> we have the "wrapper" thing, its the associationproxy. docs are
> here: http://www.sqlalchemy.org/docs/04/plugins.html#plugins_associationproxy
> .
>
> In this case you'd probably map a class to the user_articles_table and
> use associationproxy to create user.articles against "article id".
Hi again, thanks for your pointers. I'm still having trouble,
unfortunately.
I now have the following schema set up:
------
users_table = Table('tg_user', metadata,
Column('user_id', Integer, primary_key=True),
...)
user_articles_table = Table('user_article', metadata,
Column('user_id', Integer, ForeignKey('tg_user.user_id')),
Column('article_hash', String(32)),
)
def _create_ua_by_article(article):
""" A creator function. """
return UserArticle(article_hash=article)
class User(object):
...
saved_articles = association_proxy('user_articles',
'article_hash', creator=_create_ua_by_article)
class UserArticle(object):
""" Joining relationship between Users and articles (articles
stored elsewhere) """
def __init__(self, user=None, article_hash=None):
self.user = user
self.article_hash = article_hash
mapper(User, users_table, properties={
'user_articles': relation(UserArticle),
})
mapper(UserArticle, user_articles_table, properties={
'user': relation(User),
})
------
Unfortunately this schema won't generate the tables without
complaining about no primary key on user_articles, so I made both
columns on UserArticle a primary_key which seemed to work okay.
So, adding articles to the user.saved_articles list seems to work, and
the database reflects this, however, trying to remove an article
raises an exception: "AssertionError: Dependency rule tried to blank-
out primary key column 'user_article.user_id' on instance
'[EMAIL PROTECTED]'"
I've demonstrated this in the following session. If someone could
point out where I'm going wrong, I'd be most grateful :)
------
>>> session.begin()
<sqlalchemy.orm.session.SessionTransaction object at 0x1580550>
>>> user = session.query(User).first()
>>> user.user_id
1
>>> user.saved_articles
['5e4dda932fce6b9a68f370406526cb10',
'bc21f67412bca994acd1af8b1dd78942']
>>> user.saved_articles.append('f3529aac5eda60741e9e9dab7bea905d')
>>> session.commit()
>>> user.saved_articles
['5e4dda932fce6b9a68f370406526cb10',
'bc21f67412bca994acd1af8b1dd78942',
'f3529aac5eda60741e9e9dab7bea905d']
>>> session.begin()
<sqlalchemy.orm.session.SessionTransaction object at 0x15e1890>
>>> user.saved_articles.remove('f3529aac5eda60741e9e9dab7bea905d')
>>> session.commit()
Traceback (most recent call last):
File "<console>", line 1, in ?
File "/usr/lib/python2.4/site-packages/SQLAlchemy-0.4.6-py2.4.egg/
sqlalchemy/orm/scoping.py", line 98, in do
return getattr(self.registry(), name)(*args, **kwargs)
File "/usr/lib/python2.4/site-packages/SQLAlchemy-0.4.6-py2.4.egg/
sqlalchemy/orm/session.py", line 554, in commit
self.transaction.commit()
File "/usr/lib/python2.4/site-packages/SQLAlchemy-0.4.6-py2.4.egg/
sqlalchemy/orm/session.py", line 259, in commit
self._prepare_impl()
File "/usr/lib/python2.4/site-packages/SQLAlchemy-0.4.6-py2.4.egg/
sqlalchemy/orm/session.py", line 243, in _prepare_impl
self.session.flush()
File "/usr/lib/python2.4/site-packages/SQLAlchemy-0.4.6-py2.4.egg/
sqlalchemy/orm/session.py", line 786, in flush
self.uow.flush(self, objects)
File "/usr/lib/python2.4/site-packages/SQLAlchemy-0.4.6-py2.4.egg/
sqlalchemy/orm/unitofwork.py", line 233, in flush
flush_context.execute()
File "/usr/lib/python2.4/site-packages/SQLAlchemy-0.4.6-py2.4.egg/
sqlalchemy/orm/unitofwork.py", line 445, in execute
UOWExecutor().execute(self, tasks)
File "/usr/lib/python2.4/site-packages/SQLAlchemy-0.4.6-py2.4.egg/
sqlalchemy/orm/unitofwork.py", line 930, in execute
self.execute_save_steps(trans, task)
File "/usr/lib/python2.4/site-packages/SQLAlchemy-0.4.6-py2.4.egg/
sqlalchemy/orm/unitofwork.py", line 948, in execute_save_steps
self.execute_dependencies(trans, task, False)
File "/usr/lib/python2.4/site-packages/SQLAlchemy-0.4.6-py2.4.egg/
sqlalchemy/orm/unitofwork.py", line 959, in execute_dependencies
self.execute_dependency(trans, dep, False)
File "/usr/lib/python2.4/site-packages/SQLAlchemy-0.4.6-py2.4.egg/
sqlalchemy/orm/unitofwork.py", line 942, in execute_dependency
dep.execute(trans, isdelete)
File "/usr/lib/python2.4/site-packages/SQLAlchemy-0.4.6-py2.4.egg/
sqlalchemy/orm/unitofwork.py", line 895, in execute
self.processor.process_dependencies(self.targettask, [elem.state
for elem in self.targettask.polymorphic_tosave_elements if elem.state
is not None], trans, delete=False)
File "/usr/lib/python2.4/site-packages/SQLAlchemy-0.4.6-py2.4.egg/
sqlalchemy/orm/dependency.py", line 193, in process_dependencies
self._synchronize(state, child, None, True, uowcommit)
File "/usr/lib/python2.4/site-packages/SQLAlchemy-0.4.6-py2.4.egg/
sqlalchemy/orm/dependency.py", line 249, in _synchronize
sync.clear(dest, self.mapper, self.prop.synchronize_pairs)
File "/usr/lib/python2.4/site-packages/SQLAlchemy-0.4.6-py2.4.egg/
sqlalchemy/orm/sync.py", line 32, in clear
raise exceptions.AssertionError("Dependency rule tried to blank-
out primary key column '%s' on instance '%s'" % (r,
mapperutil.state_str(dest)))
AssertionError: Dependency rule tried to blank-out primary key column
'user_article.user_id' on instance '[EMAIL PROTECTED]'
------
Thanks,
Nick
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