Limit number of model instances to be created - django

Question

I have model from which I only want to create one instance, and no more instances should be allowed.

Is this possible? I\'ve got a feeling that I\'ve seen this done

Answer 1

If you just want to prevent users using the administrative interface from creating extra model objects you could modify the "has_add_permission" method of the model's ModelAdmin class:

# admin.py
from django.contrib import admin
from example.models import Example

class ExampleAdmin(admin.ModelAdmin):
  def has_add_permission(self, request):
    num_objects = self.model.objects.count()
    if num_objects >= 1:
      return False
    else:
      return True

admin.site.register(Example, ExampleAdmin)

This will remove the "add" button in the administrative interface preventing users from even attempting to create more than the specified number (in this case 1). Of course programatic additions will still be possible.