title: Django CheckboxSelectMultiple() widget - Form widget value not selected after saving data options
body: <p>How to can I work with multiple select options and make these options selected to stay selected ?</p>
  
  <p>Some application? 
  Should I use any JS?</p>
  
  <p>Is possible that my approach may be incomplete or 
  miss something ...?</p>
  
  <p>Context</p>
  
  <p>I have the following model:</p>
  
  <pre><code>class AcademicPeople(models.Model):
  
      CATHEDRAL_PROFESSOR = 'CATHEDRAL'
      RESEARCH_PROFESSOR = 'RESEARCH'
      INSTITUTIONAL_DIRECTIVE = 'DIRECTIVE'
  
      OCCUPATION_CHOICES = (
          (CATHEDRAL_PROFESSOR, 'Cathedral Professor'),
          (RESEARCH_PROFESSOR, 'Research Professor'),
          (INSTITUTIONAL_DIRECTIVE, 'Institutional Directive'),
      )
  
      occupation = models.CharField(
          max_length=255,
          blank = False,
      )
  </code></pre>
  
  <p>In the <code>forms.py</code> I have:</p>
  
  <pre><code>from .models import
  from django.forms.widgets import CheckboxSelectMultiple
  
  class AcademicPeopleForm(forms.ModelForm):
      title = "Details"
      occupation = forms.MultipleChoiceField(
          required=False,
          label='Occupation',
          widget=CheckboxSelectMultiple(),
          choices=AcademicPeople.OCCUPATION_CHOICES
      )
  
      class Meta:
          model = AcademicPeople
          fields = ('occupation',)
  </code></pre>
  
  <p><strong>UPDATE</strong></p>
  
  <p>My view is very basic, is the following:</p>
  
  <pre><code>class AccountSettingsUpdateView(LoginRequiredMixin, UpdateView):
      model = AcademicPeople
      form_class = AcademicPeopleForm
      success_url = reverse_lazy('dashboard')
      context_object_name = 'preferences'
  </code></pre>
  
  <p>When I go to my template using the browser, I get the checkbox select multiple rendered in checkboxes, I select some options and when I save, these options selected does not show their value.</p>
  
  <p><a href="https://i.stack.imgur.com/p4dI6.gif" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/p4dI6.gif" alt="enter image description here"></a></p>