Hi,
I just noticed that User.groups relationship is not needed at all (it was a
relict of previous setup before System column was added).
So the problem is completely gone.
---
I already use *AssociationProxy* pattern in order to have relations like
*User.A_groups,
User.B_group**s, USer.C_groups.*
However I figured out other issue that '*creator*' callback to
*AssociationProxy* does not pass the parent object to it, which is weird.
See example:
user = ScopedSession.query(User).get('fred')
user.A_groups = [ Group('admins') ]
It should create also intermediary instance of User2Group. It does, but
user attribute of intermediary object is null.
So I created *AssociationFactory* as the following:
class AssociationFactory(AssociationProxy):
def __init__(self, *args, **kwargs):
self.creator_factory = kwargs.pop('creator_factory')
super(AssociationFactory, self).__init__(*args, **kwargs)
def __get__(self, obj, class_):
if obj:
self.creator = self.creator_factory(weakref.ref(obj))
return super(AssociationFactory, self).__get__(obj, class_)
for system in ('A', 'B', 'C'):
def creator_factory(user_ref):
def creator(group):
user = user_ref()
if user is None:
raise TypeError('Stale object reference')
return User2Group(user=user, group=group, system=system)
return creator
setattr(User, system + '_groups',
AssociationFactory(system+'_users2groups', 'group',
creator_factory=creator_factory)
Then all works nicely. Do you see the point?
cheers!
Dne čtvrtek 5. března 2015 11:58:50 UTC+1 Simon King napsal(a):
>
> Glad you've figured it out. This is touched on briefly in the docs, in
> the note at the bottom of:
>
>
> http://docs.sqlalchemy.org/en/rel_0_9/orm/basic_relationships.html#association-object
>
>
> As an alternative to making User.groups a relationship, you could also
> consider using the Association Proxy extension:
>
>
> http://docs.sqlalchemy.org/en/rel_0_9/orm/extensions/associationproxy.html#simplifying-association-objects
>
>
> Hope that helps,
>
> Simon
>
>
> On Thu, Mar 5, 2015 at 10:43 AM, Pavel S <pa...@schon.cz <javascript:>>
> wrote:
> > Hi,
> > Adding viewonly=True on User.groups relationship solved the issue.
> > cheers!
> >
> > Dne čtvrtek 5. března 2015 11:26:58 UTC+1 Pavel S napsal(a):
> >>
> >> Hello,
> >>
> >> I have relation User-User2Group-Group with additional attribute System
> on
> >> User2Group table.
> >> The System is part of primary key, which means 'user can me member of
> >> group via multiple systems'.
> >>
> >> class User(Base):
> >> __tablename__ = 'User'
> >>
> >> name = Column('Name', Unicode(256), primary_key=True)
> >>
> >> class Group(Base):
> >> __tablename__ = 'Group'
> >>
> >> name = Column('Name', Unicode(256), primary_key=True)
> >>
> >> class User2Group(Base):
> >> __tablename__ = 'User2Group'
> >>
> >> userName = Column('UserName', Unicode(256), ForeignKey(User.name),
> >> primary_key=True)
> >> groupName = Column('GroupName', Unicode(256),
> ForeignKey(Group.name),
> >> primary_key=True)
> >> systemName = Column('SystemName', Enum('A', 'B', 'C'),
> >> primary_key=True)
> >>
> >> User.groups = relationship(Group, secondary=User2Group.__table__)
> >>
> >>
> >> Table User2Group looks like following
> >>
> >> UserName | GroupName | SystemName
> >> ---------------------------------
> >> fred | admins | A
> >> fred | admins | B
> >> fred | admins | C
> >>
> >>
> >> However when trying to delete user 'fred' wich is assinged to group
> >> 'admins' via multiple systems A, B, C.
> >>
> >> I'm getting error: DELETE statement on table 'User2Group' expected to
> >> delete 1 row(s); Only 3 were matched.
> >>
> >> Did I misconfigured something?
> >>
> >> Thanks
> >>
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