#20932: Issues with model Manager and inheritance.
-------------------------------------+-------------------------------------
Reporter: loic84 | Owner: nobody
Type: Bug | Status: new
Component: Database layer | Version: master
(models, ORM) |
Severity: Normal | Resolution:
Keywords: | Triage Stage: Accepted
Has patch: 1 | Needs documentation: 0
Needs tests: 1 | Patch needs improvement: 1
Easy pickings: 0 | UI/UX: 0
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Changes (by mjtamlyn):
* cc: mjtamlyn (added)
Comment:
I think that backwards incompat is acceptable, and pretty natural. The end
result here becomes easy to explain:
- Resolve managers explicitly defined on all models you inherit from
(irrespective of their abstract or concrete nature) using normal MRO
- If there are no managers explicitly defined, create `objects =
models.Manager()` as every model must have a manager.
The guiding point being the implicit creation is a last resort.
Because the existing behaviour is strange and incorrectly documented,
there's no harm in rewriting it to make it logical. It should be easy to
make loud warnings that `MessyBachelorParty.objects` is not defined as
`MessyBachelorParty.events` is.
----
The other alternative approach, which I have to say I quite like but would
be more far reaching, is to effectively define `objects` on `Model` and
let normal MRO do the rest (subject to model binding). This would mean
every model has a manager called `objects`, which is either the default
manager or a defined custom manager. We scrap `_default_manager` and just
use objects as the default. This would be a much bigger backwards
incompatibility, but in my experience whenever I do define a custom
manager, I either call it `objects`, or call it something else and
redefine `objects`. I find the disappearing nature of `objects` somewhat
strange and magical. Such a change would need to be discussed on the
mailing list, what I'm curious about is whether anyone actually has a
concrete need for `objects` to disappear.
--
Ticket URL: <https://code.djangoproject.com/ticket/20932#comment:14>
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