How to create a ModelViewset when model has OneToOneField? - django

Question

The idea is to have a model like this:
class Object(models.Model):
user = models.OneToOneField(User, on_delete=models.CASCADE)
name = models.CharField(max_length=256)
def __str__(self):
return self.name
and then create a serializer and a ModelViewSet related to it.
The problem is that ModelViewSet must return a queryset but I want to work with single objects due to the one-to-one relation.
How should I proceed?

Answer 1

As mentioned in the documentation:
The ModelViewSet class inherits from GenericAPIView and includes implementations for various actions, by mixing in the behavior of the various mixin classes.
This means that ModelViewSet also takes care of situation where a specific Object should be returned. You can even override def get_object(self) if you want a behavior more complex than what is implemented (see this SO question).
However, to really ensure that only one Object is returned, I would advice you to use a field as a unique primary key. You would populate this field on insertion (manually or automatically) and then use it as a lookup_field.
Below, I assumed that you already had a __str__(self) function in your User model as well.
Then, your Object model would become:
class Object(models.Model):
id = models.BigAutoField(primary_key=True) # or another unique primary_key field
user = models.OneToOneField(User, on_delete=models.CASCADE)
name = models.CharField(max_length=256)
def __str__(self):
return f"{self.name} ({self.id})"
Your serializer would be:
class ObjectSerializer(serializers.ModelSerializer):
class Meta:
model = Object
fields = ("id", "name", "user")
id = serializers.CharField(required=True)
Your ModelViewSet would be something like:
class ObjectViewSet(viewsets.ModelViewSet):
http_method_names = ["get"]
# parser_classes = [JSONParser] # Replace with your parser class
queryset = Object.objects.all()
serializer_class = ObjectSerializer
lookup_field = "id"
Finally, to make the whole thing works you would also have to register your ModelViewSet in your urlpatterns.
I use to explicitly bind my ViewSet classes into a set of concrete views but this is more of a personal choice so it's up to you. You can check the corresponding documentation for more info.
urlpatterns = [
...
path(
r"objects/<str:id>",
ObjectViewSet.as_view({"get": "retrieve"}),
),
...
]
With all this, a request to <BASE_URL>/objects/<YOUR_OBJECT_ID> should return only one Object result.