func TopicUrl(f1 validator.FieldLevel) bool {
    return true //返回true表示验证成功
}

func main(){
    router:=gin.Default()
    if v, ok := binding.Validator.Engine().(*validator.Validate); ok {  //类型断言
        v.RegisterValidation("topicurl", TopicUrl) //注册调用tag和自定义验证器
    }
    v1:=router.Group("/v1/topics")
    {
        v1.GET("/:topic_id",GetTopicDetail)
    }
}

type Topic struct {
    TopicID         int    `form:"id" json:"id"`
    TopicTitle      string `form:"title" json:"title" binding:"min=4,max=20"` //长度4到20之间
    TopicShortTitle string `form:"stitle" json:"stitle" binding:"required,nefield=ToipcTitle"`//required非空,nfield不能等于TopicTitle字段
    UserIP          string `form:"ip" json:"ip" binding:"ipv4"`
    TopicScore      int    `form:"score" json:"score" binding:"omitempty,gt=5"` //omitempty要么不传，传的话就要大于5
}

type Topic struct {
    TopicID         int    `form:"id" json:"id"`
    TopicTitle      string `form:"title" json:"title" binding:"min=4,max=20"`
    TopicShortTitle string `form:"stitle" json:"stitle" binding:"required,nefield=TopicTitle"`
    UserIP          string `form:"ip" json:"ip" binding:"ipv4"`
    TopicScore      int    `form:"score" json:"score" binding:"omitempty,gt=5"`
    TopicUrl        string `form:"url" json:"url" binding:"topicurl"` //绑定自定义的topicurl验证器
}

type Topics struct {
    TopicList [] *Topic `form:"topiclist" json:"topiclist" binding:"gt=0,lt=3,dive"` //dive表示进入列表或数组里面的字段去验证，这里是验证上面的Topic，dive要写在后面，不然如果lt写在dive后面就是验证里面的数据的lt>3，而不是列表的lt>3
    Size      int       `form:"size" json:"size"`
}