Import PyMySQL bugfix #649 (#313)

* Pulled test from PyMySQL cf1c74c213eebeaad706a7bc53d729c9ddbb54fd

* Imported PyMySQL changes to fix nextset bug

aiomysql/connection.py

@@ -589,6 +589,7 @@ def _write_bytes(self, data):
         return self._writer.write(data)
 
     async def _read_query_result(self, unbuffered=False):
+        self._result = None
         if unbuffered:
             try:
                 result = MySQLResult(self)

aiomysql/cursors.py

@@ -184,6 +184,8 @@ async def nextset(self):
             return
         if not current_result.has_next:
             return
+        self._result = None
+        self._clear_result()
         await conn.next_result()
         await self._do_get_result()
         return True
@@ -449,9 +451,19 @@ def scroll(self, value, mode='relative'):
     async def _query(self, q):
         conn = self._get_db()
         self._last_executed = q
+        self._clear_result()
         await conn.query(q)
         await self._do_get_result()
 
+    def _clear_result(self):
+        self._rownumber = 0
+        self._result = None
+
+        self._rowcount = 0
+        self._description = None
+        self._lastrowid = None
+        self._rows = None
+
     async def _do_get_result(self):
         conn = self._get_db()
         self._rownumber = 0

tests/test_nextset.py

@@ -1,4 +1,7 @@
+import asyncio
+
 import pytest
+from pymysql.err import ProgrammingError
 
 
 @pytest.mark.run_loop
@@ -27,6 +30,15 @@ async def test_skip_nextset(cursor):
     assert [(42,)] == list(r)
 
 
+@pytest.mark.run_loop
+async def test_nextset_error(cursor):
+    await cursor.execute("SELECT 1; xyzzy;")
+
+    # nextset shouldn't hang on error, it should raise syntax error
+    with pytest.raises(ProgrammingError):
+        await asyncio.wait_for(cursor.nextset(), 5)
+
+
 @pytest.mark.run_loop
 async def test_ok_and_next(cursor):
     await cursor.execute("SELECT 1; commit; SELECT 2;")