Django Experience #19 - Dica: O problema do readonly e validação no Django

Doc: https://docs.djangoproject.com/en/4.0/ref/forms/validation/#cleaning-a-specific-field-attribute

Considere a app todo e o campo description:

# todo/models.py
class Todo(models.Model):
    ...
    description = models.TextField('descrição', null=True, blank=True)
    ...

# todo/forms.py
from django import forms
from django.core.exceptions import ValidationError

from .models import Todo


class TodoForm(forms.ModelForm):
    required_css_class = 'required'

    class Meta:
        model = Todo
        fields = '__all__'

    def __init__(self, *args, **kwargs):
        super(TodoForm, self).__init__(*args, **kwargs)

        for field_name, field in self.fields.items():
            field.widget.attrs['class'] = 'form-control'

        # Remove a class de is_done.
        self.fields['is_done'].widget.attrs['class'] = None

        # Torna description somente leitura.
        self.fields['description'].widget.attrs['readonly'] = True

    # def clean(self):
    #     self.cleaned_data = super().clean()
    #     self.description = self.cleaned_data.get('description')
    #     self.label = self.fields["description"].label

    #     if self.description or self.description != self.instance.description:
    #         raise ValidationError(f'O campo {self.label} não pode ser editado!')

    #     return self.cleaned_data

    def clean_description(self):
        self.description = self.cleaned_data.get('description')
        self.label = self.fields["description"].label

        if self.description or self.description != self.instance.description:
            raise ValidationError(f'O campo {self.label} não pode ser editado!')

        return self.cleaned_data