerecord/test/cases/associations/has_many_through_associations_test.rb
@@ -25,12 +25,13 @@ require 'models/categorization'
 require 'models/member'
 require 'models/membership'
 require 'models/club'
+require 'models/organization'
 
 class HasManyThroughAssociationsTest < ActiveRecord::TestCase
   fixtures :posts, :readers, :people, :comments, :authors, :categories, :taggings, :tags,
            :owners, :pets, :toys, :jobs, :references, :companies, :members, :author_addresses,
            :subscribers, :books, :subscriptions, :developers, :categorizations, :essays,
-           :categories_posts, :clubs, :memberships
+           :categories_posts, :clubs, :memberships, :organizations
 
   # Dummies to force column loads so query counts are clean.
   def setup
@@ -1151,4 +1152,12 @@ class HasManyThroughAssociationsTest < ActiveRecord::TestCase
     club.members << member
     assert_equal 1, SuperMembership.where(member_id: member.id, club_id: club.id).count
   end
+
+  def test_build_for_has_many_through_association
+    organization = organizations(:nsa)
+    author = organization.author
+    post_direct = author.posts.build
+    post_through = organization.posts.build
+    assert_equal post_direct.author_id, post_through.author_id
+  end
 end
diff --git a/activerecord/test/models/organization.rb b/activerecord/test/models/organization.rb
index 72e7bade68..f3e92f3067 100644
--- a/activerecord/test/models/organization.rb
+++ b/activerecord/test/models/organization.rb
@@ -8,5 +8,7 @@ class Organization < ActiveRecord::Base
   has_one :author, :primary_key => :name
   has_one :author_owned_essay_category, :through => :author, :source => :owned_essay_category
 
+  has_many :posts, :through => :author, :source => :posts
+
   scope :clubs, -> { from('clubs') }
 end