使用commit = False保存的对象，仍然保存

Question

I have a very big model, with steps form. So I decided on each page get previous object and update his attributes in form. In first form I do:

def save(self, commit=False):
        obj = super(FirstForm, self).save(commit=False)
        obj.id = 999999999
        self.request.session['obj'] = pickle.dumps(obj)
        self.request.session.save()
        return obj

Id is required by mtm. So I set default one.

Then on last step in view I do:

obj = self.request.session.get('obj')
obj = pickle.loads(obj)
obj.id = None # remove temporary id
obj.save()

But Django save two objects. One normal object and one empty with id 999999999 . Why ?

I tried do:

obj = super(FirstForm, self).save(commit=False)

obj.id = 999999999
self.request.session['obj'] = pickle.dumps(obj)
self.request.session.save()
obj.delete()

But it didn't help.

Answer 1

This likely happens because the id field is used as a primary key for your model. When you set id to None , and then save the object, it'll actually create a new object with an id that's iterated sequentially from the previous last object.