title: Save m2m in FormView django
body: <p>I'm trying to save a m2m field in a <code>FormView</code>.</p>
  
  <p>Here is my code:</p>
  
  <pre><code>class ProductorPropietarioView(FormView):
      form_class = FormPropietario
      success_url = '/'
      template_name = 'productores/propietario.html'
  
      def form_valid(self,form):      
          form.save(commit=False)
          form.save()
          form.save_m2m()
          return super(ProductorPropietarioView,self).form_valid(form)
  </code></pre>
  
  <p>models.py</p>
  
  <pre><code>class Persona(models.Model):
      predio = models.ForeignKey(InfoPredioGeneral,related_name='predio+')
      rol = models.ManyToManyField(RolPersona)
      tipo_identificacion = models.ForeignKey(TipoIdentificacion,related_name='tipo identificacion+',blank=True,null=True)
      numero_identificacion = models.CharField(max_length=100,blank=True,null=True)
  </code></pre>
  
  <p>forms.py</p>
  
  <pre><code>class FormPropietario(ModelForm):
      class Meta():
          model = Persona
          fields = '__all__'
  </code></pre>
  
  <p>I can't get this to work. I know that first I have to set False then save the form and then save the m2m. I already tried only with <code>form.save()</code></p>
  
  <p>What am I doing wrong?</p>