#22224: Non-nullable blank string-based model field validation doesn't prevent
or
clean `None`
-----------------------------------------+------------------------
Reporter: charettes | Owner: nobody
Type: Bug | Status: new
Component: Uncategorized | Version: master
Severity: Normal | Keywords:
Triage Stage: Unreviewed | Has patch: 0
Needs documentation: 0 | Needs tests: 0
Patch needs improvement: 0 | Easy pickings: 0
UI/UX: 0 |
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Since
[https://docs.djangoproject.com/en/dev/ref/models/fields/#django.db.models.Field.null
we discourage the use of NULLable string-based fields] the assumed way of
holding text that might be empty would be to use the `blank` option.
In this case I would expect `full_clean` to raise a `ValidationError` when
an empty non-nullable field is assigned `None`:
{{{#!python
from django.db import models
class A(models.Model):
b = models.CharField(blank=True)
a = A(b=None)
a.full_clean() # Passes
a.save() # Integrity error
}}}
Unfortunately specifying `blank=True` disable all validation against the
`b` field, leading to database integrity error upon calling `save()`. The
obvious solution here would be to override `A.clean` to convert `b` to an
empty string when it equals `None` but it strikes me as a non trivial
change for a quite common use case: correctly allowing a string-based
field to be empty.
This is not an issue when cleaning data retrieved from the usual
`application/form-url-encoded` `request.GET` or `request.POST` since an
empty value is always represented by the empty string. However, in the
case of an `application/json` encoded payload one may either provide
`None` or `''` (`null` or `''`) to express emptiness. Which will trigger
the issue described above.
Attaching a patch that special case the `empty_values` of non-nullable
string based fields based on the `empty_strings_allowed` flag. All tests
pass on Py7/SQLite3.
--
Ticket URL: <https://code.djangoproject.com/ticket/22224>
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