Fix setting inverses for composite primary key associations

Checking whether a record has a foreign key for a composite primary key
association requires us to check whether all parts of the foreign key
are present. Otherwise, the inverse association will not be set.

activerecord/lib/active_record/associations/association.rb

@@ -336,7 +336,8 @@ def invertible_for?(record)
 
         # Returns true if record contains the foreign_key
         def foreign_key_for?(record)
-          record._has_attribute?(reflection.foreign_key)
+          foreign_key = Array(reflection.foreign_key)
+          foreign_key.all? { |key| record._has_attribute?(key) }
         end
 
         # This should be implemented to return the values of the relevant key(s) on the owner,

activerecord/test/cases/associations/belongs_to_associations_test.rb

@@ -365,6 +365,17 @@ def test_building_the_belonging_object_for_composite_primary_key
     assert_equal id, cpk_book.order_id
   end
 
+  def test_belongs_to_with_inverse_association_for_composite_primary_key
+    author = Cpk::Author.new(name: "John")
+    book = author.books.build(number: 1, title: "The Rails Way")
+    order = Cpk::Order.new(book: book, status: "paid")
+    author.save!
+
+    _order_shop_id, order_id = order.id
+    assert order_id
+    assert_equal order_id, book.order_id
+  end
+
   def test_building_the_belonging_object_with_implicit_sti_base_class
     account = Account.new
     company = account.build_firm

activerecord/test/cases/associations/inverse_associations_test.rb

@@ -26,6 +26,7 @@
 require "models/subscription"
 require "models/book"
 require "models/branch"
+require "models/cpk"
 
 class AutomaticInverseFindingTests < ActiveRecord::TestCase
   fixtures :ratings, :comments, :cars, :books
@@ -602,6 +603,15 @@ def test_find_on_child_instances_with_ids_should_set_inverse_instances
     end
   end
 
+  def test_inverse_should_be_set_on_composite_primary_key_child
+    author = Cpk::Author.new(name: "John")
+    book = author.books.build(number: 1, title: "The Rails Way")
+    Cpk::Order.new(book: book, status: "paid")
+    author.save!
+
+    assert book.association(:order).loaded?
+  end
+
   def test_raise_record_not_found_error_when_invalid_ids_are_passed
     # delete all interest records to ensure that hard coded invalid_id(s)
     # are indeed invalid.