Django视图撤销了我的代码已实现的目标

Question

My model:

My 'event' references several 'items' through the following declaration:

items = models.ManyToManyField('Item')

My Form:

There are lots of items that I list in a bootstrap multi-select widget. To save time, I added a checkbox to the form that will add the descendants of the selected 'items' to my 'event' as well.

addToChildren = forms.BooleanField(required=False, label="Add event to descendants of selected item")

My View:

Once the form is submitted, I add the descendants with the following code:

class EventUpdate(UpdateView):
    #declared model, formclass and success url, but left it off for the question

    def form_valid(self, form):
        event = form.save()
        if form.cleaned_data['addToChildren'] == True:  #add to children if told to do so.
            print("items before save")
            print(self.object.items.all())
            for x in range(0,form.cleaned_data['items'].count()):
                itm = form.cleaned_data['items'][x]
                for descendant in itm.get_descendants():
                    self.object.items.add(descendant)#deletes when updated
            print("items after save")
            print(self.object.items.all())
        return super(EventUpdate, self).form_valid(form)

My Problem:

The print statements clearly show that the descendants of the selected items in are getting added to self.object (my event object).

The issue is that the return statement disregards my changes, adds selected items to my event, and removes all unselected items from my event. I would like that to stop.

Is there a way to append information to form.cleaned_data from a django view?

Answer 1

In your method you save the object, then take the related instances in the items field and add their dependents. But when you call the super method, Django will again save the form - including the many-to-many related objects, but it won't know about the ones you added so will overwrite them with only the selected ones.

Generally your desired behaviour seems a bit strange, but you can preserve it by not calling the super method at all. Apart from saving, the main thing the default implementation does is redirect to the success URL. So, you should replace that super call with a line that does that explicitly:

return HttpResponseRedirect(self.get_success_url())