Django Rest PUT请求序列化程序无法使用外键更新模型

Question

I have two models like following:

class Task(models.Model):
    user = models.ForeignKey(User, blank=True)
    what_task = models.CharField(max_length=100, )

    #This helps to print in admin interface
    def __str__(self):
        return u"%s" % (self.what_task)


class Step(models.Model):
    task = models.ForeignKey(Task, related_name='steps', on_delete=models.CASCADE, )
    what_step = models.CharField(max_length=50, blank=True, )

    #This helps to print in admin interface
    def __str__(self):
        return u"%s" % (self.what_step)

And I have written serializers:

class StepSerializer(serializers.ModelSerializer):
    class Meta:
        model = Step
        exclude = ('task',)

class TaskSerializer(serializers.ModelSerializer):
    steps = StepSerializer(many=True)
    class Meta:
        model = Task
        fields = '__all__'


    def create(self, validated_data):
        steps_data = validated_data.pop('steps')
        task = Task.objects.create(**validated_data)
        for step_data in steps_data:
            Step.objects.create(task=task, **step_data)
        return task 

    def update(self, instance, validated_data):
        steps_data = validated_data.pop('steps')

        instance.what_task = validated_data.get('what_task', instance.what_task)
        instance.how_often = validated_data.get('how_often', instance.how_often)
        instance.how_important = validated_data.get('how_important', instance.how_important)
        instance.why_perform = validated_data.get('why_perform', instance.why_perform)
        instance.why_important = validated_data.get('why_important', instance.why_important)
        instance.possible_improvement = validated_data.get('possible_improvement', instance.possible_improvement)
        instance.existing_solutions = validated_data.get('existing_solutions', instance.existing_solutions)
        instance.how_important_improvement = validated_data.get('how_important_improvement', instance.how_important_improvement)
        instance.advantages_of_improvement = validated_data.get('advantages_of_improvement', instance.advantages_of_improvement)

        instance.save()
        for step_data in steps_data:
            Step.objects.update(task=task, **step_data)
        return instance 

My view:

@api_view(['GET', 'POST'])
def task_list(request):
    """
    List all tasks, or create a new task.
    """
    if request.method == 'GET':
        print(request.user)
        tasks = Task.objects.filter(user=request.user.id)
        serializer = TaskSerializer(tasks, many=True)
        return Response(serializer.data)

    elif request.method == 'POST':
        serializer = TaskSerializer(data=request.data)
        print(request.data)
        if serializer.is_valid():
            serializer.save(user=request.user)
            return Response(serializer.data, status=status.HTTP_201_CREATED)
        else:
            return Response(
                serializer.errors, status=status.HTTP_400_BAD_REQUEST)


@api_view(['GET', 'PUT', 'DELETE'])
def task_detail(request, id):
    """
    Get, udpate, or delete a specific task
    """
    try:
        task = Task.objects.get(id=id)
    except Task.DoesNotExist:
        return Response(status=status.HTTP_404_NOT_FOUND)

    if request.method == 'GET':
        serializer = TaskSerializer(task)
        return Response(serializer.data)

    elif request.method == 'PUT':
        serializer = TaskSerializer(task, data=request.data)
        if serializer.is_valid():
            serializer.save(user=request.user)
            return Response(serializer.data)
        else:
            return Response(
                serializer.errors, status=status.HTTP_400_BAD_REQUEST)

    elif request.method == 'DELETE':
        task.delete()
        return Response(status=status.HTTP_204_NO_CONTENT)

My GET and POST requests works correct (first function in views), my tasks and associated steps are created in a single request however PUT request is wrong, I am not sure if I am updating the steps correctly; if I comment out from serializer the for loop, task is updated successfully.

What and how should I modify so that I can update a specific task with associated steps?

Answer 1

In your for loop, you update every existing task (inside update , you set the new values):

Step.objects.update(task=task, **step_data)

Instead, before the loop, you should delete all steps for that task and create the new steps:

...
    Step.objects.filter(task=instance).delete()
    for step_data in steps_data:
        Step.objects.create(task=instance, **step_data)
...

A more efficient approach would be to find all steps that do not exists (based on id) in validated_data and delete them, update the steps with an id, an create those without ids.