Merge pull request rails#47979 from Shopify/pm/cpk-primary-key

Extend primary key methods to support composite keys

Author: eileencodes

activerecord/lib/active_record/attribute_methods/primary_key.rb

@@ -38,17 +38,29 @@ def id=(value)
 
       # Queries the primary key column's value.
       def id?
-        query_attribute(@primary_key)
+        if self.class.composite_primary_key?
+          @primary_key.all? { |col| query_attribute(col) }
+        else
+          query_attribute(@primary_key)
+        end
       end
 
       # Returns the primary key column's value before type cast.
       def id_before_type_cast
-        attribute_before_type_cast(@primary_key)
+        if self.class.composite_primary_key?
+          @primary_key.map { |col| attribute_before_type_cast(col) }
+        else
+          attribute_before_type_cast(@primary_key)
+        end
       end
 
       # Returns the primary key column's previous value.
       def id_was
-        attribute_was(@primary_key)
+        if self.class.composite_primary_key?
+          @primary_key.map { |col| attribute_was(col) }
+        else
+          attribute_was(@primary_key)
+        end
       end
 
       # Returns the primary key column's value from the database.
@@ -61,7 +73,11 @@ def id_in_database
       end
 
       def id_for_database # :nodoc:
-        @attributes[@primary_key].value_for_database
+        if self.class.composite_primary_key?
+          @primary_key.map { |col| @attributes[col].value_for_database }
+        else
+          @attributes[@primary_key].value_for_database
+        end
       end
 
       private

activerecord/test/cases/primary_keys_test.rb

@@ -53,6 +53,24 @@ def test_to_key_with_primary_key_after_destroy
     assert_equal [1], topic.to_key
   end
 
+  def test_id_was
+    topic = Topic.find(1)
+    assert_equal 1, topic.id
+
+    topic.id = 3
+
+    assert_equal 1, topic.id_was
+    assert_equal 3, topic.id
+  end
+
+  def test_id?
+    topic = Topic.find(1)
+
+    assert_changes("topic.id?", from: true, to: false) do
+      topic.id = nil
+    end
+  end
+
   def test_integer_key
     topic = Topic.find(1)
     assert_equal(topics(:first).author_name, topic.author_name)
@@ -413,6 +431,38 @@ def test_assigning_a_non_array_value_to_model_with_composite_primary_key_raises
     end
   end
 
+  def test_id_was_composite
+    book = cpk_books(:cpk_great_author_first_book)
+    book_id = book.id
+
+    assert_not_equal [42, 42], book_id
+
+    book.id = [42, 42]
+
+    assert_equal book_id, book.id_was
+    assert_equal [42, 42], book.id
+  end
+
+  def test_id_predicate_composite
+    book = cpk_books(:cpk_great_author_first_book)
+
+    valid_id = [42, 42]
+
+    invalid_ids = [
+      [42, nil],
+      [nil, 42],
+      [nil, nil],
+    ]
+
+    invalid_ids.each do |invalid_id|
+      book.id = valid_id
+
+      assert_changes("book.id?", from: true, to: false) do
+        book.id = invalid_id
+      end
+    end
+  end
+
   def test_primary_key_issues_warning
     model = Class.new(ActiveRecord::Base) do
       def self.table_name