fix: allow cursors in external transactions (#1350)

Author: aryansk

asyncpg/cursor.py

@@ -111,7 +111,7 @@ def _check_ready(self):
             raise exceptions.InterfaceError(
                 'cursor: the prepared statement is closed')
 
-        if not self._connection._top_xact:
+        if not self._connection.is_in_transaction():
             raise exceptions.NoActiveSQLTransactionError(
                 'cursor cannot be created outside of a transaction')
 

tests/test_cursor.py

@@ -109,6 +109,17 @@ async def test_cursor_01(self):
                                     'cursor cannot be created.*transaction'):
             await st.cursor()
 
+    async def test_cursor_external_transaction(self):
+        await self.con.execute('BEGIN')
+        try:
+            st = await self.con.prepare('SELECT generate_series(0, 2)')
+            cur = await st.cursor()
+            self.assertEqual(
+                await cur.fetch(10),
+                [(0,), (1,), (2,)])
+        finally:
+            await self.con.execute('ROLLBACK')
+
     async def test_cursor_02(self):
         st = await self.con.prepare('SELECT generate_series(0, 20)')
         async with self.con.transaction():