Hi,
Recently we've been looking into the baked query feature as a method of
speeding up query compilation. We also use a before_execute hook to modify
the query before execution to handle permission related stuff. One thing
that turned up was that when using a baked query that it cached the final
string version.
What this means is that the baked query framework caches the results of the
before_execute hook meaning that queries occasionally produce the wrong
output in situations where the before_execute hook would do something
different. I'm not clear if this is a bug or a "you break it you get to
keep both pieces".
We worked around this (yes, before_execute hooks are evil) but this became
more urgent when an old product accidentally got SQLAlchemy 1.2.0b where
baked queries are used for lazy loading, which caused all sorts of funky
errors. Whoops!
I'm wondering if there is a way of at least detecting this? Such that if a
before_execute hook changes a query that the result is automatically not
cached. That would at least prevent things from breaking unexpectedly. But
long term, caching the compilation is really nice and so we'd like to be
able to keep that feature. Our hook is predictable such that with the same
input query and a parameters which is stored in the Query object you always
get the same result. So it would in theory be possible to work with the
baked query framework, but I'm totally not clear how that would work.
Any ideas?
As an aside, we worked around a few things by creating a WrappedBakedQuery
class, which allowed us to do thing like:
baked_query += lambda q: q.filter(Table.col == bind_param('foo'))
baked_query.set_param('foo', 1)
Which worked better in our setup.
Have a nice day,
--
Maritjn
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