Do not crash on PREPARE statements

Just handle the result set.
Leave the id of the prepared statement in cursor.lastrowid
so it can be used with EXEC.

See also issue #116.

pymonetdb/sql/cursors.py

@@ -346,7 +346,7 @@ def _store_result(self, block):  # noqa: C901
                 logger.info(line[1:])
                 self.messages.append((Warning, line[1:]))
 
-            elif line.startswith(mapi.MSG_QTABLE):
+            elif line.startswith(mapi.MSG_QTABLE) or line.startswith(mapi.MSG_QPREPARE):
                 self._query_id, rowcount, columns, tuples = line[2:].split()[:4]
 
                 columns = int(columns)  # number of columns in result
@@ -368,7 +368,10 @@ def _store_result(self, block):  # noqa: C901
                 # typesizes = [(0, 0)] * columns
 
                 self._offset = 0
-                self.lastrowid = None
+                if line.startswith(mapi.MSG_QPREPARE):
+                    self.lastrowid = int(self._query_id)
+                else:
+                    self.lastrowid = None
 
             elif line.startswith(mapi.MSG_HEADER):
                 (data, identity) = line[1:].split("#")
@@ -401,7 +404,6 @@ def _store_result(self, block):  # noqa: C901
                                                    precision[i], scale[i], null_ok[i]))
                 self.description = description
                 self._offset = 0
-                self.lastrowid = None
 
             elif line.startswith(mapi.MSG_TUPLE):
                 values = self._parse_tuple(line)

tests/test_prepare.py

@@ -0,0 +1,29 @@
+from unittest import TestCase
+from pymonetdb import connect
+from tests.util import test_args
+
+
+class TestPrepare(TestCase):
+    def setUp(self):
+        self.connection = connect(autocommit=False, **test_args)
+        self.cursor = self.connection.cursor()
+
+    def test_prepare(self):
+        # It would be nice to have a prepare API but in the mean time we can
+        # invoke PREPARE and EXEC ourselves.
+        #
+        # Note how the id of the newly prepared statement is stashed in
+        # cursor.lastrowid.
+
+        prepare = "PREPARE SELECT value, 10 * value, 100 * value FROM sys.generate_series(0, ?)"
+        self.cursor.execute(prepare)
+        exec_id = self.cursor.lastrowid
+
+        n = 3
+        expected = [
+            (value, 10 * value, 100 * value)
+            for value in range(n)
+        ]
+        self.cursor.execute("EXEC %s(%s)", (exec_id, n))
+        received = self.cursor.fetchall()
+        self.assertEqual(expected, received)