On Aug 21, 2010, at 12:05 PM, simon wrote:
> Hi all,
>
> For a given declaratively mapped class in SA 0.6, how do I
> programmatically find out all other mapped classes forming a many-to-
> one or many-to-many relationship with it? I know I can ask a table
> object for all its foreign keys, but the information whether it forms
> a many-to-one or a many-to-many relationship is not really contained
> in the schema.
Assuming that relationship() has been configured, you'd retrieve the Mapper for
each class:
from sqlalchemy.orm import class_mapper
mapper = class_mapper(someclass)
you can then iterate through its properties looking for what you need, but note
the API of MapperProperty/RelationshipProperty is less stable than that of
primary ORM constructs:
from sqlalchemy.orm.properties import RelationshipProperty
from sqlalchemy.orm.interfaces import MANYTOMANY, MANYTOONE
for prop in mapper.iterate_properties:
if isinstance(prop, RelationshipProperty):
prop.direction in (MANYTOMANY, MANYTOONE) ...
if OTOH your asking for relationship() to be generated automatically, there's
no completely reliable way to tell if an FK is many to one or many to many,
unless you want to make a guess based on the other columns and constrants on
the referencing table.
>
> Thanks, Simon
>
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