On Apr 25, 2011, at 9:10 PM, Andrey Petrov wrote:
> One more thought:
>
> Is there a sane way to hide a schema object within another schema object?
>
> Specifically, I want to make a factory method (or maybe a class decorator)
> which generates these Tag schemas onto specific tables. Something along the
> lines of:
>
> @Taggable
> class User(BaseModel)
> __tablename__ = "user"
>
> The Taggable class decorator would generate another table called "tag_user"
> and attach the appropriate relationship attributes to the User class. I'm
> thinking it'll also attach the anonymous Tag declarative class to the User
> class as User.TagClass or somesuch.
>
> Is this reasonable? Is there a better way to do this than monkey-patching the
> User class in the Taggable decorator?
>
> One fantasy I had was if you could do...
>
> class TaggableMixin(object):
> @declared_attr
> def TaggableClass(cls):
> class Tag(BaseModel):
> __tablename__ = "tag_%s" % cls.__tablename__
> # ... schema here
>
> class User(BaseModel, TaggableMixin):
> # ...
>
> Perhaps I should try it but I don't imagine this will work.
you should create tables inside of @declared_attr. Usually I'm using straight
Table in there but declared class should work too (though you might get a
warning about the same class created twice, unless you do some kind of
uniqifying, it probably would be nice to fix declarative to not call any
@declared_attr twice). For the "already have this table in this metadata"
issue use the table argument "keep_existing=True".
Otherwise, I do this exact pattern you have above except explicitly:
class UserTag(TagBase, Base):
__tablename__ = 'user_tag'
class User(Taggable, Base):
tag_cls = UserTag
TagBase and Taggable do the rest of the work.
*maybe* this works too:
class User(Taggable, Base):
class tag_cls(TagBase, Base):
__tablename__ = 'user_tag'
You could also use an event like "instrument_class" or "mapper_configured" ,
associated with mapper() and would look for Taggable subclasses.
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