从mgo（MongoDB库）到Golang结构的嵌套结构转换？

Question

I have a struct like this:

type ArticleDocument struct {
    ArticleID    string `json:"article_id" bson:"article_id"`
    ArticleTitle string `json:"article_title" bson:"article_title"`
    Author       string `json:"author" bson:"author"`
    Board        string `json:"board" bson:"board"`
    Content      string `json:"content" bson:"content"`
    Date         string `json:"date" bson:"date"`
    IP           string `json:"ip" bson:"ip"`
    MessageConut struct {
        All     int `json:"all" bson:"all"`
        Boo     int `json:"boo" bson:"boo"`
        Count   int `json:"count" bson:"count"`
        Neutral int `json:"neutral" bson:"neutral"`
        Push    int `json:"push" bson:"push"`
    } `json:"message_count,inline" bson:"message_count,inline"`
    Messages []interface{} `json:"messages" bson:"messages"`
    URL      string        `json:"url" bson:"url"`
}

In MongoDB, my document looks like:

{
    "_id" : ObjectId("5ab1da8133691b034b2be31d"),
    "article_id" : "M.1521548086.A.DCA",
    "article_title" : "some title",
    "author" : "somebody",
    "board" : "some board",
    "content" : "some content",
    "date" : "Tue Mar 20 20:14:42 2018",
    "ip" : "1.1.1.1",
    "message_conut" : {
        "all" : 15,
        "boo" : 0,
        "count" : 14,
        "neutral" : 1,
        "push" : 14
    },
    "messages" : [],
    "url" : "https://xxx.xxx.xxx"
}

In my Golang code, i am trying to use mgo to query this document and print it out, however, all document fields are converted to golang struct correctly except the nested document "MessageConut", all the values in "All", "Boo", "Count", ...etc are zero:

message_count":{"all":0,"boo":0,"count":0,"neutral":0,"push":0}"

Could you please guide how do I solve this issue?