选择一个元素数量有限的数组的文档

I have the following structure of the Room type:

type Room struct {
   Id          bson.ObjectId       `json:"id" bson:"_id,omitempty"`
   Title       string              `json:"title" bson:"title"`
   Description string              `json:"description" bson:"description,omitempty"`
   Type        string              `json:"type" bson:"type,omitempty"`
   AdminId     bson.ObjectId       `json:"admin_id" bson:"admin_id"`
   CreatedOn   time.Time           `json:"created_on" bson:"created_on"`
   Messages    []Message           `json:"messages" bson:"messages,omitempty"`}

The type struct Message is embedded, which has the following structure

type Message struct {
   Id       bson.ObjectId   `json:"id" bson:"_id,omitempty"`
   Text     string          `json:"text" bson:"text"`
   Author       Author          `json:"author" bson:"author"`
   CreatedOn    time.Time   `json:"createdon" bson:"created_on"`
   Reply        []Message   `json:"reply" bson:"reply,omitempty"`}

Using this code I can extract all the fields of the collection.

room := &Room{}
roomsCollection := session.DB(config.Data.DB.Database).C("Rooms")
err := roomsCollection.Find(bson.M{"_id": room_id}).One(room)
if err != nil {
    panic(err)
    return nil, err
}

This gives the rooms with all the messages in the given documents. The question is, can I limit the length of nested Messages array in each document?

So, the solution was really simple. To perform this we can use $slice. The result query will be as following:

roomsCollection.Find(bson.M{"_id": room_id})).Select(bson.M{ "messages": bson.M{ "$slice": 5} } ).One(room)

Special thanks to @Veeram for correct answer.