如何验证DRF中的更新字段？

Question

我有一个带有外键的模型的序列化器.要求是在创建时,可以将外键设置为相关模型中的任何现有对象,但是在更新时,不能更改相关对象.我可以在自定义中检查这个update(),但是使用序列化验证来检查这个会更优雅吗？但我不确定如何.示例代码:

class Person(models.Model):
    name = models.CharField(max_length=256)
    spouse = models.ForeignKey(Person)

class PersonSerializer(serializers.ModelSerializer):
    class Meta:
        model = Person

    # this is how I know how to do this
    def create(self, validated_data):
        try:
            spouse = Person.objects.get(pk=int(validated_data.pop('spouse')))
        except Person.DoesNotExist:
            raise ValidationError('Imaginary spouses not allowed!')
        return Person.objects.create(spouse=spouse, **validation_data)

    def update(self, person, validated_data):
        if person.spouse.pk != int(validated_data['spouse']):
            raise ValidationError('Till death do us part!')
        person.name = validation_data.get('name', person.name)
        person.save()
        return person

   # the way I want to do this
   def validate_spouse(self, value):
       # do validation magic

Answer 1

您绝对可以使用字段上的验证来执行此操作.您检查是否是更新与创建的方式是self.instance在验证功能中检查.在序列化程序文档中有一点提到它.

self.instance 将保存现有对象及其值,以便您可以使用它进行比较.

我相信这应该适用于您的目的:

def validate_spouse(self, value):
    if self.instance and value != self.instance.spouse:
        raise serializers.ValidationError("Till death do us part!")
    return value

另一种方法是,如果您正在更新,则覆盖字段是read_only.这可以__init__在序列化器中完成.与验证器类似,您只需查找实例以及是否有数据:

def __init__(self, *args, **kwargs):
    # Check if we're updating.
    updating = "instance" in kwargs and "data" in kwargs

    # Make sure the original initialization is done first.
    super().__init__(*args, **kwargs)

    # If we're updating, make the spouse field read only.
    if updating:
        self.fields['spouse'].read_only = True