Merge pull request rails#47720 from Shopify/pm/cpk-id-accessor

Accept composite primary key in `id=`

Author: eileencodes

activerecord/lib/active_record/attribute_methods/primary_key.rb

@@ -23,7 +23,11 @@ def id
 
       # Sets the primary key column's value.
       def id=(value)
-        _write_attribute(@primary_key, value)
+        if self.class.composite_primary_key?
+          @primary_key.zip(value) { |attr, value| _write_attribute(attr, value) }
+        else
+          _write_attribute(@primary_key, value)
+        end
       end
 
       # Queries the primary key column's value.

activerecord/test/cases/primary_keys_test.rb

@@ -373,6 +373,22 @@ def test_composite_primary_key_out_of_order
     assert_equal ["code", "region"], @connection.primary_keys("barcodes_reverse")
   end
 
+  def test_assigning_a_composite_primary_key
+    book = Cpk::Book.new
+    book.id = [1, 2]
+    book.save!
+
+    assert_equal [1, 2], book.id
+  end
+
+  def test_assigning_a_non_array_value_to_model_with_composite_primary_key_raises
+    book = Cpk::Book.new
+
+    assert_raises(TypeError) do
+      book.id = 1
+    end
+  end
+
   def test_primary_key_issues_warning
     model = Class.new(ActiveRecord::Base) do
       def self.table_name