django rest framework : <Objectname: Objectname object> is not JSON serializable

Question

I have a customer model and an event model. event model refer to the customer. A customer has many events. My requirement is when I get the customer, I need the latest event object of the customer. When I call the customer Get API, it shows the following error,

TypeError at /api/v1/customer

is not JSON serializable

My Models

class Customer(models.Model):
    id = models.UUIDField(primary_key=True, default=uuid.uuid4, editable=False)
    name = models.CharField(max_length=20, unique=True)
    #some more fields to go
    def __str__(self):
        return str(self.name)


    def latest_event_name(self):
        """Return latest event """

        latest_event = self.customer_events.order_by('-event_date').last()
        return latest_event if latest_event else None



class Event(models.Model):
    id = models.UUIDField(primary_key=True, default=uuid.uuid4, editable=False)
    event_name = models.CharField(max_length=200, unique=True)

    customer = models.ForeignKey(customer_models.Customer, db_index=True, on_delete=models.SET_NULL,
                                 related_name='customer_events', null=True)
   #some more fields to go

serializer

class CustomerSerializer(serializers.ModelSerializer):
    latest_event_name = serializers.ReadOnlyField()

    class Meta:
        model = Customer
        fields = '__all__'

List the rest of the fields in Event - clearly one of them is preventing serialization. — arvindch
– arvindch, Commented Mar 7, 2017 at 7:48
Where are you trying to do the serialzing? If you get a CustomerEvent instance, what is it supposed to serialize into? — Sayse
– Sayse, Commented Mar 7, 2017 at 7:52
@shadow - Its the latest_event_name that isn't serializable since DRF has no idea how to serialize the queryset result — Sayse
– Sayse, Commented Mar 7, 2017 at 7:52
does latest_event_name = EventSerializer(read_only=True) do what you're looking for? (You'll need to write the event serializer) — Sayse
– Sayse, Commented Mar 7, 2017 at 7:58
If I use code return latest_event.event_name if latest_event else None in model,` 'latest_event_name = serializers.ReadOnlyField()' ` will work in serializer. It will return the event name. But I need the full event object. — Arun SS
– Arun SS, Commented Mar 7, 2017 at 9:46

PROW · Accepted Answer · 2017-03-07 08:34:02Z

2

As you are using Events in

def latest_event_name(self): ...

you'll have to create a serializer for the Event model, because that method returns an instance of the model Event.

I think that, if you just return the id of the Event as a str, you will not have that problem, so you wouldn't have to create a seralizer for the Event model.

answered Mar 7, 2017 at 8:34

PROW

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1 Comment

Arun SS Over a year ago

I need the full event object

Arun SS · Accepted Answer · 2017-03-07 10:25:50Z

0

Anyway now fixed the issue by the following method.

def latest_event(self):
latest_event = self.customer_events.order_by('-event_date').last()
eventDict = None
if latest_event:
    eventDict = {"event_id": latest_event.id, "event_name": latest_event.event_name}
return eventDict

Not sure whether its the correct method or not.

answered Mar 7, 2017 at 10:25

Arun SS

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1 Comment

PROW Over a year ago

Of course you can do that, basically you are serializing the object by hand

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