title: Add data to ModelForm object before saving
body: <p>Say I have a form that looks like this:</p>
  
  <p><strong>forms.py</strong></p>
  
  <pre><code>class CreateASomethingForm(ModelForm):
      class Meta:
          model = Something
          fields = ['field2', 'field3', 'field4']
  </code></pre>
  
  <p>I want the form to have these three fields. However my <code>Something</code>class also has <code>field1</code>. My question is - how do I add data to <code>field1</code>, if I am not using the <code>ModelForm</code> to collect the data. I tried doing something like this, but it isn't working and I am unsure on the proper way to solve this:</p>
  
  <p><strong>views.py</strong></p>
  
  <pre><code>def create_something_view(request):
      if (request.method == 'POST'):
          # Create an object of the form based on POST data
          obj = CreateASomething(request.POST)
          # ** Add data into the blank field1 ** (Throwing an error)
          obj['field1'] = request.user
          # ... validate, save, then redirect 
  </code></pre>
  
  <p>The error I receive is:</p>
  
  <pre><code>TypeError: 'CreateAClassForm' object does not support item assignment
  </code></pre>
  
  <p>In Django, what is the proper way to assign data to a <code>ModelForm</code> object before saving?</p>