Seth wrote:
>
> Michael,
>
> Thank you for your quick reply, however I must apologize as I'm a bit
> of a SQLAlchemy newbie.
>
> In the app I'm using the tables are setup using DeclarativeBase, so
> the mapper() function is confusing me with its need for a class to be
> defined as well as a table_name = Table(); and then using table_name
> in the mapper call. Is it possible to use mapper() in a
> DeclarativeBase setup where your columns are defined inside the class?
>
> For reference, here's the Post class:
>
> class Post(DeclarativeBase):
> __tablename__ = 'posts'
>
> def __init__(self, id, user_id, body):
> self.id = id
> self.user_id = user_id
> self.body = body
>
> id = Column(Integer, autoincrement=True, primary_key=True)
> user_id = Column(Integer, ForeignKey('users.id'), nullable=False)
> body = Column(UnicodeText, nullable=False)
>
> user = relation('User', order_by='Post.id', backref='posts')
> comments = relation('Comments')
>
>
> How would you apply your suggested mapper() call to this type of
> setup? Or do I need to switch things to the "more traditional"
> approach?
there's no restriction when using declarative. you'd still use
`column_property()` and you can construct SQL expressions using the Column
objects you've just created, i.e.
comment_count =
column_property(select([func.count(Comment.id)]).where(Comment.post_id==id))
note the usage of "id" which is just the "id" Column object that exists
within the scope of the `User` class declaration.
If its really problematic to have `Comment.id` and `Comment.post_id`
available at that point, you can tack on the property after both classes
are created, which behind the scenes results in an `add_property()` call:
Post.comment_count =
column_property(select([...]).where(Comment.post_id==Post.id))
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