Django forms

The Django Form class

At the heart of this system of components is Django’s Form class. In much the same way that a Django model describes the logical structure of an object, its behavior, and the way its parts are represented to us, a Form class describes a form and determines how it works and appears.

In a similar way that a model class’s fields map to database fields, a form class’s fields map to HTML form input elements. (A ModelForm maps a model class’s fields to HTML form input elements via a Form; this is what the Django admin is based upon.)

A form’s fields are themselves classes; they manage form data and perform validation when a form is submitted. A DateField and a FileField handle very different kinds of data and have to do different things with it.

A form field is represented to a user in the browser as an HTML “widget” - a piece of user interface machinery. Each field type has an appropriate default Widget class, but these can be overridden as required.

Building a form in Django

from django import forms

class NameForm(forms.Form):
    your_name = forms.CharField(label='Your name', max_length=100)

The view

from django.http import HttpResponseRedirect
from django.shortcuts import render

from .forms import NameForm

def get_name(request):
    # if this is a POST request we need to process the form data
    if request.method == 'POST':
        # create a form instance and populate it with data from the request:
        form = NameForm(request.POST)
        # check whether it's valid:
        if form.is_valid():
            # process the data in form.cleaned_data as required
            # ...
            # redirect to a new URL:
            return HttpResponseRedirect('/thanks/')

    # if a GET (or any other method) we'll create a blank form
    else:
        form = NameForm()

    return render(request, 'name.html', {'form': form})

Note

All form classes are created as subclasses of either django.forms.Form or django.forms.ModelForm. You can think of ModelForm as a subclass of Form. Form and ModelForm actually inherit common functionality from a (private) BaseForm class, but this implementation detail is rarely important.