On Nov 11, 2010, at 7:50 PM, Sergey V. wrote:
>
>> relationship() expects a class or a mapper instance, not a string. I
>> got this error:
>>
>> ArgumentError: relationship 'available_deals' expects a class or a
>> mapper argument (received: <type 'str'>)
>
> Hmm... I'm not sure what I'm doing wrong but passing strings to
> relation() definitely works for me:
The difference here is that usage of declarative adds an extra handler to
relationship() calls, such that strings passed for most of its arguments are
converted to callables which are later evaluated when the mapper structure is
initialized.
You should be able to use relationship() in a "deferred argument " style
without declarative by using lambdas, i.e.:
relationship(lambda: MyClass, primaryjoin=lambda:MyClass.foo==OtherClass.bar)
But generally usage of mapper() wasn't intended to provide any "tricks" around
import issues. You can always use mapper.add_property(...) to attach things as
needed, and class_mapper(Class) to call up any mapper anywhere.
>
>
> class Host(Base):
>
> __tablename__ = 'hosts'
> id = sa.Column(sa.Integer, primary_key = True)
> ...
> datacentre_id = sa.Column(sa.Integer,
> sa.ForeignKey('datacentres.id'))
> datacentre = sa.orm.relation('Datacentre', backref='hosts')
>
> Can it be because I'm using declarative? In my case I don't even need
> to import Datacentre class before I declare Host class.
>
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