CODEWITHSUNDEEP
django
Houman
Houman

Reputation: 66320

How to save M2M Field in a formset when commit=False

deals_formset_factory = modelformset_factory(Deal, form=DealCForm, extra=1)    
attached_deals_formset = deals_formset_factory(request.POST, prefix='deals')

Since some fields of my Deal model are not shown in the form and hence can't be set by the user (but the M2M field is shown and can be set by the user), I can't just do a 

for fm in attached_deals_formset:                
    if fm.has_changed(): 
       fm.save()

since it would break.

So theoretically the idea in such situations is to do

deal = fm.save(commit=False)
...
deal.save()

but this doesn't save my M2M field inside deal. The Through table remains untouched. What is the best approach to solve this?

class Deal(models.Model):            
    deal_id             = UUIDField()
    ....
    sales_item          = models.ManyToManyField(SalesItem)

Upvotes: 1

Views: 2393

Answers (1)

Houman
Houman

Reputation: 66320

I found the solution, there is no need to override the save method.

Another side effect of using commit=False is seen when your model has a many-to-many relation with another model. If your model has a many-to-many relation and you specify commit=False when you save a form, Django cannot immediately save the form data for the many-to-many relation. This is because it isn't possible to save many-to-many data for an instance until the instance exists in the database.

To work around this problem, every time you save a form using commit=False, Django adds a save_m2m() method to your ModelForm subclass. After you've manually saved the instance produced by the form, you can invoke save_m2m() to save the many-to-many form data

Source

After deal.save() simply:

fm.save_m2m()

Upvotes: 3

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