I have a problem merging a polymorphic persistent object. Please read
my description of the problem below. Sorry if it's a little complex.
I've got a polymorphic mapper defined as so:
sqlalchemy.orm.mapper(Generic, generics_table,
polymorphic_on=generics_table.c.type,
polymorphic_identity='generic')
sqlalchemy.orm.mapper(Specific, specifics_table,
inherits=Generic, polymorphic_identity='specific')
I query a Specific instance like this:
specific = session.query(Generic).get(specific_key)
The attributes stored in 'specifics_table' are not loaded from the DB
until they are accessed (lazy-loaded).
I serialize the Specific instance and send it to the client without
lazy-loading the 'specifics_table' attributes.
The client alters the Specific instance and sends it back to the
server to save. The de-serialized Specific instance is of type
Specific, but does not have any attributes from
'specifics_table' (since they were never loaded from the DB).
I use merge to save the altered Specific instance that came from the
client:
merged_obj = session.merge(specific)
session.commit()
In versions prior to 0.5.0 this data flow worked fine. After upgrading
to 0.5.0 I get an exception with the following trace.
It looks like SA is trying to update the sub-class, but there aren't
any attributes to update, since all sub-class specific attributes are
missing from the object, so it is generating bad SQL. Is this a bug,
or do I need to change something to be compatible with 0.5.0?
Error: ProgrammingError -
-
Description: (ProgrammingError) syntax error at or near "WHERE" at
character 34
'UPDATE specifics_table SET WHERE specifics_table.generic_id =
%(specifics_table_generic_id)s' {'specifics_table_generic_id':
2} -
-
Traceback: File "app.py",
...app trace cut for brevity...
session.flush()
-
File
"/usr/local/lib/python2.5/site-packages/SQLAlchemy-0.5.0-py2.5.egg/
sqlalchemy/orm/session.py",
line 1349, in flush
self._flush(objects)
-
File
"/usr/local/lib/python2.5/site-packages/SQLAlchemy-0.5.0-py2.5.egg/
sqlalchemy/orm/session.py",
line 1419, in _flush
flush_context.execute()
-
File
"/usr/local/lib/python2.5/site-packages/SQLAlchemy-0.5.0-py2.5.egg/
sqlalchemy/orm/unitofwork.py",
line 260, in execute
UOWExecutor().execute(self, tasks)
-
File
"/usr/local/lib/python2.5/site-packages/SQLAlchemy-0.5.0-py2.5.egg/
sqlalchemy/orm/unitofwork.py",
line 723, in execute
self.execute_save_steps(trans, task)
-
File
"/usr/local/lib/python2.5/site-packages/SQLAlchemy-0.5.0-py2.5.egg/
sqlalchemy/orm/unitofwork.py",
line 738, in execute_save_steps
self.save_objects(trans, task)
-
File
"/usr/local/lib/python2.5/site-packages/SQLAlchemy-0.5.0-py2.5.egg/
sqlalchemy/orm/unitofwork.py",
line 729, in save_objects
task.mapper._save_obj(task.polymorphic_tosave_objects, trans)
-
File
"/usr/local/lib/python2.5/site-packages/SQLAlchemy-0.5.0-py2.5.egg/
sqlalchemy/orm/mapper.py",
line 1358, in _save_obj
c = connection.execute(statement.values(value_params), params)
-
File
"/usr/local/lib/python2.5/site-packages/SQLAlchemy-0.5.0-py2.5.egg/
sqlalchemy/engine/base.py",
line 824, in execute
return Connection.executors[c](self, object, multiparams, params)
-
File
"/usr/local/lib/python2.5/site-packages/SQLAlchemy-0.5.0-py2.5.egg/
sqlalchemy/engine/base.py",
line 874, in _execute_clauseelement
return self.__execute_context(context)
-
File
"/usr/local/lib/python2.5/site-packages/SQLAlchemy-0.5.0-py2.5.egg/
sqlalchemy/engine/base.py",
line 896, in __execute_context
self._cursor_execute(context.cursor, context.statement,
context.parameters[0], context=context)
-
File
"/usr/local/lib/python2.5/site-packages/SQLAlchemy-0.5.0-py2.5.egg/
sqlalchemy/engine/base.py",
line 950, in _cursor_execute
self._handle_dbapi_exception(e, statement, parameters, cursor,
context)
-
File
"/usr/local/lib/python2.5/site-packages/SQLAlchemy-0.5.0-py2.5.egg/
sqlalchemy/engine/base.py",
line 931, in _handle_dbapi_exception
raise exc.DBAPIError.instance(statement, parameters, e,
connection_invalidated=is_disconnect)
Any help would be greatly appreciated.
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