Add support for nullifying CPK has_one associations

Composite primary key records need to conditionally unset multiple
column attributes from the associated record in order to properly
support dependent: nullify.

activerecord/lib/active_record/associations/has_one_association.rb

@@ -121,7 +121,9 @@ module ActiveRecord
         end
 
         def nullify_owner_attributes(record)
-          record[reflection.foreign_key] = nil
+          Array(reflection.foreign_key).each do |foreign_key_column|
+            record[foreign_key_column] = nil unless foreign_key_column.in?(Array(record.class.primary_key))
+          end
         end
 
         def transaction_if(value, &block)

activerecord/test/cases/associations/has_one_associations_test.rb

@@ -145,6 +145,28 @@ class HasOneAssociationsTest < ActiveRecord::TestCase
     assert_not_predicate developer, :persisted?
   end
 
+  def test_nullification_on_cpk_association
+    book = Cpk::Book.create!(author_id: 1, number: 2)
+    other_book = Cpk::Book.create!(author_id: 3, number: 4)
+    order = Cpk::OrderWithNullifiedBook.create!(book: book)
+
+    order.book = other_book
+
+    assert_nil book.order_id
+    assert_nil book.shop_id
+  end
+
+  def test_nullification_on_cpk_association_with_pk_column
+    chapter = Cpk::Chapter.create!(author_id: 1, number: 2)
+    other_chapter = Cpk::Chapter.create!(author_id: 1, number: 4)
+    book = Cpk::NullifiedBook.create!(chapter: chapter, number: 1, author_id: 1)
+
+    book.chapter = other_chapter
+
+    assert_nil chapter.book_number
+    assert_not_nil chapter.author_id
+  end
+
   def test_natural_assignment_to_nil_after_destroy
     firm = companies(:rails_core)
     old_account_id = firm.account.id

activerecord/test/models/cpk.rb

@@ -7,3 +7,4 @@ require_relative "cpk/review"
 require_relative "cpk/order_agreement"
 require_relative "cpk/order_tag"
 require_relative "cpk/tag"
+require_relative "cpk/chapter"

activerecord/test/models/cpk/book.rb

@@ -6,6 +6,8 @@ module Cpk
 
     belongs_to :order, autosave: true, query_constraints: [:shop_id, :order_id]
     belongs_to :author, class_name: "Cpk::Author"
+
+    has_many :chapters, query_constraints: [:author_id, :book_number]
   end
 
   class BestSeller < Book
@@ -14,4 +16,8 @@ module Cpk
   class BrokenBook < Book
     belongs_to :order
   end
+
+  class NullifiedBook < Book
+    has_one :chapter, query_constraints: [:author_id, :book_number], dependent: :nullify
+  end
 end

activerecord/test/models/cpk/chapter.rb

@@ -0,0 +1,12 @@
+# frozen_string_literal: true
+
+module Cpk
+  class Chapter < ActiveRecord::Base
+    self.table_name = :cpk_chapters
+    # explicit definition is to allow schema definition to be simplified
+    # to be shared between different databases
+    self.primary_key = [:author_id, :number]
+
+    belongs_to :book, query_constraints: [:author_id, :book_number]
+  end
+end

activerecord/test/models/cpk/order.rb

@@ -20,4 +20,8 @@ module Cpk
   class OrderWithPrimaryKeyAssociatedBook < Order
     has_one :book, primary_key: :id, foreign_key: :order_id
   end
+
+  class OrderWithNullifiedBook < Order
+    has_one :book, query_constraints: [:shop_id, :order_id], dependent: :nullify
+  end
 end

activerecord/test/schema/schema.rb

@@ -249,6 +249,13 @@ ActiveRecord::Schema.define do
     t.integer :shop_id
   end
 
+  create_table :cpk_chapters, primary_key: [:author_id, :number], force: true do |t|
+    t.integer :author_id
+    t.integer :number
+    t.integer :book_number
+    t.string :title
+  end
+
   create_table :cpk_authors, force: true do |t|
     t.string :name
   end