I'm writing an application using Turbogears and I'm migrating it from
SQLObject to Elixir/SQLAlchemy. I have declared an Item class which
has an amount. I want the Item to be deleted if the amount goes to 0.
class Item(Entity):
id = Field(Integer, primary_key=True)
itemType = ManyToOne('ItemType')
amount = Field(Integer)
quality = Field(Integer)
...a bunch of ManyToOne relationships
def SubtractAmount(self, amount):
self.amount -= amount
if self.amount == 0:
self = None # was self.destroySelf() using SQLObject
return
After anItem.SubtractAmount(anItem.amount) is called, I get the
following error:
Page handler: <bound method Root.ToonTrade of <mg1.controllers.Root
object at 0x01E6FF10>>
Traceback (most recent call last):
File "c:\python25\lib\site-packages\cherrypy-2.3.0-py2.5.egg\cherrypy
\_cphttptools.py", line 121, in _run
self.main()
File "c:\python25\lib\site-packages\cherrypy-2.3.0-py2.5.egg\cherrypy
\_cphttptools.py", line 264, in main
body = page_handler(*virtual_path, **self.params)
File "<string>", line 3, in ToonTrade
File "c:\python25\lib\site-packages\TurboGears-1.0.5-py2.5.egg
\turbogears\controllers.py", line 359, in expose
*args, **kw)
File "<string>", line 5, in run_with_transaction
File "c:\python25\lib\site-packages\TurboGears-1.0.5-py2.5.egg
\turbogears\database.py", line 434, in sa_rwt
session.commit()
File "c:\python25\lib\site-packages\SQLAlchemy-0.4.7-py2.5.egg
\sqlalchemy\orm\scoping.py", line 98, in do
return getattr(self.registry(), name)(*args, **kwargs)
File "c:\python25\lib\site-packages\SQLAlchemy-0.4.7-py2.5.egg
\sqlalchemy\orm\session.py", line 557, in commit
self.transaction.commit()
File "c:\python25\lib\site-packages\SQLAlchemy-0.4.7-py2.5.egg
\sqlalchemy\orm\session.py", line 262, in commit
self._prepare_impl()
File "c:\python25\lib\site-packages\SQLAlchemy-0.4.7-py2.5.egg
\sqlalchemy\orm\session.py", line 246, in _prepare_impl
self.session.flush()
File "c:\python25\lib\site-packages\SQLAlchemy-0.4.7-py2.5.egg
\sqlalchemy\orm\session.py", line 789, in flush
self.uow.flush(self, objects)
File "c:\python25\lib\site-packages\SQLAlchemy-0.4.7-py2.5.egg
\sqlalchemy\orm\unitofwork.py", line 233, in flush
flush_context.execute()
File "c:\python25\lib\site-packages\SQLAlchemy-0.4.7-py2.5.egg
\sqlalchemy\orm\unitofwork.py", line 445, in execute
UOWExecutor().execute(self, tasks)
File "c:\python25\lib\site-packages\SQLAlchemy-0.4.7-py2.5.egg
\sqlalchemy\orm\unitofwork.py", line 930, in execute
self.execute_save_steps(trans, task)
File "c:\python25\lib\site-packages\SQLAlchemy-0.4.7-py2.5.egg
\sqlalchemy\orm\unitofwork.py", line 945, in execute_save_steps
self.save_objects(trans, task)
File "c:\python25\lib\site-packages\SQLAlchemy-0.4.7-py2.5.egg
\sqlalchemy\orm\unitofwork.py", line 936, in save_objects
task.mapper._save_obj(task.polymorphic_tosave_objects, trans)
File "c:\python25\lib\site-packages\SQLAlchemy-0.4.7-py2.5.egg
\sqlalchemy\orm\mapper.py", line 1161, in _save_obj
c = connection.execute(statement.values(value_params), params)
File "c:\python25\lib\site-packages\SQLAlchemy-0.4.7-py2.5.egg
\sqlalchemy\engine\base.py", line 844, in execute
return Connection.executors[c](self, object, multiparams, params)
File "c:\python25\lib\site-packages\SQLAlchemy-0.4.7-py2.5.egg
\sqlalchemy\engine\base.py", line 895, in execute_clauseelement
return self._execute_compiled(elem.compile(dialect=self.dialect,
column_keys=keys, inline=len(params) > 1), distilled_params=params)
File "c:\python25\lib\site-packages\SQLAlchemy-0.4.7-py2.5.egg
\sqlalchemy\engine\base.py", line 907, in _execute_compiled
self.__execute_raw(context)
File "c:\python25\lib\site-packages\SQLAlchemy-0.4.7-py2.5.egg
\sqlalchemy\engine\base.py", line 916, in __execute_raw
self._cursor_execute(context.cursor, context.statement,
context.parameters[0], context=context)
File "c:\python25\lib\site-packages\SQLAlchemy-0.4.7-py2.5.egg
\sqlalchemy\engine\base.py", line 960, in _cursor_execute
self._handle_dbapi_exception(e, statement, parameters, cursor)
File "c:\python25\lib\site-packages\SQLAlchemy-0.4.7-py2.5.egg
\sqlalchemy\engine\base.py", line 942, in _handle_dbapi_exception
raise exceptions.DBAPIError.instance(statement, parameters, e,
connection_invalidated=is_disconnect)
InterfaceError: (InterfaceError) Error binding parameter 1 - probably
unsupported type. u'INSERT INTO mg1_model_item ("itemType_id", amount,
quality, owner_id, recipe_id, offered_id, requested_id, proceeds_id,
rawmaterial_id, production_id, tool_id, shop_id) VALUES
(?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)' [0, Decimal("0"), 0, 6, None,
None, None, None, None, None, None, None]
This looks like Elixir/SA is trying to insert the Item object with an
amount column of 0, which is not the desired outcome. (Is Decimal("0")
not supported by SQLite?)
One other complication is that it is possible that SubtractAmount() is
called on an Item which was created during this controller invocation.
Since I think Turbogears uses a ScopedSession for each controller
invocation, I don't explicitly call save() or session.save() on the
newly created items because I thought the ScopedSession took care of
that for me.
I've searched the docs and other messages on this board and can't
figure out what I'm doing wrong. The only example of deleting an
object (and therefore its row(s) in the database) is to either set an
object reference to None, or use Python's "del" statement (which
yields the same error).
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