On May 10, 2007, at 12:05 PM, Chris Perkins wrote:
> if 0:
> # This works fine:
> pjoin = (T1_select.c.id==T2_select.c.parent_id) &
> (T1_select.c.ver==T2_select.c.parent_ver)
> fks = [T1_select.c.id, T1_select.c.ver]
>
> else:
> # But this does not:
> pjoin = (T1.c.id==T2.c.parent_id) & (T1.c.ver==T2.c.parent_ver)
> fks = [T1.c.id, T1.c.ver]
>
> m1.add_property('my_twos', relation(Two, primaryjoin=pjoin,
> foreign_keys=fks))
>
the second version is not going to work because you are expressing
the joins and foreign keys in terms of the underlying tables, not the
relations to which the mappers are bound (i.e. T1_select,
T2_select). so the mapper cant do anything with that (more
specifically, it decides not to try and interpolate the columns into
the corresponding columns on the selectable...since that doesnt
really work for relationships between selectables that both include
the same underlying tables).
it works when you have the foreign keys directly on the tables
because the select()s you create propigate the constraints from their
underlying selected tables into the appropriate constraints for that
select object (and also know how to join each other). i.e.:
>>> [(f.column, f.parent) for f in T2_select.foreign_keys]
[('T1.id', 'T2_select.parent_id'), ('T1.ver', 'T2_select.parent_ver')]
>>> T1_select.join(T2_select).onclause
"T1_select".id = "T2_select".parent_id AND "T1_select".ver =
"T2_select".parent_ver
so that produces the same effective arguments you have in the first
version.
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