[sqlalchemy] Re: scalar association_proxy
Maybe you can squelch the exception by using a synonym with the descriptor argument to map to a fake property. Oooh, I had not come across this construct before - looks as if it might do exactly what I want. I might even be able to make a decorator that wraps this all up nicely. Thank you very much; I shall let you know how I get on! -- You received this message because you are subscribed to the Google Groups sqlalchemy group. To post to this group, send email to sqlalchemy@googlegroups.com. To unsubscribe from this group, send email to sqlalchemy+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en.
[sqlalchemy] scalar association_proxy
Hi Folks, I have been scratching my head over this one all day, so any advice would be greatly appreciated! I have a pretty simple join table setup like this: foo foo_bar bar --- id id_foo (unique) id id_bar more_stuff It looks like a many-to-many relationship, but it's not, since id_foo is unique in the join table. - There can be any number of 'foo' for each 'bar' - Each 'foo' has exactly one or zero 'bar' I have set up the required declarative stuff, and an association proxy in 'foo' to get to 'bar' in one nice step. Since there can only ever be one (or zero - and this is my problem) I have set it to be a scalar. It all works great, except that if I try and look at the value of the assoication proxy in a 'foo' row without a corresponding 'foo_bar', then I get AttributeError. It is clearly looking for a 'bar' in a 'foo_bar' that is a None (since there is no entry), so is understandable; but in my case not desirable. What I would like to do is to get a 'bar' if one exists, else return a 'None'. Is the only way to do this to write my own wrapper property that does a try/catch? And if I do this, will the property stop being nice and magical (you know, filterable and comparable etc..) I am quite a newcomer to SQLAlchemy so go easy on me! All the best, Philip -- You received this message because you are subscribed to the Google Groups sqlalchemy group. To post to this group, send email to sqlalchemy@googlegroups.com. To unsubscribe from this group, send email to sqlalchemy+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en.
[sqlalchemy] Re: scalar association_proxy
Hi ho,
Thanks for the swift reply!
Did you use uselist=False on foo.bar and the associationproxy? It would nice
if you could show some
code.http://www.sqlalchemy.org/docs/orm/extensions/associationproxy.html?h...
Yes I did. The code is more complicated as it has a bunch of other
stuff in it, but here's a condensation:
class Foo(Base):
id = Column(Integer, primary_key = True)
foo_bar_join = relationship(FooBar, primaryjoin = (id ==
FooBar.id_foo), uselist = False)
bar = association_proxy('foo_bar_join', 'bar', creator = lambda x:
FooBar(bar = x) )
class Bar(Base):
id = Column(Integer, primary_key = True)
class FooBar(Base):
id_foo = Column(Integer, ForeignKey('foo.id'), primary_key = True)
id_bar = Column(Integer, ForeignKey('bar.id'), primary_key = True)
bar = relationship(Bar, primaryjoin = (id_bar == Bar.id))
other_stuff = Column(Integer)
The problem comes if you try to fetch 'bar' from an instance of 'Foo'
for which there is no entry in the foo_bar join table.
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