Ensures that primary_key method will return nil when multi-pk

When table has a composite primary key, the `primary_key` method for
sqlite3 and postgresql was only returning the first field of the key.

Ensures that it will return nil instead, as AR dont support composite pks.

1 files changed, 6 insertions, 0 deletions

diff --git a/activerecord/test/cases/adapters/sqlite3/sqlite3_adapter_test.rb b/activerecord/test/cases/adapters/sqlite3/sqlite3_adapter_test.rb
index 9d09ff49c7..029663e7f4 100644
--- a/activerecord/test/cases/adapters/sqlite3/sqlite3_adapter_test.rb
+++ b/activerecord/test/cases/adapters/sqlite3/sqlite3_adapter_test.rb
@@ -405,6 +405,12 @@ module ActiveRecord
         end
       end
 
+      def test_composite_primary_key
+        with_example_table 'id integer, number integer, foo integer, PRIMARY KEY (id, number)' do
+          assert_nil @conn.primary_key('ex')
+        end
+      end
+
       def test_supports_extensions
         assert_not @conn.supports_extensions?, 'does not support extensions'
       end