#11527: Documentation and testing for F() assignment to model attributes
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Reporter: zacharyvoase | Owner: nobody
Status: new | Milestone: 1.1
Component: Database layer (models, ORM) | Version: SVN
Keywords: | Stage: Unreviewed
Has_patch: 0 |
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Add explicit documentation and regression tests for the use of
`django.db.models.F()`-expressions when assigning directly to attributes
on model instances (as opposed to just using them in batch `update()`
calls).
The pattern goes something like this:
{{{
>>> from django.db.models import F
>>> from myapp.models import MyModel
>>> obj = MyModel(count=1)
>>> obj.save()
>>> obj.count
1
>>> obj.count = F('count') + 2
>>> obj.save()
>>> obj = MyModel.objects.get(pk=obj.pk) # Necessary to reload here, as
the `count` attribute will still be an Expression object.
>>> obj.count
3
}}}
This should ''not'' work on records which do not already exist, since
`F()`-expressions only work in `UPDATE` queries.
It's also important for this to work with any pre-save and post-save
signal handlers defined in any of the django.contrib apps.
--
Ticket URL: <http://code.djangoproject.com/ticket/11527>
Django <http://code.djangoproject.com/>
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