Django Rest Framework ModelSerializer保存錯誤

Question

我想從傳遞給序列化程序的數據中添加一個額外的鍵值對，但是會發生以下錯誤：

ValueError: Cannot assign "1": "ExamLog.student" must be a "Students" instance.

serializers.py

class ExamSubmitSerializer(serializers.ModelSerializer):
    def to_internal_value(self, data):
        x = get_score(data['exam']) # This will result to 1, I have no errors with this one
        data['score'] = x 
        return data

    class Meta:
        model = ExamLog
        fields = ('student', 'score', 'exam_started')

    # Will use this one for auto-email and auto-pdf creation
    # def create(self, validated_data):
    #   # print "-----"
    #   # y = validated_data.pop('exam', None)
    #   # print y
    #   print validated_data
        # x = self.Meta.model(**validated_data)
        # x.save()

views.py

@api_view(['POST'])
def submitExam(request):
    if request.method == 'POST':
        data = request.data
        student = data.get('student', None)
        exam = data.get('exam', None)
        serializer = ExamSubmitSerializer(data=data)
        if serializer.is_valid():
            serializer.save()
            return Response(standardResponse(data=serializer.data), status=status.HTTP_201_CREATED)
        else:
            return Response(standardResponse(errors=serializer.errors), status=status.HTTP_400_BAD_REQUEST)

urls.py

urlpatterns = [
  # url(r'^view/', views.viewExams),
  url(r'^view/', views.getQuestion),
  url(r'^add/', views.addUpdateQuestion),
  url(r'^submit/', views.submitExam),
  url(r'^', views.filterQuestions),
]

models.py

class Choices(models.Model):
    question = models.ForeignKey(Questions)
    choice = models.TextField()
    correct = models.NullBooleanField()

    def __unicode__(self):
        return self.choice

class ExamLog(models.Model):
    student = models.ForeignKey(Students)
    # answers = models.JSONField? # To be used for data science statistical purposes
    score = models.PositiveIntegerField(null=True, blank=True, default=None)
    exam_started = models.DateTimeField(null=True, blank=True, default=None)
    exam_finished = models.DateTimeField(auto_now_add=True)

get_score方法：

def get_score(answers):
    x  = Choices.objects.filter(id__in=answers).filter(correct=1)
    return x.count()

API請求示例：

{"student":1, "exam":[ 1597, 1620, 1906, 1648, 1656, 1718, 1611, 1551, 1812, 1745, 1489, 1815, 1527, 1485, 1512, 1831, 1545, 1713, 1808, 1530 ]}

我理解錯誤的含義。 應該傳遞模型的實例而不是它的id，但是當我不包含to_internal_value（）方法時，不會發生此錯誤並實際保存。 但是，這將導致得分為空

我想在分數上添加一個值，該值將來自數據的檢查鍵

Answer 1

def to_internal_value(self, data):
    x = get_score(data['exam']) # This will result to 1, I have no errors with this one
    data['score'] = x

    data = super(ExamSubmitSerializer, self).to_internal_value(data)

    return data

在返回數據之前調用方法超級將允許再次清理數據以及操縱的得分數據鍵值。