- Calling fetchone() or similar on a result that

has already been exhausted, has been closed,
or is not a result-returning result now
raises ResourceClosedError, a subclass of
InvalidRequestError, in all cases, regardless
of backend.  Previously, some DBAPIs would
raise ProgrammingError (i.e. pysqlite), others
would return None leading to downstream breakages
(i.e. MySQL-python).

- Connection, ResultProxy, as well as Session use
ResourceClosedError for all "this
connection/transaction/result is closed" types of
errors.

4 files changed, 38 insertions, 11 deletions

diff --git a/lib/sqlalchemy/dialects/sqlite/base.py b/lib/sqlalchemy/dialects/sqlite/base.py
index 2d9e56baf..b84b18e68 100644
--- a/lib/sqlalchemy/dialects/sqlite/base.py
+++ b/lib/sqlalchemy/dialects/sqlite/base.py
@@ -600,5 +600,5 @@ def _pragma_cursor(cursor):
     """work around SQLite issue whereby cursor.description is blank when PRAGMA returns no rows."""
     
     if cursor.closed:
-        cursor._fetchone_impl = lambda: None
+        cursor.fetchone = lambda: None
     return cursor
diff --git a/lib/sqlalchemy/engine/base.py b/lib/sqlalchemy/engine/base.py
index cf459f9e6..684df51ca 100644
--- a/lib/sqlalchemy/engine/base.py
+++ b/lib/sqlalchemy/engine/base.py
@@ -908,7 +908,7 @@ class Connection(Connectable):
                 self.__connection = self.engine.raw_connection()
                 self.__invalid = False
                 return self.__connection
-            raise exc.InvalidRequestError("This Connection is closed")
+            raise exc.ResourceClosedError("This Connection is closed")
 
     @property
     def info(self):
@@ -956,7 +956,7 @@ class Connection(Connectable):
         """
 
         if self.closed:
-            raise exc.InvalidRequestError("This Connection is closed")
+            raise exc.ResourceClosedError("This Connection is closed")
 
         if self.__connection.is_valid:
             self.__connection.invalidate(exception)
@@ -2279,7 +2279,9 @@ class ResultProxy(object):
             if _autoclose_connection and \
                 self.connection.should_close_with_result:
                 self.connection.close()
-
+            # allow consistent errors
+            self.cursor = None
+            
     def __iter__(self):
         while True:
             row = self.fetchone()
@@ -2361,14 +2363,32 @@ class ResultProxy(object):
         return self.dialect.supports_sane_multi_rowcount
 
     def _fetchone_impl(self):
-        return self.cursor.fetchone()
+        try:
+            return self.cursor.fetchone()
+        except AttributeError:
+            self._non_result()
 
     def _fetchmany_impl(self, size=None):
-        return self.cursor.fetchmany(size)
+        try:
+            return self.cursor.fetchmany(size)
+        except AttributeError:
+            self._non_result()
 
     def _fetchall_impl(self):
-        return self.cursor.fetchall()
-
+        try:
+            return self.cursor.fetchall()
+        except AttributeError:
+            self._non_result()
+    
+    def _non_result(self):
+        if self._metadata is None:
+            raise exc.ResourceClosedError(
+            "This result object does not return rows. "
+            "It has been closed automatically.",
+            )
+        else:
+            raise exc.ResourceClosedError("This result object is closed.")
+        
     def process_rows(self, rows):
         process_row = self._process_row
         metadata = self._metadata
@@ -2425,7 +2445,6 @@ class ResultProxy(object):
         Else the cursor is automatically closed and None is returned.
         
         """
-
         try:
             row = self._fetchone_impl()
             if row is not None:
@@ -2445,6 +2464,9 @@ class ResultProxy(object):
         Returns None if no row is present.
         
         """
+        if self._metadata is None:
+            self._non_result()
+
         try:
             row = self._fetchone_impl()
         except Exception, e:
diff --git a/lib/sqlalchemy/exc.py b/lib/sqlalchemy/exc.py
index 31826f44f..1c412824c 100644
--- a/lib/sqlalchemy/exc.py
+++ b/lib/sqlalchemy/exc.py
@@ -60,6 +60,10 @@ class InvalidRequestError(SQLAlchemyError):
 
     """
 
+class ResourceClosedError(InvalidRequestError):
+    """An operation was requested from a connection, cursor, or other
+    object that's in a closed state."""
+    
 class NoSuchColumnError(KeyError, InvalidRequestError):
     """A nonexistent column is requested from a ``RowProxy``."""
 
diff --git a/lib/sqlalchemy/orm/session.py b/lib/sqlalchemy/orm/session.py
index d092375a6..8516a22de 100644
--- a/lib/sqlalchemy/orm/session.py
+++ b/lib/sqlalchemy/orm/session.py
@@ -235,7 +235,7 @@ class SessionTransaction(object):
 
     def _assert_is_open(self, error_msg="The transaction is closed"):
         if self.session is None:
-            raise sa_exc.InvalidRequestError(error_msg)
+            raise sa_exc.ResourceClosedError(error_msg)
 
     @property
     def _is_transaction_boundary(self):
@@ -427,7 +427,8 @@ class SessionTransaction(object):
         return self
 
     def __exit__(self, type, value, traceback):
-        self._assert_is_open("Cannot end transaction context. The transaction was closed from within the context")
+        self._assert_is_open("Cannot end transaction context. The transaction "
+                                    "was closed from within the context")
         if self.session.transaction is None:
             return
         if type is None: