On Jun 7, 2012, at 10:41 PM, Danosaure wrote:
> I'm confused at how to use orm.aliased(). I'm using declarative base.
>
> I have a class defined from
>
> Base.metadata.reflect(engine)
> class Summary(Base):
> __table__ = Base.metadata.tables['summary']
>
>
> Now, I want to use that class in a self join
>
> class JoinSummary(Base):
> s1 = orm.aliased(Summary, name='summary1')
> s2 = orm.aliased(Summary, name='summary2')
>
> __select__ = sqlalchemy.select([...],
> from_obj=s1.__table__.outerjoin(s2.__table__, s1.attr1 ==
> s2.attr2)).where(...)
> __table__ = __select__.alias('my_join_summary')
>
>
> But as soon as I do Session.query(Join.Summary.__select__), I get the
> following error:
>
> sqlalchemy.exc.ProgrammingError: (ProgrammingError) (1066, "Not unique
> table/alias: 'summary'", None)
>
> I must not been using the aliased() as it should.
>
> Your help will be much appreciated.
>
> Thanks.
>
>
> I am not sure how to do what I want: create a view class that I can use later
> in Session.query().
How come you're making some kind of mapping to this new __select__, but then
when you use query() you're not making this query towards the JoinSummary class
? the example seems a little torn as to what it wants to do.
The error means that the generated SQL contains a FROM leading to the name
"summary" more than once.
Basically the use case of deriving __table__ from AliasedClass, which would
then be expected to be the "aliased" table, was never anticipated -
aliased(orm_object) was only meant to produce a new class that itself was the
"alias" object that can be used in a query. So __table__ is still the
"summary" table here. It might not be a bad idea to change this. (though
not mid-0.7, would be another 0.8 thing).
But anyway yeah that's not really how I anticipated aliased(orm_object) being
used. If you want to work with SQL Expression level aliases I'd build that
directly:
a1 = Summary.__table__.alias('summary1')
a2 = Summary.__table__.alias('summary2')
my_select = select(..)... etc
result = session.execute(my_select)
>
>
>
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