#20625: Custom Chainable QuerySets
-------------------------------------+-------------------------------------
Reporter: danols | Owner: loic84
Type: New feature | Status: assigned
Component: Database layer | Version: master
(models, ORM) | Resolution:
Severity: Normal | Triage Stage: Accepted
Keywords: QuerySet, | Needs documentation: 1
models.Manager, chainable | Patch needs improvement: 1
Has patch: 1 | UI/UX: 0
Needs tests: 1 |
Easy pickings: 0 |
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Comment (by akaariai):
Sorry for the Django super() requirement confusion.
While writing my previous post I got an idea. I did some quick testing and
it seems the idea needs to be presented. There are two key things in the
idea:
- Managers are created by CustomQuerySet.manager_cls() method - this is
a factory constructing a new manager class.
- The new manager class has dynamically created proxy methods for those
methods in the CustomQuerySet that should be present in the manager.
So, you could do something like this:
{{{
class MyQuerySet(models.QuerySet):
def bar(self):
return ...
bar.manager = True
class MyModel(Model):
objects = MyQuerySet.as_manager()
}}}
Now, MyModel.objects is a custom Manager subclass which has a proxy method
for bar(). And it really *has the method*, so super() works correctly.
The API might not be optimal, but the idea that proxy methods are
automatically created on dynamically created Manager classes should be
considered carefully. In my opinion it offers better semantics than the
`__getattr__` based approach.
I wrote a very quick proof-of-concept patch. It is available from:
https://github.com/akaariai/django/tree/manager_factory. The only
interesting part of the patch is the method at
https://github.com/akaariai/django/commit/283af213d1873cefd642b6d9aeb97f285ef227c4#L2R44
--
Ticket URL: <https://code.djangoproject.com/ticket/20625#comment:20>
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