Original exception text was: 'QuerySet' object has no attribute 'weight'

Question

I got an Exception Got AttributeError when attempting to get a value for field weight on serializer WeightHistorySerializer. The serializer field might be named incorrectly and not match any attribute or key on the QuerySet instance. Original exception text was: 'QuerySet' object has no attribute 'weight'. When I tried to retrive data.

models.py

class WeightHistory(models.Model):
    user = models.ForeignKey(User, on_delete=models.CASCADE)
    weight = models.FloatField(null=False, blank=False)
    created_at = models.DateTimeField(auto_now_add=True)

serializers.py

class WeightHistorySerializer(serializers. HyperlinkedModelSerializer):
    class Meta:        
        model = WeightHistory        
        fields = (
            'id', 
            'weight',
            'user_id',
            'created_at'
        )   
        read_only_fields = ('id',)

views.py

def weight_history_detail(request, user_id):
    # Retrieve, update or delete a weight_history/detail.
    try:
        weight_history = WeightHistory.objects.filter(user_id=user_id)
    except WeightHistory.DoesNotExist:
        return Response(status=status.HTTP_404_NOT_FOUND)

    if request.method == 'GET':
        serializer = WeightHistorySerializer(weight_history)
        return Response(serializer.data)

If it change to

weight_history = WeightHistory.objects.get(user_id=user_id)

It returns only one row, But I want all the rows with given user_id. So, What should I do to get all list with given user_id.

Answer 1

'QuerySet' object has no attribute 'weight'.

Yes. QuerySet is a Set, a list of objects.

<QuerySet [<Object1>, <Object2>,..]>

And that list has no attribute weight. Instead, the objects inside the QuerySet has the attribute weight.

weight_history = WeightHistory.objects.filter(user_id=user_id)

filter returns a QuerySet, a list of WeightHistory objects with user_id=user_id.

And you are trying to serialize the list as a single object.

Instead of this:

serializer = WeightHistorySerializer(weight_history)

Do this:

serializer = WeightHistorySerializer(weight_history, many=True)

many=True tells the serializer that a list of objects being passed for serialization.

Moreover,

try:
   weight_history = WeightHistory.objects.filter(user_id=user_id)
except WeightHistory.DoesNotExist:
   return Response(status=status.HTTP_404_NOT_FOUND)

This doesn't throw an exception at all. filter returns an empty QuerySet if no objects exist. <QuerySet []>.

So the final code is:

def weight_history_detail(request, user_id):
    # Retrieve, update or delete a weight_history/detail.
    weight_history = WeightHistory.objects.filter(user_id=user_id)
    if weight_history.count()<1:
        return Response(status=status.HTTP_404_NOT_FOUND)

    if request.method == 'GET':
        serializer = WeightHistorySerializer(weight_history, many=True)
        return Response(serializer.data)