CODEWITHSUNDEEP
mongodbgo
Depado
Depado

Reputation: 4929

Create a custom ID with Mgo

I'm currently starting with GoLang and MongoDB.I'm writing a small web application, a blog to be more specific (which is like the first webapp I write when I try new languages). Everything works fine with MGO even if I had some troubles at first. But now I'd like to access each blog entry (articles will be referred as entries to stick with my models) separately. I could use the ObjectID in the url. But that's damn ugly. For example :
mydomain.com/entries/543fd8940e82533995000002/
That's not user friendly. I did a lot of research on the internet to find a suitable solution, because using any other database engine I could just use the id (and that would be fine).

Could someone help me with the creation of a custom (public) id which would auto-increment when I insert a new entry and that I could use in the url ?

Here is the code of my model for now :

package models

import (
    "time"

    "labix.org/v2/mgo"
    "labix.org/v2/mgo/bson"
)

type (
    Entries []Entry
    Entry   struct {
        ID      bson.ObjectId `bson:"_id,omitempty"`
        Title   string        `bson:"title"`
        Short   string        `bson:"short"`
        Content string        `bson:"content"`
        Posted  time.Time     `bson:"posted"`
    }
)

// Insert an entry to the database
func InsertEntry(database *mgo.Database, entry *Entry) error {
    entry.ID = bson.NewObjectId()
    return database.C("entries").Insert(entry)
}

// Find an entry by id
func GetEntryByID(database *mgo.Database, id string) (entry Entry, err error) {
    bid := bson.ObjectIdHex(id)
    err = database.C("entries").FindId(bid).One(&entry)
    return
}

// Retrieves all the entries
func AllEntries(database *mgo.Database) (entries Entries, err error) {
    err = database.C("entries").Find(nil).All(&entries)
    return
}

// Retrieve all the entries sorted by date.
func AllEntriesByDate(database *mgo.Database) (entries Entries, err error) {
    err = database.C("entries").Find(nil).Sort("-posted").All(&entries)
    return
}

// Counts all the entries.
func CountAllEntries(database *mgo.Database) (count int, err error) {
    count, err = database.C("entries").Find(nil).Count()
    return
}

Upvotes: 4

Views: 8152

Answers (1)

Tug Grall
Tug Grall

Reputation: 3510

As you know the _id is a mandatory field, that is automatically fill by the driver when you do not set it. This is the behavior that you have in your current application/code. You can find information about this type and its generation here: http://docs.mongodb.org/manual/reference/object-id/

However, you can create your own _id and set the value to anything that makes sense for your business.

This is why I am do not understand the following statement:

I did a lot of research on the internet to find a suitable solution, because using any other database engine I could just use the id (and that would be fine).

You can use any value you want as soon as it is unique for your collection.

About the auto-increment, MongoDB does not provide any auto increment field, so you have to implement it yourself, and call the increment from your application.

For example you create a new collection that contains your "sequences/counters": (showing shell commands not go)

{
  _id : "entry",
  sequence : 0
}

Then when you want an new id for your document you have first to update, with a findand modify the document you have created with a simple $inc operation

var ret = db.counters.findAndModify(
          {
            query: { _id: "entry" },
            update: { $inc: { seq: 1 } },
            new: true
          }
   );

You can then use the returned value into you new document as an _id.

This pattern is documented here: http://docs.mongodb.org/manual/tutorial/create-an-auto-incrementing-field/

Upvotes: 4

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