CODEWITHSUNDEEP
pythondjangodjango-views
nassim
nassim

Reputation: 1555

django "<User: user556>" needs to have a value for field "id" before this many-to-many relationship can be used

I'm trying to save a M2M object ( set it to a default value which is the one with id = 1 ).

The problem I'm getting the following error:

"<User: user556>" needs to have a value for field "id" before this many-to-many relationship can be used.

I looked at previous feeds that covered the same error but no one explained when it happens in the form_valid function as it happened to me

My code is as follows :

  def form_valid(self,form):

    instance = form.instance
    instance.groups.set(1)
    instance.save()
    return super(UserCreateView,self).form_valid(form)

Upvotes: 2

Views: 489

Answers (1)

willeM_ Van Onsem
willeM_ Van Onsem

Reputation: 477065

You first need to save your instance, such that it has a primary key, otherwise you can not create a record in the junction table.

You thus implement this with:

from django.http import HttpResponseRedirect

    def form_valid(self,form):
        instance = form.save()
        instance.groups.set(1)
        return HttpResponseRedirect(self.get_success_url())

returning a HttpResponseRedirect is necessary here since a super().form_valid() will save the form again to the database, and will also set the groups to the ones specified in the form.

Upvotes: 2

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