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.

3 files changed, 18 insertions, 0 deletions

diff --git a/activerecord/test/cases/adapters/mysql/mysql_adapter_test.rb b/activerecord/test/cases/adapters/mysql/mysql_adapter_test.rb
index 28106d3772..85db8f4614 100644
--- a/activerecord/test/cases/adapters/mysql/mysql_adapter_test.rb
+++ b/activerecord/test/cases/adapters/mysql/mysql_adapter_test.rb
@@ -99,6 +99,12 @@ module ActiveRecord
         end
       end
 
+      def test_composite_primary_key
+        with_example_table '`id` INT(11), `number` INT(11), foo INT(11), PRIMARY KEY (`id`, `number`)' do
+          assert_nil @conn.primary_key('ex')
+        end
+      end
+
       def test_tinyint_integer_typecasting
         with_example_table '`status` TINYINT(4)' do
           insert(@conn, { 'status' => 2 }, 'ex')
diff --git a/activerecord/test/cases/adapters/postgresql/postgresql_adapter_test.rb b/activerecord/test/cases/adapters/postgresql/postgresql_adapter_test.rb
index c3c696b871..6bb2b26cd5 100644
--- a/activerecord/test/cases/adapters/postgresql/postgresql_adapter_test.rb
+++ b/activerecord/test/cases/adapters/postgresql/postgresql_adapter_test.rb
@@ -54,6 +54,12 @@ module ActiveRecord
         end
       end
 
+      def test_composite_primary_key
+        with_example_table 'id serial, number serial, PRIMARY KEY (id, number)' do
+          assert_nil @connection.primary_key('ex')
+        end
+      end
+
       def test_primary_key_raises_error_if_table_not_found
         assert_raises(ActiveRecord::StatementInvalid) do
           @connection.primary_key('unobtainium')
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