Sorry for the double thread. I was waiting for it to show up for
hours. Please remove one of them. Thanks
On Nov 9, 4:44 pm, Torsten Engelbrecht
<torsten.engelbre...@googlemail.com> wrote:
> Hi,
>
> I need to use dynamic table names in a project (though for the same
> object). Now I got the following problem:
> - I fetch data from an RSS feed to fill my database. Its an RSS feed
> with many pages, each page has around 100 items
> - I fetch the first page and create a table + mapper for a dynamic id
> (called "my_id" below)
> - then I do session.add and session.commit for each item in the feed,
> everything ok so far
> - after I fetch the second page ("my_id" is the same), I attempt to
> recreate table and mapper (see code below) or simply readd them if
> they already exist, that seems working as well
> - I do the same for each item in the feed as the first time, but this
> time it raise the following exception:
> "sqlalchemy.orm.exc.FlushError: Instance <MyModel at 0x1bc1590> has a
> NULL identity key. Check if this flush is occuring at an
> inappropriate time, such as during a load operation."
>
> Here my data model (simplified) and the code to simply save a new item
> from the feed:
>
> ===
> import sqlalchemy
> from sqlalchemy import import orm
>
> mymetadata = sqlalchemy.MetaData()
>
> class MyModel(object):
> def __init__(self, **kwargs):
> title = kwargs.get('title')
> body = kwargs.get('body')
>
> class MyModelTable(object):
> def __init__(self, my_id):
> metadata = mymetadata
> table_name = 'mymodel_%s' % my_id
> self.table = sqlalchemy.Table(table_name, metadata,
> sqlalchemy.Column('id', sqlalchemy.Integer,
> primary_key=True),
> sqlalchemy.Column('title', sqlalchemy.String(255),
> index=True),
> sqlalchemy.Column('body', sqlalchemy.Text),
> useexisiting=True)
> self.table.create(get_engine(), checkfirst=True) #get_engine()
> is helper function to retrieve the engine (not listed here)
> orm.mapper(MyModel, self.table)
>
> def save_items(my_id, items): #assuming items is already parsed and
> saved in a list
> model_table = MyModelTable(my_id)
> session = orm.sessionmaker(bind=get_engine(), autocommit=False,
> autoflush=True)
> for item in items:
> item_data = dict(title=item['title'],
> body=item['description'])
> new_model_instance = MyModel(**item_data)
> session.add(new_model_instance)
> session.commit()
> session.close()
> orm.clear_mappers() #to avoid the exception when mapping the same
> object to anoher ot the same table
> ===
>
> Here is the whole traceback after the commit:
> ===
> File "/usr/local/lib/python2.6/dist-packages/SQLAlchemy-0.6.5-
> py2.6.egg/sqlalchemy/orm/session.py", line 623, in commit
> self.transaction.commit()
> File "/usr/local/lib/python2.6/dist-packages/SQLAlchemy-0.6.5-
> py2.6.egg/sqlalchemy/orm/session.py", line 385, in commit
> self._prepare_impl()
> File "/usr/local/lib/python2.6/dist-packages/SQLAlchemy-0.6.5-
> py2.6.egg/sqlalchemy/orm/session.py", line 369, in _prepare_impl
> self.session.flush()
> File "/usr/local/lib/python2.6/dist-packages/SQLAlchemy-0.6.5-
> py2.6.egg/sqlalchemy/orm/session.py", line 1397, in flush
> self._flush(objects)
> File "/usr/local/lib/python2.6/dist-packages/SQLAlchemy-0.6.5-
> py2.6.egg/sqlalchemy/orm/session.py", line 1487, in _flush
> flush_context.finalize_flush_changes()
> File "/usr/local/lib/python2.6/dist-packages/SQLAlchemy-0.6.5-
> py2.6.egg/sqlalchemy/orm/unitofwork.py", line 320, in
> finalize_flush_changes
> self.session._register_newly_persistent(state)
> File "/usr/local/lib/python2.6/dist-packages/SQLAlchemy-0.6.5-
> py2.6.egg/sqlalchemy/orm/session.py", line 1056, in
> _register_newly_persistent
> 'operation.' % mapperutil.state_str(state))
> sqlalchemy.orm.exc.FlushError: Instance <MyModel at 0x1bc1590> has a
> NULL identity key. Check if this flush is occuring at an
> inappropriate time, such as during a load operation.
> ===
>
> save_items() is called each time a new page is fetched (either for the
> same "my_id") or another one.
> This FlushError only happens when I have more than one page for the
> same "my_id" and they are saved one after another. I also never
> happens for the first page, neither for different "my_id"'s when
> staying with one page.
> According to the release notes of SQLAlchemy 0.6.5 this exception
> raises when
> ===
> "Added an assertion during flush which ensures
> that no NULL-holding identity keys were generated
> on "newly persistent" objects.
> This can occur when user defined code inadvertently
> triggers flushes on not-fully-loaded objects. "
> ===
> Though I don't see why it happens in my example. I appreaciate any
> help. Thanks
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