DEP Draft - Django Forms API Rewrite

forms.py

"""
Proposed New Forms API, not currently possible in Django Forms API (as of 2.0)
"""
from django.forms import ModelForm, ModelFormListField
from .models import Author, Book

# Make this work like serailization relationships in Django Rest Framework
# http://www.django-rest-framework.org/api-guide/relations/
# or relationships in WTForms 
# http://wtforms-alchemy.readthedocs.io/en/latest/relationships.html#one-to-many-relations
class BookForm(ModelForm):
    class Meta:
        model = Book
        fields = ['name', 'published_date']


class AuthorWithWorksForm(ModelForm):
    works = ModelFormListField(BookForm)
    
    class Meta:
        model = Author
        fields = ['name', 'works']

                  
# Allow for overrides on the form Meta rather than modification on __init__
# follows WTForms http://wtforms-alchemy.readthedocs.io/en/latest/configuration.html
from django.forms.widgets import TextArea
from .validators import validate_in_past

class AuthorOnlyForm(ModelForm):
    class Meta:
        model = Author
        fields = ['name', 'birth_date']
        field_args = {
            'name': {
                'widget': TextArea
            },
            'birth_date': {
                'required': True,
                'validators': [validate_in_past]
            }
        }

# Provide a means for the form to be client-side validation aware
# Since there's no standard, this very naive implementation may not scale
# Here's an implementation of Parsley.js through the new proposed API
# http://parsleyjs.org/doc/index.html#usage-field
from django.utils.timezone import now

class BookForm(ModelForm):
    class Meta:
        model = Book
        fields = ['name', 'published_date']
        field_args = {
            'name': {
                'widget_attrs': {
                    'data-parsley-minlength':'4'
                }
            },
            'birth_date': {
                'required': True,
                'validators': [validate_in_past],
                'widget_attrs': {
                    'data-parsley-max': now().astimezone().date().isoformat()
                }
            }
        }
        

models.py

from django.db import models


class Author(models.Model):
    name = models.CharField(max_length=255)
    birth_date = models.DateField(blank=True, null=True)

    def __str__(self):
        return self.name


class Book(models.Model):
    name = models.CharField(max_length=255)
    published_date = models.DateField(blank=True, null=True)
    authors = models.ManyToManyField(
        Author,
        on_delete=models.SET_NULL,
        related_name='works'
    )
    
    def __str__(self):
        return self.name
    

Hi @raiderrobert, I don't think this needs a DEP, it looks more like 3 independent tickets to me.

1/ is basically to turn InlineFormset into a form field. I quite like the idea.

2/ is the wontfixed ticket #17924 and related to #20000.

With hindsight I regret not pushing harder for #17924 and settling for #20000. DRF allowing this and being so widely popular certainly leads to people assuming Django forms works the same. Using this feature extensively with DRF I often feel frustrated not having it for forms.

One of the challenge with this ticket will be how to provide a consistent API as Carl mentioned in https://code.djangoproject.com/ticket/20000#comment:14 : widgets, label, help_text and error_messages, all have first level attributes on the Meta object, and deprecating them would be way too disruptive.

The process for a wontfixed ticket is the take it to the mailing list.

3/ I'm guessing widget_attrs is targeting the <input> tag in the generated HTML? Personally I'm not fond of the tight coupling of Python fields and HTML rendering, I prefer to look at form fields as a description of the data at a high level, then templates should have the whole object available to decide how to render the appropriate widget.

'birth_date': {
    'widget_attrs': {
        'data-parsley-max': now().astimezone().date().isoformat()
    }
}

Imo would be better solved with:

'birth_date': {
    'max':  now().astimezone().date()
}

{{ form.birth_date|add_attrs('data-parsley-max', form.birth_date.max.isoformat()) }}

Of course that's much harder to do with DTL than Jinja2, and currently form.birth_date is a BoundField rather than the actual field, but you get the idea.