Michael Bayer wrote:
1 - duplicate code on each class (there are a lot of classes!)
seems like a function you'd only need once, on a base class or similar.
OK, so the problems I had before with base classes were because I tried
to have columns on my base classes?
2 - feels like something that SA might provide itself
does SQLA assume that all mapped objects have a field called "name" and
are retrieved using a filter on a single column ?
Well, I was thinking a little more abstractly than that ;-)
The "general" purpose version of such a
function would require writing out the whole query in a callable anyway
so it doesn't make things any simpler than just using python.
I suppose, I guess I was hoping for something that took a
query-that-could-only-return-one-object and returned either that object
or a new one of the right type. Of course, I can see how that would be
an unreasonable request ;-)
find_or_create() is also not very performant in the case where you're
better off loading a whole set of rows first, so not a default the core
needs to be recommending.
True, but if you were using it, you'd likely only be wanting one row at
a time...
OK, so why not put it in a base class? 'cos Declarative doesn't like
base classes that don't map to a table, and writing a metaclass for
this feels heinous...
declarative_base accepts an existing class, which you can apply whatever
lookups and such before turning it into a declarative base.
I'm not sure I ever found an answer to my related question: is it okay
to have a load of declarative_base classes floating around? I guess it
shouldn't matter provided I get them all using the same metadata object.
How would I do that?
Writing a
metaclass is also a good way go, for the purposes of extending
declarative to do what you want, not provide the actual find_or_create,
which you still can put on a subclass.
Application developers should never be writing metaclasses! ;-)
(framework developers fair enough, but you guys have bigger and more
careful brains...)
Chris
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