python - Django REST 框架 : how to substitute null with empty string?

Question

我有一个 ImageField 类型如下的模型:

class Attendance(models.Model):
    face_image = models.ImageField(, blank=True, null=True, storage=MediaStorage())

基于模型的序列化器

class AttendanceSerializer(serializers.ModelSerializer):

    class Meta:
        model = Attendance
        fields = ('id','face_image')

但是，如果图像字段为空，则显示如下

Its now showing like this in the json

  {
    "id": 1,
    "face_image": null
  }

如果 face_image (ImageField) 为 None，它将显示为 null 的输出。我想要的是将 null 替换为像这样的空字符串 ""

Answer 1

重写 AttendanceSerializer 的 to_representation() 方法，

class AttendanceSerializer(serializers.ModelSerializer):
    class Meta:
        model = Attendance
        fields = ('id', 'face_image')

    <b>def to_representation(self, instance):
        data = super().to_representation(instance)
        if not data['face_image']:
            data['face_image'] = ""
        return data</b>

---

更新(11/03/2019)

I have lots of fields and its not really good idea that I repeat this code for all of them, isn't there a better way to do it for all fields?

class AttendanceSerializer(serializers.ModelSerializer):
    class Meta:
        model = Attendance
        fields = ('id', 'face_image')

    def to_representation(self, instance):
        <b>my_fields = {'field_1', 'field_2', 'field_3', 'field_4', 'field_5'}</b>
        data = super().to_representation(instance)
        <b>for field in my_fields:
            try:
                if not data[field]:
                    data[field] = ""
            except KeyError:
                pass</b>
        return data