Are ModelForms in django used only for POSTing?

Question

ModelForms are a nice way to prevent repeating the definitions of models one creates. What I would like to do is take advantage of that feature and use it for more than just processing POST requests. I use forms a lot for validation.

Example:

Say you have a User model with the fields (email, password, first_name, last_name). The email field is unique and an index.

UserCreationForm: uses all fields, fails validation if the email already exists. Processes POST requests UserUpdateForm: the same model, but doesn't allow to change the email. Because this field is excluded no issues there. UserAuthenticationForm: includes only the email and password fields. The problem is, this should be used for authentication and validation fails because the email already exists.

Is there a way I can do this? That is, have the UserAuthenticationForm skip the email checking.

Thank you.

It would be a very odd tweak that might affect your code later, coding the form for authentication isn't that hard. You will be better following programming principle *separation of concerns* http://en.wikipedia.org/wiki/Separation_of_concerns and letting each part of your software focus on its own objective. — Paulo Bu, May 15 '13 at 14:48
Hmm.. I don't think the logic separation is the issue. The form is doing something very spefic. — André Fratelli, May 15 '13 at 14:54
What I meant in the comment was the same you did in your answer. You have a form for creating/updating objects, don't use it for log users. Use it just for what it was created. — Paulo Bu, May 15 '13 at 15:00

Adrián · Accepted Answer · 2013-05-15T14:55:05.523

0

ModelForms are for creating/updating objects. Authentication doesn't modify the model instance (the User), therefore use a normal form instead.

From the docs:

The save() method

Every form produced by ModelForm also has a save() method. This method creates and saves a database object from the data bound to the form. A subclass of ModelForm can accept an existing model instance as the keyword argument instance; if this is supplied, save() will update that instance. If it’s not supplied, save() will create a new instance of the specified model.

If you weren't going to use this save(), method and you don't need most of the model fields either (only username/email and password), you would be throwing away most of the functionality offered by the ModelForm, so why would you use it in the first place?

edited May 15 '13 at 14:55

answered May 15 '13 at 14:43

Adrián

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I concur with your answer, but I think he ain't planning to use `safe`, just `validate. – Paulo Bu May 15 '13 at 14:51
Still, how do I use it for updating objects? It still says the email already exists. – André Fratelli May 15 '13 at 14:53
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You pass it the instance of the already existent object like this: `form = Form(request.POST, instance=db_object)` – Paulo Bu May 15 '13 at 14:54
Hmm.. I still get "This field is required." is it supposed to? – André Fratelli May 15 '13 at 15:10
@AndréFratelli `class Meta: model = User exclude = ['email']` in 3 lines of course. – Adrián May 15 '13 at 15:22
Adrián, not quite what I meant. If I do that then I can't update the email field. I want to allow the user to update only *some* fields. If the request includes an email address, then the address is updated, if the address is not in the request, then it remains unchanged, but still accepting validation. Can I do that? – André Fratelli May 15 '13 at 15:29
@AndréFratelli see http://stackoverflow.com/questions/1134667/django-required-field-in-model-form then ;) – Adrián May 15 '13 at 15:32
That does it! Thanks a lot ;) – André Fratelli May 15 '13 at 16:14

Are ModelForms in django used only for POSTing?

1 Answers1