What is MongoDB Auto Increment Sequence?

Why Use It?

MongoDB does not have built-in support for auto-increment like SQL databases. Instead, it uses a 12-byte ObjectId as the default primary key. But in many real-life situations (like ordering systems or invoice numbers), we need a simple number sequence like 1, 2, 3…

We can simulate this auto-increment behavior using a counter collection and a JavaScript function.

 Steps to Create Auto Increment Sequence in MongoDB

1. Create a Sample Collection

First, create a collection that will act like a counter (similar to a sequence in traditional databases):

> db.createCollection("sample") { "ok" : 1 }

2. Insert Initial Sequence Document

Now insert an initial document into this sample collection:

> db.sample.insert({   _id: "item_id",   sequence_value: 0 })

This document will keep track of the current counter value.

3. Create JavaScript Function

This function will fetch the current value and increase it by 1 each time it's called:

function getValueForNextSequence(sequenceName){  var sequenceDoc = db.sample.findAndModify({    query: { _id: sequenceName },    update: { $inc: { sequence_value: 1 } },    new: true  });  return sequenceDoc.sequence_value; }

4. Insert Records Using Auto-Increment ID

Now use the function to insert documents in another collection (STORE) with auto-incremented _id values:

> db.STORE.insert({  _id: getValueForNextSequence("item_id"),  item_short_name: "ABC",  specification: "book",  category: "fictional",  seller: "best_buy",  network: "XYZ",  plan: "regular" })

You can insert more entries the same way:

> db.STORE.insert({  _id: getValueForNextSequence("item_id"),  item_short_name: "DEF",  specification: "book",  category: "fictional",  seller: "best_buy",  network: "GHI",  plan: "premium" })

5. View Inserted Records

Check your inserted documents using:

> db.STORE.find().pretty()

Sample Output:

{  "_id": 1,  "item_short_name": "ABC",  "specification": "book",  "category": "fictional",  "seller": "best_buy",  "network": "XYZ",  "plan": "regular" } {  "_id": 2,  "item_short_name": "DEF",  ... } 

Summary

That’s it! You’ve learned how to simulate an auto increment sequence in MongoDB using a simple counter collection and a JavaScript function in 7 easy steps. This method is handy for applications that need numeric IDs.

If you have any questions, feel free to drop a comment or join our MongoDB training sessions at DebugShala!