.

anatomy/forms.py

@@ -90,6 +90,43 @@ class AnatomyQuestionForm(ModelForm):
             queryset=Exam.objects.all(),
         )
 
+
+        # Only in case we build the form from an instance
+        # (otherwise, 'toppings' list should be empty)
+        if kwargs.get('instance'):
+            # We get the 'initial' keyword argument or initialize it
+            # as a dict if it didn't exist.
+            initial = kwargs.setdefault('initial', {})
+            # The widget for a ModelMultipleChoiceField expects
+            # a list of primary key for the selected data.
+            initial['exams'] = [t.pk for t in 
+                kwargs['instance'].exams_set.all()]
+
+        ModelForm.__init__(self, *args, **kwargs)
+
+    def save(self, commit=True):
+        # Get the unsaved Pizza instance
+        instance = ModelForm.save(self, False)
+
+        # Prepare a 'save_m2m' method for the form,
+        old_save_m2m = self.save_m2m
+
+        def save_m2m():
+            old_save_m2m()
+            # This is where we actually link the pizza with toppings
+            instance.exams_set.clear()
+            for exam in self.cleaned_data['exams']:
+                instance.exams_set.add(exam)
+
+        self.save_m2m = save_m2m
+
+        # Do we need to save all changes now?
+        if commit:
+            instance.save()
+            self.save_m2m()
+
+        return instance
+
     class Meta:
         model = AnatomyQuestion