Inserting data into MongoDB with mgo

Question

I'm trying to insert some data in MongoDB using Go.

Here is the data struct:

type Entry struct {
    Id          string `json:"id",bson:"_id,omitempty"`
    ResourceId  int    `json:"resource_id,bson:"resource_id"`
    Word        string `json:"word",bson:"word"`
    Meaning     string `json:"meaning",bson:"meaning"`
    Example     string `json:"example",bson:"example"`
}

This is my insert function:

func insertEntry(db *mgo.Session, entry *Entry) error {
    c := db.DB(*mongoDB).C("entries")
    count, err := c.Find(bson.M{"resourceid": entry.ResourceId}).Limit(1).Count()
    if err != nil {
        return err
    }
    if count > 0 {
        return fmt.Errorf("resource %s already exists", entry.ResourceId)
    }
    return c.Insert(entry)
}

And finally, this is how I call it:

entry := &Entry{
    ResourceId:  resourceId,
    Word:        word,
    Meaning:     meaning,
    Example:     example,
}
err = insertEntry(db, entry)
if err != nil {
    log.Println("Could not save the entry to MongoDB:", err)
}

The trouble is, I was expecting my bson tags to magically work, but they don't. Instead of data being saved as:

{ "_id" : ObjectId("53700d9cd83e146623e6bfb4"), "resource_id" : 7660708, "word" : "Foo" ...}

It gets saved as:

{ "_id" : ObjectId("53700d9cd83e146623e6bfb4"), "id" : "", "resourceid" : 7660708, "word" : "Foo"...}

How can I fix this?

Solution

Change entry to:

type Entry struct {
    Id          string `json:"id" bson:"_id,omitempty"`
    ResourceId  int    `json:"resource_id" bson:"resource_id"`
    Word        string `json:"word" bson:"word"`
    Meaning     string `json:"meaning" bson:"meaning"`
    Example     string `json:"example" bson:"example"`
}

The syntax for Struct Tags does not use commas between tags. I believe this should fix it.

Comments

[Admin]

this is wrong. not only does Id need to be of type bson.ObjectId but the bson tags aren't necessary except for ResourceId which does not get autoconverted to "resource_id". Uppercase struct fields get lowercased by mgo. Only the json lowercase field name is needed.

[Gustavo Niemeyer]

@dalu The _id can actually be of any type. Edit: Well, unless the OP did expect an ObjectId, which isn't entirely clear from the question.

[TrevorSStone]

@dalu as Gustavo said, the _id does not need to be an ObjectId, That is the default, but not always the required choice. Also, nothing is wrong. I personally think that including the bson struct tag is better practice in the long run even if it is the same. Imagine if a future dev comes along and decides to change the variable "Word" to "Title". Without defining the bson tag, they would be altering the datastore without realizing it. Keeping a bson tag helps maintenance down the line IMO and at worse, makes you type a few more characters for clarity.