相关代码如下：

type MainFields struct {
        Id int `orm:"auto"`
        Created time.Time `orm:"auto_now_add;type(datetime)"`
        Updated time.Time `orm:"auto_now;type(datetime)"`
    }

type Game struct {
    MainFields
    Players  []*Player `orm:"rel(m2m)"`
}

type Player struct {
    MainFields
    Games []*Game `orm:"reverse(many)"`
    NickName string
}

func insertTestData() {
    var playerA models.Player
    playerA.NickName = "CoolDude"
    id, err := models.ORM.Insert(&playerA)
    if err != nil {
        log.Printf(err.Error())
    } else {
        log.Printf("Player ID: %v", id)
    }

    var game models.Game
    id, err = models.ORM.Insert(&game)
    if err != nil {
        log.Printf(err.Error())
    } else {
        log.Printf("Game ID: %v", id)
    }

    m2m := o.QueryM2M(&game, "Players")
    num, err := m2m.Add(playerA)
    if err == nil {
        log.Printf("Added nums: %v", num)
    }
}

代码出自：
https://stackoverflow.com/questions/39770411/insert-for-model-with-m2m-in-beego-orm