Overriding Choices for a field in the Form not working when using ModelForm.

[Swaroop P]

Hi All

Facing the following issue after migrating to 3.2.

Example:

class SomeModel(models.Model):
       field1 = models.CharField(choices=[])

class SomeModelForm(forms.ModelForm):

     __init__(*args, **kwargs):
         super().__init__(*args **kwargs)
         self.fields['field1'].choices = <some choices dynamically generated>

    class Meta:
         model = SomeModel
         fields = [ 'field1' ]

In the above case any choice selected is shown with the error "not a valid choice" this is happening because model fields is revalidated again in modelform._post_clean() function.

Intermediate solution is to remove choices from modelfield and reinitalize field in form init wiht dynamic choices. But In previous versions We had choices to only override some attributes of a field rather than reinitalizing whole field.

Thanks

[Mariusz Felisiak]

Thanks for the report, it was changed in 16a5a2a2c8d8dbf9cc3e033dd84b986bcaadb963, however it's ​documented that:

For each model field that has choices set, Django will add a method to retrieve the human-readable name for the field’s current value. See get_FOO_display() in the database API documentation.

Note that choices can be any sequence object – not necessarily a list or tuple. This lets you construct choices dynamically. But if you find yourself hacking choices to be dynamic, you’re probably better off using a proper database table with a ForeignKey. choices is meant for static data that doesn’t change much, if ever.''

choices=[] means that it's set, if you want to get the previous behavior without any validation you shouldn't define choices on a model field, or set choices=None.