from rest_framework.validators import UniqueValidator
slug = SlugField(
  max_length=100,
  validators=[UniqueValidator(queryset=BlogPost.objects.all())]
)

from rest_framework.validators import UniqueTogetherValidator

class ExampleSerializer(serializers.Serializer):
  class Meta:
    validators = [
      UniqueTogetherValidator(
        queryset=ToDoItem.objects.all(),
        fields=('list', 'position')
      )
    ]

	# 所有字段。attrs是字段验证合法之后返回的总的dict
  def validate(self, attrs):
    #前端没有传mobile值到后端，这里添加进来
    attrs["mobile"] = attrs["username"]
    #code是自己添加得，数据库中并没有这个字段，验证完就删除掉
    del attrs["code"]
    return attrs

class MobileVerifySerializer(serializers.ModelSerializer):

  #CareerUser中没有code字段，这里需要自定义一个code序列化字段
  code = serializers.CharField(required=True, write_only=True, max_length=4, min_length=4,
                 error_messages={
                    "blank": "请输入验证码",
                    "required": "请输入验证码",
                    "max_length": "验证码格式错误",
                    "min_length": "验证码格式错误"
                 },
                help_text="验证码")
  #验证用户名是否存在
  username = serializers.CharField(label="用户名", help_text="用户名", required=True, allow_blank=False,
                   validators=[UniqueValidator(queryset=CareerUser.objects.all(), message="用户已经存在")])

  #验证code
  def validate_code(self, code):
    # 用户注册，已post方式提交注册信息，post的数据都保存在initial_data里面
    #username就是用户注册的手机号，验证码按添加时间倒序排序，为了后面验证过期，错误等
    verify_records = VerifyCode.objects.filter(mobile=self.initial_data["username"]).order_by("-add_time")

    if verify_records:
      # 最近的一个验证码
      last_record = verify_records[0]
      # 有效期为五分钟。
      five_mintes_ago = datetime.now() - timedelta(hours=0, minutes=5, seconds=0)
      if five_mintes_ago > last_record.add_time:
        raise serializers.ValidationError("验证码过期")

      if last_record.code != code:
        raise serializers.ValidationError("验证码错误")

    else:
      raise serializers.ValidationError("验证码错误")

def multiple_of_ten(value):
  if value % 10 != 0:
    raise serializers.ValidationError('Not a multiple of ten')

class GameRecord(serializers.Serializer):
  score = IntegerField(validators=[multiple_of_ten])
  ...