两表多对多关联时，append 失效

[ppd324]

type UserTag struct {
	gorm.Model
	TagName  string       `gorm:"type:varchar(50);unique;comment:'标签名'"`
	Category string       `gorm:"type:varchar(50);default:null;comment:标签类别"`
	Describe string       `gorm:"type:varchar(100);comment:'标签描述'"`
	Users    []*UserInfos `gorm:"many2many:users_to_tags;"`
}

type User struct {
        Id  int
        PayedUser            int        `gorm:"type:int(11);default:0;comment:'付费用户标识'" json:"payed_user"`
	InvitationCode       string     `gorm:"type:varchar(20)"`
	InvitationNum        int        `gorm:"type:int(11);default:0"`
	Tags                 []*UserTag `gorm:"many2many:users_to_tags;"`
}


err = demoMysqlDB.Debug().Model(&UserInfos{Id: 5,}).Association("Tags").
         Append(&UserTag{
                       TagName: "测试"，
          })

当我想给用户添加标签是，该标签数据库已经在存在，添加不生效，关联表中用户id关联到了0

[github-actions]

The issue has been automatically marked as stale as it missing playground pull request link, which is important to help others understand your issue effectively and make sure the issue hasn't been fixed on latest master, checkout https://github.com/go-gorm/playground for details. it will be closed in 30 days if no further activity occurs. if you are asking question, please use the Question template, most likely your question already answered https://github.com/go-gorm/gorm/issues or described in the document https://gorm.io ✨ Search Before Asking ✨