#25547: refresh_from_db leaves FieldFile with reference to db_instance
-------------------------------------+-------------------------------------
Reporter: vinnyrose | Owner: nobody
Type: Bug | Status: new
Component: Database layer | Version: 1.8
(models, ORM) | Keywords: refresh_from_db,
Severity: Normal | fieldfile
Triage Stage: Unreviewed | Has patch: 0
Easy pickings: 0 | UI/UX: 0
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#### models.py
{{{#!python
class Product(models.Model):
myfile = models.FileField(upload_to='folder')
}}}
##### elsewhere.py
{{{#!python
product = Product.objects.create(myfile='filename')
product.refresh_from_db()
assert id(product.myfile.instance) == id(product) # false
}}}
{{{product.file.instance}}} is actually {{{db_instance}}} which is used
internally in {{{refresh_from_db}}}.
This leads to strange results when trying to use {{{FieldFile.save}}} or
{{{FieldFile.delete}}}, since you would be modifying {{{db_instance}}}
instead of the intended {{{instance}}}. This also means any field that
uses a {{{descriptor_class}}} that returns an {{{attr_class}}} will have
this same issue, I've used this pattern for custom fields.
This could most simply be fixed in the {{{FileDescriptor}}} itself,
because frankly I don't see how this could be fixed for all cases in which
a field has reference to the {{{instance}}} from which it was instatianted
from. Perhaps a warning on {{{refresh_from_db}}} in the docs about this
risk?
--
Ticket URL: <https://code.djangoproject.com/ticket/25547>
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