Question

So I have a query…

qry = Query(models.UserList).filter(...)

models.UserList contains a mixin method that will return a count of a related table

So what I would like to do is something like …

qry = qry.order_by(models.UserList.contactCount)

However this produces invalid sql of course.

So how can I do something like

qry.add_column((this.contactCount).label("contactCount"))

this.contactCount is just bad psuedocode, but hopefully you get the point.

I’ve been looking at how to do this for a while, but sqlalchemy doc isnt the easiest thing to find stuff in.

any help appreciated

Answer 1

You can use either a column_property or a hybrid_property for that. For example:

class UserList(Base):
    ...
    contactCount = column_property(
        select(
            [func.count()],
            contact_id == Contact.id,
        ).label('contactCount'),
        deferred=True,
    )