Create a field with conditions - django

Question

I'm a beginner in django rest framework.
I am wondring if there is a way to create a field from a GET. For example if "count" == 0, create a field named "available" : "out_of_stock" else "available
models.py
class Count(models.Model):
name = models.CharField(max_length=100)
count = models.IntergerField()
serializers.py
class CountSerializer(serializers.ModelSerializer):
class Meta:
model = Count
fields = '__all__'
views.py
class CountViewSet(viewsets.ModelViewSet):
queryset = Count.objects.all()
serializer_class = CountSerializer
output
[
{
"id": 1,
"count": 10,
},
{
"id": 2,
"count": 0,
}
]

Answer 1

First, for a good practise, avoid using fields = '__all__' and instead define your fields specifically.
For ex: fields = ['name', 'count'], you will see doing so will pay off shortly as I continue.
DRF has the feature to mark a serializer field as read_only or write_only so it works on specific requests, as it looks from the naming read_only intended for GET and write_only for POST.
You can do what you are looking for in so many ways, but I think the easiest way to do it would be using SerializerMethodField like this:
class CountSerializer(serializers.ModelSerializer):
available = serializers.SerializerMethodField()
def get_available((self, obj):
value = 'out_of_stock' if obj.count == 0 else 'available'
return value
class Meta:
model = Count
fields = ['name', 'count', 'available']
For more advanced needs, you can read about dynamic serializer fields on drf docs, see.