Django: instance needs to have a primary key value before a many-to-many relationship

Question

This is my model

class Business(models.Model):
    business_type = models.ManyToManyField(BusinessType)
    establishment_type = models.ForeignKey(Establishm         


        

Answer 1

If anyone is out there still looking for answer to this, I was having the same issue and could not find a solution anywhere.

Here is where I had gone wrong: In my model, I was overriding the save() method in order to not persist data to my database. It seems obvious in retrospect, but overriding the save() method was causing the issue because my primary key was never actually being generated.

Good luck!

Answer 2

try it with this order:

if business.is_valid():
            busi = business.save(commit=False)
            et = EstablishmentType.objects.get(id=6)
            busi.establishment_type = et
            busi.save() #with commit == true
            bt = BusinessType.objects.get(id=6)
            busi.business_type = bt
            busi.save() #here you save many to many

Answer 3

You need to save the instance of the model before adding any m2m fields. Remember you have to add the m2m field with the .add() method, not assign it directly to the field as you are doing.

if business.is_valid():
    busi = business.save(commit=False)
    et = EstablishmentType.objects.get(id=6)
    busi.establishment_type = et
    busi.save()
    bt = BusinessType.objects.get(id=6)
    busi.business_type.add(bt)

Note that the save_m2m method is available on the modelform object when you do form_obj.save(commit=False). If the model form was given m2m data, you should use the save_m2m method. If you want to assign it manually like you're doing, you need to add it separately like my code above.

Answer 4

Save busi before attempting to assign to busi.business_type.