yes please see the "polymorphic association" example included in the
distribution .
On Jun 21, 2010, at 3:44 PM, Ryan I. wrote:
> How would one go about modeling a relationship where one class can be
> a child of many classes. For example, let's say I have a lot of
> classes like this:
>
> class Cat(Base):
> __tablename__ = 'cats'
> class Dog(Base):
> __tablename__ = 'dogs'
> class Mouse(Base):
> __tablename__ = 'mice'
> class Bird(Base):
> __tablename__ = 'birds'
>
> Now, I want to tag instances of all those classes, but I want to use
> just one class and one table to store the tags. I want to aviod having
> CatTag, DogTag, MouseTag classes. I guess I can store the tags in a
> table like this:
>
> tags_table = Table('tags', metadata,
> Column('id', Integer, primary_key=True),
> Column('type', UnicodeText),
> Column('object_id', Integer,
> Column('name', UnicodeText))
>
> where `type` can be one of 'cat', 'dog', 'mouse', etc, and `object_id`
> is a foreign key to a coresponding table. Is there a way to model this
> with SQLAlchemy's ORM, so that I can simply write:
>
> tag1, tag2 = Tag(type='dog', name='tag1'), Tag(type='dog',
> name='tag2')
> spotty = Dog()
> spotty.tags = [tag1, tag2]
>
> and that SQLAlchemy does the right thing?
>
> Thanks guys...
>
> ~ Ryan I.
>
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