Map nested struct to MongoDB: .Decode(&dto)

Programming
,
1

I am having an issue retrieving a JSON document that was created with no issue. The nested object within the JSON is empty, despite .Decode being used correctly.

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"`
}

I am having an issue retrieving a JSON document with an empty nested object. .Decode should map the nested values, however, the resulting JSON is still empty.

2

The issue might be caused by the incorrect field name mapping in the Course struct.

In the struct definition, the nested object is named Details instead of course_details. To fix the issue, update the field name in the struct definition to match the JSON key:

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:"details"`
}

After making this change, the .Decode method should correctly map the nested values of the JSON document.