[Sqlalchemy-tickets] Issue #3225: query heuristic extension (zzzeek/sqlalchemy)

[Mike B. <iss...@bi...>]

New issue 3225: query heuristic extension
https://bitbucket.org/zzzeek/sqlalchemy/issue/3225/query-heuristic-extension

Mike Bayer:

given issues like #3223 and the openstack issues with model_query(), here's a sketch of an idea:

```
#!python




@event.listens_for(EventedQuery, "whereclause", retval=True)
def append_whereclause(existing_query, new_query, clause):
    if clause.selects_against(MyOtherClass):
        for entity, expression in new_query.selects_against(MyClass):
            new_query = new_query.join(MyOtherClass, MyClass.myother)
    return new_query

@event.listens_for(EventedQuery, "selects_from_entity", retval=True)
def append_order_by(existing_query, new_query, entity, expression):
    for entity, expression in new_query.selects_against(MyClass):
        new_query = new_query.order_by(entity.whatever)
    return new_query

@event.listens_for(EventedQuery, "before_compile", retval=True)
def append_order_by(new_query):
    if new_query.selects_against(MyClass):
        for entity, expression in new_query.selects_against(MyClass):
            new_query = new_query.order_by(entity.whatever)
    return query

```