On my generic class based CreateView, I would like to perform an instruction which creates new objects from another model related to the current created object.
Example:
Collection
is a model which is related to 3 differentsElement
objects. When I create aMyCollection
object, which is related to aCollection
and aUser
, 3MyElement
object must be created too and related to the newly createdMyCollection
object. One for eachElement
related toCollection
.
# models.py from django.contrib.auth.models import User from django.db import models class Collection(models.Model): # attributes and methods... class Element(models.Model): collection = models.ForeignKey(Collection, # more arguments...) # more attributes and methods class MyCollection(models.Model): user = models.ForeignKey(User, # more arguments...) collection = = models.ForeignKey(Collection, # more arguments...) # more attributes and methods def get_absolute_url(self): reverse(# some url with the object pk) class MyElement(models.Model): element = models.ForeignKey(Element, # more arguments...) my_collection = models.ForeignKey(MyCollection, # more arguments...) # more attributes and methods
I’m using the generic CreateView from Django and after a little bit of research, I saw that it was possible to perform additional actions in the CreateView by overriding the get_success_url() method.
In my example, I did something similar:
# views.py from django.views.generic import CreateView from .utils import create_myelements_for_mycollection class MyCollectionCreateView(CreateView): model = MyCollection # more attributes and methods... def get_success_url(self): create_myelements_for_mycollection(self.get_object()) # Here is where the bug occurs, works fine without this line return super().get_success_url()
# utils.py from .models import Collection, Element, MyCollection, MyElement def create_myelements_for_mycollection(my_collection): for element in my_collection.collection.elements_set.all(): MyElement.objects.create( element=element, my_collection=my_collection, )
# urls.py from django.urls import re_path from . import views urlpatterns = [ re_path( r"^myelement/l/$", views.MyElementListView.as_view(), ), re_path( r"^myelement/r/(?P<pk>[0-9]+)/$", views.MyElementDetailView.as_view(), ), re_path( r"^myelement/c/(?P<element_pk>d+)/$", views.MyElementCreateView.as_view(), ), re_path( r"^mycollection/l/$", views.MyCollectionListView.as_view(), ), re_path( r"^mycollection/r/(?P<pk>[0-9]+)/$", views.MyCollectionDetailView.as_view(), ), re_path( r"^mycollection/c/(?P<collection_pk>d+)/$", views.MyCollectionCreateView.as_view(), ), ]
When I create a new MyCollection
object, all the MyElements
are successfully created in the database but I got this error:
AttributeError: Generic detail view MyCollectionCreateView must be called with either an object pk or a slug in the URLconf.
I don’t understand why.
My CreateView url doesn’t have any pk because when you create a new object, it doesn’t have a pk yet. Also, MyCollection
has it’s own get_absolute_url
. Without that specific instruction, I works fine.
Can someone explain me what causes the error and if there is a better way to perform an instruction like this after the object creation ?
Thank you for your help.
FYI: Django 3.1 Pyhton 3.8
EDIT
I tried to use a post_save signal instead (which is actually way cleaner to write), but I’m stuck with exactly the same error.
# models.py from django.db.models.signals import post_save from django.dispatch import receiver from .utils import create_myelements_for_mycollection # ...models @receiver(post_save, sender=MyCollection) def create_myelements_for_mycollection(sender, instance, **kwargs): if instance is created: # ? (Didn't look at how to write this condition in a signal yet) create_myelements_for_mycollection(my_collection)
AttributeError: Generic detail view MyCollectionCreateView must be called with either an object pk or a slug in the URLconf.
EDIT 2
By removing the get_absolute_url()
override from the MyCollectionCreateView
class, it actually works. It’s great but I would still like to know what the issue was. Probably something stupid I didn’t see, if this solved the issue.
# models.py # ... previous code class MyCollectionCreateView(CreateView): model = MyCollection # more attributes and methods... # Removing this solved the issue # def get_success_url(self): # create_myelements_for_mycollection(self.get_object()) # # return super().get_success_url() # more code ...
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Answer
get_absolute_url()
is used when a new instance is made for a model, as django must know where to go when a new post is created or a new instance is created.
From the error
AttributeError: Generic detail view MyCollectionCreateView must be called with either an object pk or a slug in the URLconf.
It tells you that it must be called with an object pk
or a slug
, as such your construction of the URL is where the problem lies. I am not sure if the method create_myelements_for_mycollection()
caters that need.
Ideally what you need is something like, e.g.
def get_absolute_url(self): return f"/mycollection/{self.slug}/"
to generate the URL
in the above pattern to be used for example in an anchor tag.