mgo自定义自增id

// id从1开始递增
func GenId(db *mgo.Database, forCName string) (int64, error) {
    IDInt64 := struct {
        Value int64 `bson:"max_id"`
    }{Value: 1}
    _, err := db.C("gen_id").Find(M{"_id": forCName}).Apply(mgo.Change{Update: M{"$inc": IDInt64}, Upsert: true, ReturnNew: true}, &IDInt64)
    return IDInt64.Value, err
}