Opened 13 years ago
Closed 11 years ago
#16748 closed New feature (wontfix)
Documentation on creating custom querysets
Reported by: | Owned by: | nobody | |
---|---|---|---|
Component: | Documentation | Version: | |
Severity: | Normal | Keywords: | |
Cc: | mike@…, ognajd@… | Triage Stage: | Accepted |
Has patch: | no | Needs documentation: | no |
Needs tests: | no | Patch needs improvement: | no |
Easy pickings: | no | UI/UX: | no |
Description
Currently Django's documentation describes how customize the manager's initial query set (https://docs.djangoproject.com/en/dev/topics/db/managers/#modifying-initial-manager-querysets), but not how to create filters that can be used on an existing query set, at any position in the chain of filters.
Doing so requires subclassing the queryset object. This blog post describes the issue in more detail and proposes a solution:
http://zmsmith.com/2010/04/using-custom-django-querysets/
It would be helpful if there were an officially approved way to subclass querysets or add custom chainable filters, and it was part of the documentation.
Change History (9)
comment:1 by , 13 years ago
Triage Stage: | Unreviewed → Design decision needed |
---|
comment:2 by , 13 years ago
Triage Stage: | Design decision needed → Accepted |
---|---|
Type: | Uncategorized → New feature |
There really ought to be a better way of making a manager and custom queryset all in one step -- it's a common operation. But until then we should document the crufty way.
follow-up: 5 comment:3 by , 12 years ago
How about something like this:
https://github.com/zacharyvoase/django-qmethod
comment:4 by , 12 years ago
Cc: | added |
---|
Note that the __getattr__
definition in the above boilerplate code violates https://docs.djangoproject.com/en/dev/topics/db/managers/#implementation-concerns
Associated discussion on #15062.
comment:5 by , 12 years ago
Replying to anonymous:
How about something like this:
https://github.com/zacharyvoase/django-qmethod
I second this method (or at least its syntax). I haven't tested it yet in my project, but it looks quite elegant. To me, the use of a separate Manager class makes sense when you might reuse that manager for two different models, but for my app, I usually just need one-off managers anyway. Being able to define custom queryset methods inline in the model class in most cases would make my business logic much simpler.
comment:6 by , 12 years ago
Would something like adding queryset class as an optional parameter to models.Manager make the story a bit cleaner?
class CustomManager(models.Manager): def __init__(self, query_set_class=CustomQuerySet): super(CustomManager, self).__init__(query_set_class=query_set_class)
The code change would look like this: https://github.com/jtillman/django/compare/CustomQuerySet
comment:7 by , 11 years ago
Cc: | added |
---|---|
Version: | 1.3 |
comment:9 by , 11 years ago
Resolution: | → wontfix |
---|---|
Status: | new → closed |
It seems like the related ticket has momentum, so it's probably not worth documenting "the crufty way" at this point.
The solution described in the blog post requires five lines of boilerplate code, which is a blocker for recommending it in the official documentation:
Currently, the docs just describe the APIs of
Manager
andQuerySet
.I don't know if there's a general solution to this problem, if we want to develop one in Django, or just let each developer figure out what's most appropriate in his/her situation.