CODEWITHSUNDEEP
django
Pikaling
Pikaling

Reputation: 8312

Stop a M2M relationship being saved in django

I have an AdminModel that allows users to save with any of the fields left empty. However, I don't want them to be able to save when all fields are empty. I've implemented this using the following:

def save_model(self, request, obj, form, change):
    if form.has_changed():
        obj.save()
    else:
        pass

However, the Model has a M2M relationship with another Model, so I get the following error when I hit save:

instance needs to have a primary key value before a many-to-many relationship can be used.

What do I need to add to this method to stop it trying to create the M2M relationship?

Edit:

I've added hacky workaround, but I'd be interested in knowing if there's a better way of doing it. The workaround was to change the else so it changes the ModelAdmin's field attribute so that it doesn't contain the field for the M2M relationship - this prevents it from trying to make the relationship. This is not only hacky, but also only works after it's failed to save the model once and thrown an error...

Upvotes: 0

Views: 255

Answers (2)

Timmy O'Mahony
Timmy O'Mahony

Reputation: 53999

It would be best to do the validation at the form level instead of the admin level. To do this, create a custom Form class to be used by your ModelAdmin. So create a forms.py:

from myapp.models import MyModel
from django import forms

class MyModelForm(forms.ModelForm):
    pass

    class Meta:
        model = MyModel

    def clean(self):
        empty = True
        for field_name, field_data in self.cleaned_data.iteritems():
            if field_data:
                empty = False
        if empty:
            raise forms.ValidationError("The form cannot be empty")
        return self.cleaned_data

and allow your admin to use this form. In admin.py:

from myapp.forms import MyModelForm
from django.contrib import admin

class MyModelAdmin(admin.ModelAdmin):
    ...
    form = MyModelForm

Upvotes: 2

Yuji 'Tomita' Tomita
Yuji 'Tomita' Tomita

Reputation: 118488

You can't - save_m2m is called after save_model. The docs specifically say this hook is not for veto purposes.

ModelAdmin.save_model() and ModelAdmin.delete_model() must save/delete the object, they are not for veto purposes, rather they allow you to perform extra operations.

What you need is form validation to prevent save_model from triggering. Somehow, you need to detect when all fields are left blank. 

class MyForm(forms.ModelForm):
    class Meta:
        model = MyModel

    def clean(self):
        if not any(self.cleaned_data.values()):
            raise forms.ValidationError("All fields cannot be blank!")
        return self.cleaned_data

class MyAdmin(admin.ModelAdmin):
    form = MyForm

Upvotes: 3

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