Django Forms and CRUD

Source: MDN Tutorial - Working with Forms

Django can utilize HTML forms to create, update and delete model instances.

Because Django is so cool, it also includes a Django Forms framework for taking care of most of the heavy lifting when working with forms.

HTML Forms

Consider an HTML form:

<!-- From MDN: -->
<form action="/team_name_url/" method="post">
    <label for="team_name">Enter name: </label>
    <input id="team_name" type="text" name="name_field" value="Default name for team.">
    <input type="submit" value="OK">
</form>

In the above example, action determines where a form sends its data upon submission, while method determines what kind of request the data will be contained in.

The data gets sent to the server, and a bunch of stuff has to happen, such as validation, sanitation, feed-back to user, etc. It can be a lot of work. Django makes it less work.

Django Form Handling

Django’s form handling is pretty similar to how we normally render pages. A request is received to a view, the view executes necessary functions, and a template is rendered to the page.

Most specifically:

1. The form is displayed the first time it is requested.
2. Data is received from a form submission
3. Data is cleaned and validated
4. If any data is invalid, the form is re-displayed with user populated values and error messages.
5. If all data is valid, actions are performed accordingly
6. Once all actions are complete, the user is redirected.

Django Forms

Forms can be made in Django using either functional views or Form classes.

MDN Functional View example

import datetime

from django.contrib.auth.decorators import login_required, permission_required
from django.shortcuts import get_object_or_404
from django.http import HttpResponseRedirect
from django.urls import reverse

from catalog.forms import RenewBookForm

@login_required
@permission_required('catalog.can_mark_returned', raise_exception=True)
def renew_book_librarian(request, pk):
    """View function for renewing a specific BookInstance by librarian."""
    book_instance = get_object_or_404(BookInstance, pk=pk)

    # If this is a POST request then process the Form data
    if request.method == 'POST':

        # Create a form instance and populate it with data from the request (binding):
        form = RenewBookForm(request.POST)

        # Check if the form is valid:
        if form.is_valid():
            # process the data in form.cleaned_data as required (here we just write it to the model due_back field)
            book_instance.due_back = form.cleaned_data['renewal_date']
            book_instance.save()

            # redirect to a new URL:
            return HttpResponseRedirect(reverse('all-borrowed') )

    # If this is a GET (or any other method) create the default form.
    else:
        proposed_renewal_date = datetime.date.today() + datetime.timedelta(weeks=3)
        form = RenewBookForm(initial={'renewal_date': proposed_renewal_date})

    context = {
        'form': form,
        'book_instance': book_instance,
    }

    return render(request, 'catalog/book_renew_librarian.html', context)

MDN Class example

from django.forms import ModelForm

from catalog.models import BookInstance

class RenewBookModelForm(ModelForm):
    def clean_due_back(self):
       data = self.cleaned_data['due_back']

       # Check if a date is not in the past.
       if data < datetime.date.today():
           raise ValidationError(_('Invalid date - renewal in past'))

       # Check if a date is in the allowed range (+4 weeks from today).
       if data > datetime.date.today() + datetime.timedelta(weeks=4):
           raise ValidationError(_('Invalid date - renewal more than 4 weeks ahead'))

       # Remember to always return the cleaned data.
       return data

    class Meta:
        model = BookInstance
        fields = ['due_back']
        labels = {'due_back': _('Renewal date')}
        help_texts = {'due_back': _('Enter a date between now and 4 weeks (default 3).')}

Additional Resources

MDN: Creating a Home Page and Generic List and Detail Views