When and how to use Django CreateView

# When to use CreateView?

Django provides several class based generic views to accomplish common tasks. One among them is CreateView.

CreateView should be used when you need a form on the page and need to do a db insertion on submission of a valid form.

# CreateView is better than vanilla View

We will first write a vanilla view by subclassing View, and then modify the view to subclass CreateView instead of View.

CreateView is better than vanilla View in following ways:

Avoid boilerplate code
Succinct and more maintainable code.

# Vanilla View

We want to create a page with a book creation form.

# books/models.py
class Book(models.Model):
    title = models.CharField(max_length=100)
    isbn = models.CharField(max_length=100, unique=True)
    is_published = models.BooleanField(default=True)

    def __str__(self):
        return self.title

# books/forms.py
class BookCreateForm(forms.ModelForm):
    class Meta:
        model = Book

Vanilla view looks like:

# books/views.py
class BookCreateView(CreateView):
    def get(self, request, *args, **kwargs):
        context = {'form': BookCreateForm()}
        return render(request, 'books/book-create.html', context)

    def post(self, request, *args, **kwargs):
        form = BookCreateForm(request.POST)
        if form.is_valid():
            book = form.save()
            book.save()
            return HttpResponseRedirect(reverse_lazy('books:detail', args=[book.id]))
        return render(request, 'books/book-create.html', {'form': form})

Template code looks like:

<!--books/templates/books/book-create.html-->

<form action="." method="POST">

{% csrf_token %}

<table>

</table>
<button type="submit">SUBMIT</button>
</form>

With proper urlpattern, you should be able to see the book creation form.

from django.urls import path

from . import views

app_name = 'books'
urlpatterns = [
    path('create/', views.BookCreateView.as_view(), name='create'),
    path('<int:pk>/', views.BookDetailView.as_view(), name='detail'),
]

# Using CreateView

Vanilla view has a lot of boilerplate code.

Any object creation view will have a get() implementation for creating context and rendering the response. Similarly object creation view will have a post() implementation to do .save(). CreateView, which is a generic class based view, can avoid this boilerplate code.

class BookCreateView(CreateView):
    template_name = 'books/book-create.html'
    form_class = BookCreateForm

This change also needs that a get_absolute_url() be defined on the object which is being created. So we need to provide a get_absolute_url() on model Book.

class Book(models.Model):
    # More code
    def get_absolute_url(self):
        return reverse('books:detail', args=[self.id])

Refresh the page and you should still be able to achieve everything that was possible with vanilla view.

As you would have noticed, using a CreateView helped us avoid boilerplate get() and post() implementation. The code looks much more succinct as it only has few class attributes and there isn’t any function implementation.

# Adding initial data to CreateView

Assume we want to populate form’s title field with some initial data.

Modify BookCreateView to look like:

class BookCreateView(CreateView):
    template_name = 'books/book-create.html'
    form_class = BookCreateForm

    def get_initial(self, *args, **kwargs):
        initial = super(BookCreateView, self).get_initial(**kwargs)
        initial['title'] = 'My Title'
        return initial

This code has better separation of concern. There is a separate method for dealing with initial data.

Had we used a vanilla view, initial data code would have been part of get().

# Adding form kwargs to CreateView

Let’s add a user field to Book to track the user who creates a Book.

class Book(models.Model):
    title = models.CharField(max_length=100)
    isbn = models.CharField(max_length=100, unique=True)
    is_published = models.BooleanField(default=True)
    user = models.ForeignKey(User, on_delete=models.CASCADE, **NULL_AND_BLANK)

    def __str__(self):
        return self.title

    def get_absolute_url(self):
        return reverse('books:detail', args=[self.id])

Assume you don’t want to allow a user to create two books with same title. The title should be unique per user.

This validation needs writing a clean_title() method which would look like:

class BookCreateForm(forms.ModelForm):
    class Meta:
        model = Book
        exclude = ('user',)

    def __init__(self, *args, **kwargs):
        self.user = kwargs.pop('user')
        super(BookCreateForm, self).__init__(*args, **kwargs)

    def clean_title(self):
        title = self.cleaned_data['title']
        if Book.objects.filter(user=self.user, title=title).exists():
            raise forms.ValidationError("You have already written a book with same title.")
        return title

This needs that a user be supplied from view during form creation. This is where CreateView.get_form_kwargs() come into picture. Modify the view to look like:

class BookCreateView(CreateView):
    template_name = 'books/book-create.html'
    form_class = BookCreateForm

    def form_valid(self, form):
        self.object = form.save(commit=False)
        self.object.user = self.request.user
        self.object.save()
        return HttpResponseRedirect(self.get_success_url())

    def get_initial(self, *args, **kwargs):
        initial = super(BookCreateView, self).get_initial(**kwargs)
        initial['title'] = 'My Title'
        return initial

    def get_form_kwargs(self, *args, **kwargs):
        kwargs = super(BookCreateView, self).get_form_kwargs(*args, **kwargs)
        kwargs['user'] = self.request.user
        return kwargs

After this any logged in user wouldn’t be able to create two Books with same title.

# Our other posts on generic class views

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Thank you for reading the Agiliq blog. This article was written by Akshar on Jan 7, 2019 in django .

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