Opened 8 years ago

Closed 6 months ago

#10532 closed Bug (fixed)

An overridden get method on a custom manager passed to get_object_or_404 will not be called.

Reported by: anonymous Owned by: Claude Paroz <claude@…>
Component: Database layer (models, ORM) Version: master
Severity: Normal Keywords:
Cc: django@…, anubhav9042@… Triage Stage: Ready for checkin
Has patch: yes Needs documentation: no
Needs tests: no Patch needs improvement: no
Easy pickings: no UI/UX: no

Description

If a manager is passed in as the first argument to get_object_or_404, _get_queryset will convert it into a queryset via manager.all().
This means that an overridden get method on the manager passed to get_object_or_404 will not be called. This is rather unintuitive.

# In django.shortcuts __init__.py
def _get_queryset(klass):
    """
    Returns a QuerySet from a Model, Manager, or QuerySet. Created to make
    get_object_or_404 and get_list_or_404 more DRY.
    """
    if isinstance(klass, QuerySet):
        return klass
    elif isinstance(klass, Manager):
        manager = klass
    else:
        manager = klass._default_manager
    return manager.all()


def get_object_or_404(klass, *args, **kwargs):
#...
queryset = _get_queryset(klass)
    try:
        return queryset.get(*args, **kwargs)
#...

Perhaps it should just be return manager instead of manager.all().

Change History (13)

comment:1 Changed 7 years ago by thatch

Component: UncategorizedDatabase layer (models, ORM)
Needs documentation: unset
Needs tests: unset
Patch needs improvement: unset
Triage Stage: UnreviewedDesign decision needed

comment:2 Changed 5 years ago by Chris Beaven

Severity: Normal
Type: Bug

comment:3 Changed 5 years ago by ccrisan

Any updates on this bug? So far the only resolution I've found is to use my own get_object_or_404() function.

comment:4 Changed 5 years ago by Chris Beaven

If there were any updates on the bug, you'd see them here.

Since it sounds like you're already working with code to work around this issue, perhaps you'd care to produce a patch and test case? That's the kind of thing that gets things moving.

At the very least, start a discussion on the django-dev mailing list (which is a good idea anyway, since this is sitting in the design decision stage).

Last edited 5 years ago by Chris Beaven (previous) (diff)

comment:5 Changed 5 years ago by Aymeric Augustin

UI/UX: unset

Change UI/UX from NULL to False.

comment:6 Changed 5 years ago by Aymeric Augustin

Easy pickings: unset

Change Easy pickings from NULL to False.

comment:7 Changed 4 years ago by Anssi Kääriäinen

Triage Stage: Design decision neededAccepted

Sounds like a good change to me. I'd go a bit further: if klass has .get() method then use that. So:

    # If it is a model class, or anything else with ._default_manager
    if hasattr(klass, '_default_manager'):
        return klass._default_manager.all()
    return klass # If it is a manager or queryset, then this is OK. Even if it isn't then lets hope it has .get().

This would allow for true duct-typing, anything with .get() is OK, but Model subclasses which have .get() defined for other purposes will still continue to work.

The only question here is if this leads to confusing errors - having a method named .get() is somewhat likely. But I think the risk is worth it.

comment:8 Changed 3 years ago by Chris Streeter

Cc: django@… added

comment:9 Changed 3 years ago by ANUBHAV JOSHI

Cc: anubhav9042@… added
Owner: changed from nobody to ANUBHAV JOSHI
Status: newassigned

comment:10 Changed 3 years ago by ANUBHAV JOSHI

Owner: ANUBHAV JOSHI deleted
Status: assignednew

comment:11 Changed 6 months ago by Claude Paroz

Has patch: set

Anssi's suggestion implemented in that PR.

comment:12 Changed 6 months ago by Tim Graham

Triage Stage: AcceptedReady for checkin

comment:13 Changed 6 months ago by Claude Paroz <claude@…>

Owner: set to Claude Paroz <claude@…>
Resolution: fixed
Status: newclosed

In 12ba20d8:

Fixed #10532 -- Relaxed hard-type checking in get_object/list_or_404 shortcuts

Thanks Anssi Kääriäinen for the patch suggestion, and Tim Graham for the review.

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