Mongodb 使用mongo'db.Decode(&dto)映射一个嵌套的 struct

我有一个模型，可以创建一个没有问题的JSON文档，但检索它会导致嵌套的JSON对象为空.

func (r *CourseRepo) GetCourseById(ctx context.Context, id string) (Course, error) {
    clog := log.GetLoggerFromContext(ctx)

    var course Course

    objID, err := primitive.ObjectIDFromHex(id)
    if err != nil {
        return course, err
    }

    filter := bson.M{"_id": objID}

    err = r.collection.FindOne(ctx, filter).Decode(&course)
    if err != nil {
        clog.ErrorCtx(err, log.Ctx{"msg": "an error occurred while finding a course"})

        return course, err
    }

    return course, nil
}

struct

type Course struct {
    ObjectId    primitive.ObjectID `bson:"_id, omitempty"`
    Id          string             `json:"id"`
    Title       string             `json:"title"`
    Description string             `json:"description"`
    Lessons     string             `json:"lessons"`
    Duration    string             `json:"duration"`
    Details     struct {
        Title             string `json:"title"`
        Instructor        string `json:"instructor"`
        Introduction      string `json:"introduction"`
        Learn             string `json:"learn"`
        Topics            string `json:"topics"`
        Prerequisites     string `json:"prerequisites"`
        Goal              string `json:"goal"`
        AdditionalDetails string `json:"additionalDetails"`
        HighLevelOverview string `json:"highLevelOverview"`
    } `json:"course_details"`
}

结果

{
    "data": {
        "ObjectId": "64953ac1bf06bfdd7936cad8",
        "id": "",
        "title": "Java 算法rithms",
        "description": "An awesome course",
        "lessons": "4",
        "duration": "10 hours",
        "course_details": {
            "title": "",
            "instructor": "",
            "introduction": "",
            "learn": "",
            "topics": "",
            "prerequisites": "",
            "goal": "",
            "additionalDetails": "",
            "highLevelOverview": ""
        }
    },
    "metadata": "none"
}

根据我所读到的内容，Decode也应该映射Nest值吗？