[Django] #18357: BaseGenericInlineFormSet in Django Admin does not set generic foreign key fields when constructing form

[Django]

#18357: BaseGenericInlineFormSet in Django Admin does not set generic foreign 
key
fields when constructing form
--------------------------------------+--------------------
     Reporter:  buettgenbach@…        |      Owner:  nobody
         Type:  Bug                   |     Status:  new
    Component:  contrib.contenttypes  |    Version:  1.3
     Severity:  Normal                |   Keywords:
 Triage Stage:  Unreviewed            |  Has patch:  0
Easy pickings:  0                     |      UI/UX:  0
--------------------------------------+--------------------
 For a BaseInlineFormSet in _construct_form the fk value is set in order to
 do validation.

 {{{
     def _construct_form(self, i, **kwargs):
         ...
         # Set the fk value here so that the form can do it's validation.
         setattr(form.instance, self.fk.get_attname(), self.instance.pk)
         return form
 }}}

 Something similar is missing for BaseGenericInlineFormSet. Actually it has
 been removed in
 
[https://github.com/django/django/commit/856a39e841080abc34e8ae3bb2b20f780c33762d#L0R329].
 As a consequence during model based cleaning the generic foreign key
 attribute cannot be accessed/cleaned because it is not set. Assume the
 following fictional code:

 {{{
 class Poll(models.Model):
     question = models.CharField(max_length=200)
     pub_date = models.DateTimeField('date published')

 class GenericChoice(models.Model):
     content_type = models.ForeignKey(ContentType)
     content_id = models.PositiveIntegerField()
     content = generic.GenericForeignKey('content_type', 'content_id')
     choice = models.CharField(max_length=200)
     votes = models.IntegerField()

     def clean(self):
         if self.votes > 10 and self.content.question == 'Don't allow more
 than 10 votes':
             raise ValidationError('Test')
 }}}

 This results in an NoneType error since self.content is None.
 With something like this in BaseGenericInlineFormSet it could be fixed:

 {{{
     def _construct_form(self, i, **kwargs):
         # Avoid a circular import.
         from django.contrib.contenttypes.models import ContentType
         form = super(BaseGenericInlineFormSet, self)._construct_form(i,
 **kwargs)
 #        if self.save_as_new:
 #            # Remove the key from the form's data, we are only creating
 new instances.
 #            form.data[form.add_prefix(self.ct_fk_field.name)] = None
 #            form.data[form.add_prefix(self.ct_field.name)] = None

         # Set the GenericForeignKey value here so that the form can do its
 validation.
         setattr(form.instance, self.ct_fk_field.attname, self.instance.pk)
         setattr(form.instance, self.ct_field.attname,
 ContentType.objects.get_for_model(self.instance).pk)
         return form
 }}}

 But this would only fix those cases where the parent model already exists
 (Admin edit). If the parent does not exist (for example when creating a
 new Poll with some GenricChoice inline sets) the generic foreign key field
 cannot be accessed since content_id is not set (and the _cache_content is
 not set, too). Using a simple BaseInlineFormSet this is achieved by
 setting the foreing key object through the InlineForeignKeyField which is
 instantiated with the foreign key object during add_fields in
 BaseInlineFormSet.

-- 
Ticket URL: <https://code.djangoproject.com/ticket/18357>
Django <https://code.djangoproject.com/>
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