DRF IntegrityError: NOT NULL constraint failed: user_id

Question

I can't figure out how to pass user object to the following serializer:

class ReviewSerializer(serializers.ModelSerializer):
    user = UserSerializer(read_only=True)

    class Meta:
        model = Review
        fields = ('pk', 'title', 'user', 'movie', 'timestamp', 'review_text',)

I have this viewset:

class ReviewsViewSet(viewsets.ModelViewSet):
    queryset = Review.objects.all()
    serializer_class = ReviewSerializer

and this model:

class Review(models.Model):
    title = models.CharField(max_length=255)
    user = models.ForeignKey(User, on_delete=models.CASCADE, related_name='reviews')
    movie = models.ForeignKey(Movie, on_delete=models.CASCADE, related_name='reviews')
    review_text = models.TextField()
    timestamp = models.DateTimeField(auto_now_add=True)

    def __str__(self):
        return '{movie} review by {user}'.format(user=self.user, movie=self.movie)

My javascript request looks like this:

return axios({
  method: 'post',
  url: 'http://localhost:8000/api/reviews/',
  data: { // Using data from Vue
    title: this.review_title,
    movie: this.id,
    review_text: this.review_text,
    user: JSON.stringify(this.user)
  },
  headers: {
    'Content-Type': 'application/json',
    Authorization: `JWT ${token}`
  }
})

It gives me this traceback.

How should I pass the user object to the request?

Thanks in advance.

Animated

Answer 1

Remove read_only=True from serializer

class ReviewSerializer(serializers.ModelSerializer):
    user = UserSerializer()

    class Meta:
        model = Review
        fields = ('pk', 'title', 'user', 'movie', 'timestamp', 'review_text',)

If you set read_only=True, the DRF will not takes the value from input source even if it's there

From the doc,

Read-only fields are included in the API output, but should not be included in the input during create or update operations. Any 'read_only' fields that are incorrectly included in the serializer input will be ignored.

Set this to True to ensure that the field is used when serializing a representation, but is not used when creating or updating an instance during deserialization.

Defaults to False

UPDATE
You should override the create() method of ReviewSerializer as

class ReviewSerializer(serializers.ModelSerializer):
    user = UserSerializer()

    def create(self, validated_data):
        user_dict = validated_data.pop('user')
        user_obj, created = User.objects.get_or_create(**user_dict)
        return Review.objects.create(user=user_obj, **validated_data)

    class Meta:
        model = Review
        fields = ('pk', 'title', 'user', 'movie', 'timestamp', 'review_text',)

for debug purpose only

class ReviewsViewSet(viewsets.ModelViewSet):
    queryset = Review.objects.all()
    serializer_class = ReviewSerializer

    def create(self, request, *args, **kwargs):
        print(request.data)  # print here <<<<
        return super(ReviewsViewSet, self).create(request, *args, **kwargs)

Copilot

Yes, but If I take out read_only=True it gives me: "A user with that username already exists.". So, I don't want to post a new user, just to take the user data needed to create that particular review. – Animated

Can you add the value of user that you're passing from front-end? – Copilot

@Animated Anyway I've updated the answer. Hope it helps – Copilot

I pass the whole user object that I stored in Vuex so I can display user details and stuff. So it looks like this "{"pk":1,"username":"test","first_name":"test","last_name":"test","email":"[email protected]"}". I sent a request with all of the fields required, especially user field, and returns another error: "user": [ "This field is required." ]. – Animated

Yes, I edited the serializer according to your answer. – Animated

The error says that the user data not reaching to DRF view – Copilot

@Animated print the data in DRF view and add it here, (check the updated answe) – Copilot

It does not reach create() method. I tried your updated answer, it displays nothing, only Bad request and the status code. Note: I tried to display some random string, to see if it displays anything at all. – Animated

create method of view or serializer? – Copilot

Oh, sorry, It was for the viewset, since it has request, my bad. Here: <QueryDict: {'review_text': ['something'], 'title': ['Something'], 'user': ['{"pk":1,"username":"test","first_name":"test","last_name":"test","email":"[email protected]"}'], 'movie': ['8']}> – Animated

Can you add the result of print(type(request.data['user'])) in create() method of view ? – Copilot

<class 'str'> is the output – Animated

Then, Change user: JSON.stringify(this.user) to user: this.user in your JS code – Copilot

Oh, ok, now it's working. Thank you for detalied answer, I learned a bit how to debug DRF now. – Animated

Answer 2

just add this

class ReviewSerializer(serializers.ModelSerializer):
    user = UserSerializer(read_only=True)
    # new line
    user_id = serializers.IntegerField(write_only=True)

    class Meta:
        model = Review
        fields = (
            'pk', 'title', 'user', 'movie', 'timestamp', 'review_text',
            'user_id', # new field
        )

read_only

Read-only fields are included in the API output, but should not be included in the input during create or update operations. Any 'read_only' fields that are incorrectly included in the serializer input will be ignored.

Set this to True to ensure that the field is used when serializing a representation, but is not used when creating or updating an instance during deserialization.

Defaults to False

write_only

Set this to True to ensure that the field may be used when updating or creating an instance, but is not included when serializing the representation.

Defaults to False

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