Re: [Django] #20202: BaseModelForm uses model_to_dict to provide initial, causes problems for ModelChoiceField with non-pk to_field_name

[Django]

#20202: BaseModelForm uses model_to_dict to provide initial, causes problems for
ModelChoiceField with non-pk to_field_name
---+-
 Reporter:  valtron2000@…  |Owner:  nobody
 Type:  New feature|   Status:  closed
Component:  Forms  |  Version:  1.5
 Severity:  Normal |   Resolution:  duplicate
 Keywords: | Triage Stage:  Accepted
Has patch:  0  |  Needs documentation:  0
  Needs tests:  0  |  Patch needs improvement:  0
Easy pickings:  0  |UI/UX:  0
---+-
Changes (by bmispelon):

 * status:  new => closed
 * resolution:   => duplicate


Comment:

 Well as it turns out, this issue has already been reported.

 I'm marking this one as a duplicate. All further discussion should be done
 in the original ticket: #17657

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Re: [Django] #20202: BaseModelForm uses model_to_dict to provide initial, causes problems for ModelChoiceField with non-pk to_field_name

[Django]

#20202: BaseModelForm uses model_to_dict to provide initial, causes problems for
ModelChoiceField with non-pk to_field_name
---+
 Reporter:  valtron2000@…  |Owner:  nobody
 Type:  New feature|   Status:  new
Component:  Forms  |  Version:  1.5
 Severity:  Normal |   Resolution:
 Keywords: | Triage Stage:  Accepted
Has patch:  0  |  Needs documentation:  0
  Needs tests:  0  |  Patch needs improvement:  0
Easy pickings:  0  |UI/UX:  0
---+

Comment (by bmispelon):

 I made a first attempt at documenting the existing behavior:
 https://github.com/bmispelon/django/compare/ticket-20202

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Re: [Django] #20202: BaseModelForm uses model_to_dict to provide initial, causes problems for ModelChoiceField with non-pk to_field_name

[Django]

#20202: BaseModelForm uses model_to_dict to provide initial, causes problems for
ModelChoiceField with non-pk to_field_name
---+
 Reporter:  valtron2000@…  |Owner:  nobody
 Type:  New feature|   Status:  new
Component:  Forms  |  Version:  1.5
 Severity:  Normal |   Resolution:
 Keywords: | Triage Stage:  Accepted
Has patch:  0  |  Needs documentation:  0
  Needs tests:  0  |  Patch needs improvement:  0
Easy pickings:  0  |UI/UX:  0
---+
Changes (by valtron2000@…):

 * type:  Bug => New feature


Comment:

 I see, `to_field_name` is supposed to be mostly internal, because it's
 usually set by `ForeignKey.formfield`
 
(https://github.com/django/django/blob/master/django/db/models/fields/related.py#L1244).
 The only time the user has to provide it is if they're defining the field
 manually rather than though `Meta.fields`. I agree that this should be
 documented.

 However, my use case is: my FKs use the PK, but my models also have a uuid
 field. I don't want to expose PKs in the front end, so I was in the
 process of (as of now, incorrectly) using `to_field_name` to use the uuid
 for a bunch of fields. Therefore, I'm turning this into a feature request.

 I know that a lot of people currently use `model_to_dict` as it stands, so
 changing its behaviour isn't an option. It would be better to make a
 private `_get_initial_from_instance` that works the same but returns the
 instance instead of the PK for FK fields, and then it becomes the form
 field's responsibility to turn the instance into an HTML form field value.

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Re: [Django] #20202: BaseModelForm uses model_to_dict to provide initial, causes problems for ModelChoiceField with non-pk to_field_name

[Django]

#20202: BaseModelForm uses model_to_dict to provide initial, causes problems for
ModelChoiceField with non-pk to_field_name
---+
 Reporter:  valtron2000@…  |Owner:  nobody
 Type:  Bug|   Status:  new
Component:  Forms  |  Version:  1.5
 Severity:  Normal |   Resolution:
 Keywords: | Triage Stage:  Accepted
Has patch:  0  |  Needs documentation:  0
  Needs tests:  0  |  Patch needs improvement:  0
Easy pickings:  0  |UI/UX:  0
---+

Comment (by bmispelon):

 I've been digging a bit and now I'm not sure if this is technically a bug
 or not.

