Django - grabbing an additional field from related table - django

Question

I have the following models:
class User(AbstractBaseUser, PermissionsMixin):
SUPERVISOR = 1
REVIEWER = 2
VERIFIER = 3
READ_ONLY = 4
USER_TYPE = [
(SUPERVISOR, 'Supervisor'),
(REVIEWER, 'Reviewer'),
(VERIFIER, 'Verifier'),
(READ_ONLY, 'Read Only'),
]
email = models.EmailField(max_length=50, unique=True)
name = models.CharField(max_length=100)
phone = models.CharField(max_length=50, null=True)
role = models.IntegerField(
choices=USER_TYPE,
default=READ_ONLY
)
is_active = models.BooleanField(default=True)
class Comment(models.Model):
text = models.TextField()
user = models.ForeignKey(
settings.AUTH_USER_MODEL,
on_delete=models.PROTECT
)
View:
class CommentViewSet(BaseCertViewSet):
queryset = Comment.objects.all()
serializer_class = serializers.CommentSerializer
Serializer:
class CommentSerializer(serializers.ModelSerializer):
user = serializers.SlugRelatedField(
read_only=True,
slug_field='name'
)
class Meta:
model = Comment
fields = ('id', 'text', 'user',)
read_only_fields = ('id',)
My question: when I hit the comment API endpoint, I'd like it to return the user role from the user model as well. How do I go about doing that?

Answer 1

I believe you can use a QuerySet.annotation:
EDIT: F is from django.db.models so you have to import that as well.
queryset = Comment.objects.annotate(user_role=F("user__role")) in your CommentViewSet
EDIT:
In order to get the serializer to recognize the field that you are trying to add to the QuerySet, you must also define the field on the serializer like this:
class CommentSerializer(serializers.ModelSerializer):
user = serializers.SlugRelatedField(
read_only=True,
slug_field='name'
)
# add line below to your code
user_role = IntegerField()
class Meta:
model = Comment
# you have to add it to the list of fields as well
fields = ('id', 'text', 'user', 'user_role')
read_only_fields = ('id',)

Answer 2

The solution that worked for me (not sure it's the most elegant one, happy to change to a better way of doing that):
class CommentSerializer(serializers.ModelSerializer):
"""Serializer for Comment object"""
user = serializers.SlugRelatedField(
read_only=True,
slug_field='name'
)
role = serializers.SerializerMethodField()
def get_role(self, obj):
user = obj.user_id
role = User.objects.only('id').get(
id=user).role
return role
class Meta:
model = Comment
fields = ('id', 'value', 'text', 'user', 'role',
'date_created', 'date_updated')
read_only_fields = ('id',)