Opened 5 years ago

Last modified 22 months ago

#26142 assigned New feature

Provide a way for model formsets to disallow new object creation

Reported by: Tim Graham Owned by: Parth Patil
Component: Forms Version: dev
Severity: Normal Keywords:
Cc: Triage Stage: Accepted
Has patch: yes Needs documentation: yes
Needs tests: no Patch needs improvement: yes
Easy pickings: no UI/UX: no


Model formsets don't provide a way to create an "edit only" view of objects. We see users trying to use extra=0 to accomplish this, but that's not reliable as extra is merely meant for the extra number of forms to display. You can add more forms with Javascript (or just send additional post data).

Attachments (1)

26142-test.diff (1.2 KB) - added by Tim Graham 5 years ago.

Download all attachments as: .zip

Change History (12)

comment:1 Changed 5 years ago by Tim Graham <timograham@…>

In 8e6a08e:

Refs #26142 -- Documented that Formset's extra=0 doesn't prevent creating objects.

comment:2 Changed 5 years ago by Tim Graham <timograham@…>

In 204d31c:

[1.9.x] Refs #26142 -- Documented that Formset's extra=0 doesn't prevent creating objects.

Backport of 8e6a08e937272f088902cdbec65a9f2e919783bf from master

comment:3 Changed 5 years ago by Mathias Rav

Owner: changed from nobody to Mathias Rav
Status: newassigned

comment:4 Changed 5 years ago by David Sanders

Doesn't max_num already allow this? Testing on master, if you have max_num set to 0 and validate_max to True, then the formset is effectively edit-only for existing objects. From the documentation:

max_num does not prevent existing objects from being displayed

Is there a corner case of functionality that's not covered by these two settings?

comment:5 Changed 5 years ago by Tim Graham

Yes, I think it's that sending data that references pks that don't appear in the queryset creates new objects for that data.

comment:6 Changed 5 years ago by David Sanders

Can you expand on that a little? Looking at the formset code, if the form number is less than the initial form count, it uses save_existing_object. Since validate_max prevents any forms above initial form count from being a valid formset, the only way a new object could be created is if save_existing_object could create new objects, which would be a bug in itself probably.

Playing with it in Chrome, providing a blank value for the PK of one of the objects in the formset will cause an error when trying to use to_python on the PK value since the value is blank and an integer is expected. Even if that didn't fail, it would fail to find the object by its PK in the queryset.

Providing a bogus value for the PK will also fail to look up in the queryset on the formset. This also occurs if you use a PK for an existing object that isn't in the queryset, which is good, otherwise you'd be able to modify objects outside the queryset which would be very bad.

So, I'm not sure I see the path where new objects can be created if validate_max is set and max_num is 0. Doesn't mean it's not there, but it's not immediately obvious how that could occur.

comment:7 Changed 5 years ago by Tim Graham

I don't think max_num=0 allows editing existing instances. Such a formset will fail with "Please submit 0 or fewer forms." won't it?

The idea I had to try to accomplish this is setting max_num=len(queryset) but I'm attaching a regression test demonstrating that an extra instance is created if the user edits the 'form-INITIAL_FORMS' form value.

Changed 5 years ago by Tim Graham

Attachment: 26142-test.diff added

comment:8 Changed 23 months ago by Parth Patil

Owner: changed from Mathias Rav to Parth Patil

Hey Mathias, I have started working on this ticket, hope it's not a problem that I'm assigning this to myself. Found no other to contact you so am directly assigning it.

I will try to make an edit_only mode for the ModelFormSet which will fix this issue.

comment:9 Changed 22 months ago by Parth Patil

Here is a link to the PR for this ticket, please have a look

comment:10 Changed 22 months ago by Mariusz Felisiak

Has patch: set

comment:11 Changed 22 months ago by Mariusz Felisiak

Needs documentation: set
Patch needs improvement: set
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