将方法转换为通用方式，使用mgo查找

I'm trying to get getObj() function will be more general and could work with any type, not only User like in my code. I was thinking in return a interface instead a defined struct, but I can't fit this idea to my code, please could someone give me a hand with this?
Thanks in advance

type User struct {
    FirstName  string        `bson:"first_name"`
    LastName   string        `bson:"last_name"`
}

type Mbase struct {
    coll *mgo.Collection
    sess *mgo.Session
}

func (b *Mbase) getObj(attr string, val string) (res *User, err error) {
    err = b.coll.Find(bson.M{attr: val}).One(&res)
    if err != nil {
        return
    }
    err = nil
    return
}

You can do something like:

func (b *Mbase) GetObj(attr string, val string, result interface{}) error {
    return b.coll.Find(bson.M{attr: val}).One(result)
}

Doesn't feel like the helper is doing much good, though. Find+One itself is already generic. I'd also consider using bson.D{{attr, val}} instead of bson.M if that's all you need.

Also, please consider asking questions in a single forum at a time.