Kent wrote: > The limit() function behaves in a way that is possibly unexpected: > > If you ask sqlalchemy to query "limit(3)" where a join is involved, > for example, and 2 of the "top-3" are actually the same primary key, > sqlalchemy gets the 3 results, throws out the duplicate and your query > size ends up as 2. This gives the impression there are no more > matches because you asked for 3 and got only 2, when in fact you may > have hundreds of possible rows. > > Right off, I can't think of an elegant solution to this behavior. > Certainly sqlalchemy could *detect* the problem after the fact and re- > request a greater limit, but that is ugly hackish and results in > multiple trips to the database, sqla wouldn't know how many to re- > request, etc... > > sqlalchemy could request "DISTINCT" results, but I'm not sure how > easily that could be implemented or what it may break. > > Interested if anyone has an elegant solution?
this is a natural effect of placing LIMIT on a query with a join. To limit the "inner" results only, use query.limit(N).from_self().join(...) which will apply the LIMIT to a subquery. SQLAlchemy's "eager loading" feature also does this subquery effect as needed. from_self() was added so that users could have access to this functionality in a more generic way. the Query remains explicit about join() and the fact that you're working with SQL - so from_self() is a necessary explicit step too. > -- > You received this message because you are subscribed to the Google Groups > "sqlalchemy" group. > To post to this group, send email to sqlalch...@googlegroups.com. > To unsubscribe from this group, send email to > sqlalchemy+unsubscr...@googlegroups.com. > For more options, visit this group at > http://groups.google.com/group/sqlalchemy?hl=en. > > > -- You received this message because you are subscribed to the Google Groups "sqlalchemy" group. To post to this group, send email to sqlalch...@googlegroups.com. To unsubscribe from this group, send email to sqlalchemy+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en.
