Because it’s a HyperlinkedModelSerializer your serializer is trying to resolve the URL for the related User on your Bottle.
As you don’t have the user detail view it can’t do this. Hence the exception.
- Would not just registering the
UserViewSetwith the router solve your issue? - You could define the user field on your
BottleSerializerto explicitly use theUserSerializerrather than trying to resolve the URL. See the serializer docs on dealing with nested objects for that.