Form validation in view class

• In the class view, implement form_valid(self, form) method

  File : book/views.py

  class AuthorCreate(CreateView):
      ...
  
      def form_valid(self, form):
          data = self.request.POST
          first_name = data.get('first_name')
          last_name = data.get('last_name')
          query = Author.objects.filter(
              first_name=first_name, last_name=last_name)
          authors = query.all()
          if len(authors) > 0:
              form.errors['input invalid'] = 'Author is already exist.'
              return self.form_invalid(form)
          return super(AuthorCreate, self).form_valid(form)

• If invalid, set form.errors[] and return self.form_invalid(form)

• The tricky part is how to show in the template.

  File : book/templates/book.author_form.html

  {{% load dict_key %}}
  ...
  <form method="post">{{% csrf_token %}}
  
    {{% if form.errors %}}
    <div class="mt-3 mb-3">
      {{%for k in form.errors %}}
      <div class="text-danger">
        {{ form.errors|dict_key:k }}
      </div>
      {{% endfor %}}
    </div>
    {{% endif %}}
    ...
  </form>

  The validation messages are generic and allow to take more than one. In order to display them, customized filter dict_key is applied.

• dict_key was learned from stackoverflow.

  File : book/templatetags/dict_key.py

  ``` python from django import template from django.template.defaultfilters import register

register = template.Library()

@register.filter(name='dict_key') def dict_key(d, k): '''Returns the given key from a dictionary.''' return d[k]

```