On Thursday, October 12, 2017 at 5:47:53 PM UTC+2, Mike Bayer wrote: > > > It sounds like you are getting back inconsistent SQL for the same > query based on some external context that is not being considered as > part of the cache key. This would indicate that you are probably > modifying the select() object *in place* inside your before_execute > hook. If your before_execute() hook returns a *new* select() > object, it would not pollute the cache with your late-modified value > against the cache keys. > > That is, it's the difference between calling > select.append_whereclause() and select.where(). The > before_execute() hook would need to be set up with retval=True and > return the new statement and parameters. > > Bingo! Looking at the code it has append_from() and append_whereclause() calls, so it's probably modifying in place. Sigh. That probably means this is going to break the caching in even more spectacular ways which we haven't yet spotted. The action of the hook is indeed dependant on something that is not part of the query, namely the "perms" field which only exists in our own CheckedQuery class.
The concept of the hook is pretty simple. It looks through the query for which tables it uses and if it finds a table marked as "special" it adds a filter and possibly some joins. I'm fairly sure this could be done safely using the Visitor pattern, in practice it's one big ball of spaghetti no-one wants to touch. Essentially it looks for a table and replaces it with a subquery, but it works by looping/recursing through the fields of the query itself. Ugh. I think we're going to have to drop the idea of the hook in the long term, and at least short-circuit it for baked-queries, putting the query rewriting in our wrapper, then it can be cached like the rest. Especially since in 1.2 lazy loading is going to trigger this (though probably disable lazy loading in most places). Caching the query rewriting isn't a bad plan either. But it looks like our query rewriting is more of a liability than I thought. Thanks for the help! Have a nice day, -- Martijn -- SQLAlchemy - The Python SQL Toolkit and Object Relational Mapper http://www.sqlalchemy.org/ To post example code, please provide an MCVE: Minimal, Complete, and Verifiable Example. See http://stackoverflow.com/help/mcve for a full description. --- You received this message because you are subscribed to the Google Groups "sqlalchemy" group. To unsubscribe from this group and stop receiving emails from it, send an email to sqlalchemy+unsubscr...@googlegroups.com. To post to this group, send email to sqlalchemy@googlegroups.com. Visit this group at https://groups.google.com/group/sqlalchemy. For more options, visit https://groups.google.com/d/optout.
