如何使用Django Rest Framework向用户添加汽车

Question

When i try to add a Car for my user this is what's happening

 "username": [
"A user with that username already exists."]

This is my models I'm using Django auth User model There are my models

class Car(models.Model): 
"""
CAR Table with a ForeingKey from USER Table

"""
user = models.ForeignKey(User, related_name='cars')
model = models.CharField(max_length=50)
color = models.CharField(max_length=20)
year = models.IntegerField()
seats = models.IntegerField()


def __unicode__(self):
    return u'%d: %s: %s: %d' % (self.id, self.model, self.color, self.year)

My Serializers

class CarSerializer(serializers.ModelSerializer):
class Meta:
    model = Car
    fields = (
        'model', 
        'color', 
        'seats'
        )      

class AddCarSerializer(serializers.ModelSerializer):
car = CarSerializer()
class Meta:
    model = User
    fields = (
        'username',
        'car'
        )

this is my View

class AddCarForUser(APIView):
authentication_classes = (TokenAuthentication,)
permission_classes = (IsAuthenticated,)

def put(self, request):
    car = AddCarSerializer(data = request.data)
    car.is_valid(raise_exception = True)
    car.save()
    return Response(status=status.HTTP_201_CREATED)

And this is what i'm sending in a Put Request

{
"username": "root",
"car": {
    "model": "Seat Ibiza",
    "color": "Verde",
    "seats": "4" 
}}

Answer 1

Your code doesn't works because you use serializer.ModelSerializer and the username attribute of the User class must be unique, that why It can't validate it. To overcome this, follow these steps.

1. Update your serializer AddCarSerializer . We add a custom field username to handle username passed without a unique, just a simple CharField . And we add create function because Nested Serializer can't handle creation or update out the box:

class AddCarSerializer(serializers.Serializer):
    # add username custom field
    username = serializers.CharField()
    car = CarSerializer()

    class Meta():
        fields = (
            'username',
            'car'
        )

    def create(self, validated_data):
        """ Add car to an user
        """
        tmp_car = validated_data.pop('car')
            user = User.objects.get(username=validated_data['username'])
        car = Car.objects.create(
            user=user,
            model=tmp_car['model'],
            color=tmp_car['color'],
            seats=tmp_car['seats'],
        )

        return car

2. update your view :

class AddCarForUser(APIView):

    def put(self, request):
        serializer = AddCarSerializer(data = request.data)
        if serializer.is_valid():
            serializer.save()
            return Response(status=status.HTTP_201_CREATED)
        return Response(status=status.HTTP_400_BAD_REQUEST)

3. update your Car model, because year attribute doesn't exist when we add a car to an user then, add null=True :

class Car(models.Model):
    user = models.ForeignKey(User, related_name='cars')
    model = models.CharField(max_length=50)
    color = models.CharField(max_length=20)
    year = models.IntegerField(null=True)
    seats = models.IntegerField()

And it should work. Don't forget to handle error like if the username passed doesn't exist.