How to add auto increment to existing collection in mongodb/node.js?

Question

Is there any methods or packages, that can help me add auto increments to existing collection? Internet full of information, about how to add AI before you create collection, bu

Answer 1

MongoDB reserves the _id field in the top level of all documents as a primary key. _id must be unique, and always has an index with a unique constraint. It is an auto-incrementing field. However, it is possible to define your own auto-incrementing field following the tutorial in the MongoDB documentation.

Tutorial link: https://docs.mongodb.com/v3.0/tutorial/create-an-auto-incrementing-field/

Answer 2

MongoDB does not have an inbuilt auto-increment functionality.

Create a new collection to keep track of the last sequence value used for insertion:

db.createCollection("counter")

It will hold only one record as:

db.counter.insert({_id:"mySequence",seq_val:0})

Create a JavaScript function as:

function getNextSequenceVal(seq_id){
   // find record with id seq_id and update the seq_val by +1
   var sequenceDoc = db.counter.findAndModify({
      query:{_id: seq_id},
      update: {$inc:{seq_val:1}},
      new:true
   });

   return sequenceDoc.seq_val;
}

To update all the already existing values in your existing collection, this should work (For the empty {}, you can place your conditions if you want to update some documents only):

db.myCollection.update({},
   {$set:{'_id':getNextSequenceVal("mySequence")}},{multi:true})

Now you can insert new records into your existing collection as:

db.myCollection.insert({
   "_id":getNextSequenceVal("mySequence"),
   "name":"ABC"
})