validate

在序列化器中需要同时对多个字段进行比较验证时，可以定义validate方法来验证，如

class BookInfoSerializer(serializers.Serializer):
    """图书数据序列化器"""
    id = serializers.IntegerField(label='ID', read_only=True)
    name = serializers.CharField(label='名称', max_length=20)
    pub_date = serializers.DateField(label='发布日期', required=False)
    readcount = serializers.IntegerField(label='阅读量', required=False)
    commentcount = serializers.IntegerField(label='评论量', required=False)

    def validate(self, attrs):
        readcount = attrs['readcount']
        commentcount = attrs['commentcount']
        if commentcount > readcount:
            raise serializers.ValidationError('评论量不能大于阅读量')
        return attrs

测试

>>> from book.serializers import BookInfoSerializer
>>> 
>>> data = {
...     'name':'Python高级',
...     'pub_date':'2020-01-01',
...     'readcount':100,
...     'commentcount':200
... }
>>> 
>>> serializer = BookInfoSerializer(data=data)
>>> 
>>> serializer.is_valid(raise_exception=True)
Traceback (most recent call last):
  File "<console>", line 1, in <module>
  File "/home/ubuntu/.virtualenvs/py3_django_2_2_5/lib/python3.6/site-packages/rest_framework/serializers.py", line 242, in is_valid
    raise ValidationError(self.errors)
rest_framework.exceptions.ValidationError: {'non_field_errors': [ErrorDetail(string='评论量不能大于阅读量', code='invalid')]}
>>>