How do you implement an auto-incrementing primary ID in MongoDB?

Question

Just like in MYSQL, I want an incrementing ID.

Answer 1

MongoDB provides 2 way to auto increment _id (or custom key) .

• Use Counters Collection
• Optimistic Loop

Counter Collection

---

Here we need to create collection which stores the maximum number of keys and increment by 1 every time when we call this function.

1. STORE FUNCTION

function getNextSequence(collectionName) {
   var ret = db.counters.findAndModify({
               query: { _id: collectionName },
               update: { $inc: { seq: 1 } },
               new: true,
               upsert: true
             });

   return ret.seq;
}

2. INSERT DOC

db.users.insert({
  _id: getNextSequence("USER"),
  name: "Nishchit."
})

Optimistic Loop

---

In this pattern, an Optimistic Loop calculates the incremented _id value and attempts to insert a document with the calculated _id value. If the insert is successful, the loop ends. Otherwise, the loop will iterate through possible _id values until the insert is successful.

1. STORE FUNCTION

function insertDocument(doc, targetCollection) {

    while (1) {

        var cursor = targetCollection.find( {}, { _id: 1 } ).sort( { _id: -1 } ).limit(1);

        var seq = cursor.hasNext() ? cursor.next()._id + 1 : 1;

        doc._id = seq;

        var results = targetCollection.insert(doc);

        if( results.hasWriteError() ) {
            if( results.writeError.code == 11000 /* dup key */ )
                continue;
            else
                print( "unexpected error inserting data: " + tojson( results ) );
        }

        break;
    }
}

2. INSERT DOC

var myCollection = db.USERS;

insertDocument(
   {
     name: "Nishchit Dhanani"
   },
   myCollection
);

Official doc from MongoDB.