 The main problem is that since the `to_field_name` attribute is
 undocumented, what it's supposed to do is not exactly clear.

 The fact is that there is a (passing) test the issue you describe:
 
https://github.com/django/django/blob/master/tests/model_forms/tests.py#L1508-L1513

 Without documentation, a test is probably the next best thing to know the
 intended behavior.

 From the test, it looks like the form field's `to_field_name` should match
 the model field's `to_field`, which in your example is not the case (and
 causes the issue).

 Note that the test models is quite similar to your example (the difference
 being the existence of the `to_field` attribute):
 https://github.com/django/django/blob/master/tests/model_forms/models.py#L174

 So I'm leaving this as "Accepted", but I think the first thing to do would
 be to document `ModelChoiceField.to_field_name` and then make sure the
 implementation matches the documentation.

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Re: [Django] #20202: BaseModelForm uses model_to_dict to provide initial, causes problems for ModelChoiceField with non-pk to_field_name

[Django]

#20202: BaseModelForm uses model_to_dict to provide initial, causes problems for
ModelChoiceField with non-pk to_field_name
---+
 Reporter:  valtron2000@…  |Owner:  nobody
 Type:  Bug|   Status:  new
Component:  Forms  |  Version:  1.5
 Severity:  Normal |   Resolution:
 Keywords: | Triage Stage:  Accepted
Has patch:  0  |  Needs documentation:  0
  Needs tests:  0  |  Patch needs improvement:  0
Easy pickings:  0  |UI/UX:  0
---+
Changes (by bmispelon):

 * cc: bmispelon@… (added)
 * needs_docs:   => 0
 * needs_better_patch:   => 0
 * needs_tests:   => 0
 * stage:  Unreviewed => Accepted


Comment:

 This definitely looks like a bug but it might be a bit tricky to fix (it
 will at least require some changes to `model_to_dict`'s signature).

 As noted, the issue is that `model_to_dict` will always return the primary
 key of the model, not taking into account the field's `to_field_name`
 attribute.

 The problem is that `model_to_dict` does not have access to the form's
 fields: it only gets passed the instance, a list of strings corresponding
 to the model's fields present in the form, and a list of strings of the
 fields to exclude. Therefore, it has no way to access the `to_field_name`
 attribute and adjust the value accordingly.

 On a side-note, it seems that `ModelChoiceField.to_field_name` is
 completely undocumented, though there seem to be a few tests for it.

 This ticket could be a good excuse to finally document it.

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[Django] #20202: BaseModelForm uses model_to_dict to provide initial, causes problems for ModelChoiceField with non-pk to_field_name

[Django]

#20202: BaseModelForm uses model_to_dict to provide initial, causes problems for
ModelChoiceField with non-pk to_field_name
---+
 Reporter:  valtron2000@…  |  Owner:  nobody
 Type:  Bug| Status:  new
Component:  Forms  |Version:  1.5
 Severity:  Normal |   Keywords:
 Triage Stage:  Unreviewed |  Has patch:  0
Easy pickings:  0  |  UI/UX:  0
---+
 {{{
 class M(models.Model):
   slug = models.CharField(max_length = 5, unique = True)
   other = models.ForeignKey('M', blank = True, null = True)

 class F(forms.ModelForm):
   class Meta:
 model = M
 fields = ('other',)

   other = forms.ModelChoiceField(to_field_name = 'slug')

 def example():
   m1 = M.objects.create(slug = 'xyzzy')
   m2 = M.objects.create(slug = 'abcde', other = m1)
   form = F(instance = m2)

   # Prints m1.pk; should contain the model instance, instead,
   # so that the ModelChoiceField can actually get the to_field_name
 attribute
   print form.initial['other']

   # Prints this: (note that xyzzy isn't selected="selected")
   # Other:
   # -
   # M object
   # M object
   # 
   print form
 }}}

 There is a workaround: manually provide the correct field in the initial.

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Ticket URL: 
Django 
The Web framework for perfectionists with deadlines.

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