Django Rest Framework POST 失败：“cat_id”列中的空值违反了非空约束

Question

I've recently converted my views to generic class-based views, however I've just noticed that POST requests fail on classes that have foreign-keys. The following is my code, followed by the error message.

models.py

class Category(models.Model):
    name = models.CharField(max_length=25, blank=False)

    class Meta:
        ordering = ('id',)


class Task(models.Model):
    name = models.CharField(max_length=25, blank=False)
    cat = models.ForeignKey(Category, on_delete=models.CASCADE)

    class Meta:
        ordering = ('id',)

serializers.py

class TaskSerializer(serializers.ModelSerializer):
    class Meta:
        model = Task
        fields = ('id', 'name', 'cat_id')


class CategorySerializer(serializers.ModelSerializer):
    class Meta:
        model = Category
        fields = ('id', 'name')

views.py

class TaskList(generics.ListCreateAPIView):
    """
    List all Tasks (OR for specified cat_id)
    """
    queryset = Task.objects.all()
    serializer_class = TaskSerializer
    filter_fields = ('cat_id',)

urls.py

path('tasks/', views.TaskList.as_view()),

Error returned

django.db.utils.IntegrityError: null value in column "cat_id" violates not-null constraint
DETAIL:  Failing row contains (51, buy-some, null).

REQUEST content: JSON Object

{
    "name": "buy-some",
    "cat_id": 1
}

Additionally, Content-Type, Accept headers are set to application/json .

Category with id=1 exists

Answer 1

Probably what you want is to define the field cat in your TaskSerializer to be a PrimaryKeyRelatedField (documentation here) , in your case would be:

class TaskSerializer(serializers.ModelSerializer):
    cat = PrimaryKeyRelatedField(queryset=Category.objects.all())
    class Meta:
        model = Task
        fields = ('id', 'name', 'cat')

Then in your request just send the pk in the "cat" field like so:

{
    "name": "buy-some",
    "cat": 1
}

This should do the trick.