mgo golang doesnt update empty array using $set

Question

struct and method:

type Group struct {
    Id                          int64            `bson:"_id,omitempty"`
    MediaFilterExceptionUserIds []int            `bson:"media_filter_exception_user_ids,omitempty"`
}

func (g *Group) Save() error {
    return DB.C("groups").UpdateId(g.Id, bson.M{"$set": &g})
}

func (g *Group) FindById() error {
    return DB.C("groups").FindId(g.Id).One(&g)
}

trying to set media_filter_exception_user_ids to an empty []int{} and it doesn't work:

group := Group{}
group.FindById(123)
group.MediaFilterExceptionUserIds = []int{}
group.Save()

It works when there's an item inside the slice, but empty slice is not set.

Answer 1

MediaFilterExceptionUserIds type should change from []int to *[]int,

type Group struct {
    Id                          int64             `bson:"_id,omitempty"`
    MediaFilterExceptionUserIds *[]int            `bson:"media_filter_exception_user_ids,omitempty"`
}

and then

group.MediaFilterExceptionUserIds = &[]int{}

will set it to an empty array in mongodb