Auto increment in MongoDB to store sequence of Unique User ID?

To auto increment in MongoDB to store a sequence of unique user id, let us create a collection which contains information about last sequence values of all documents.

Let us first create a collection. The query to create a collection which is as follows −

> db.createSequenceDemo.insertOne({_id:"SID",S_Value:0});
{ "acknowledged" : true, "insertedId" : "SID" }

Now, we will create a function that will generate an auto increment in MongoDB to store sequence. The query is as follows −

> function nextSequence(s) {
   ... var sd = db.createSequenceDemo.findAndModify({
      ... query:{_id: s },
      ... update: {$inc:{S_Value:1}},
      ... new:true
   ... });
   ... return sd.S_Value;
... }

Let us create a collection with some documents and call the above function in order to generate a sequence of unique user id.

The query to create a collection with a document is as follows −

> db.checkSequenceDemo.insertOne({"StudentId":nextSequence("SID"),"StudentName":"Larry","StudentMathMarks":78});
{
   "acknowledged" : true,
   "insertedId" : ObjectId("5c7f61008d10a061296a3c40")
}
> db.checkSequenceDemo.insertOne({"StudentId":nextSequence("SID"),"StudentName":"Mike","StudentMathMarks":89});
{
   "acknowledged" : true,
   "insertedId" : ObjectId("5c7f61118d10a061296a3c41")
}
> db.checkSequenceDemo.insertOne({"StudentId":nextSequence("SID"),"StudentName":"Sam","StudentMathMarks":67});
{
   "acknowledged" : true,
   "insertedId" : ObjectId("5c7f611d8d10a061296a3c42")
}

Display all documents from a collection with the help of find() method. The query is as follows −

> db.checkSequenceDemo.find().pretty();

The following is the output −

{
   "_id" : ObjectId("5c7f61008d10a061296a3c40"),
   "StudentId" : 1,
   "StudentName" : "Larry",
   "StudentMathMarks" : 78
}
{
   "_id" : ObjectId("5c7f61118d10a061296a3c41"),
   "StudentId" : 2,
   "StudentName" : "Mike",
   "StudentMathMarks" : 89
}
{
   "_id" : ObjectId("5c7f611d8d10a061296a3c42"),
   "StudentId" : 3,
   "StudentName" : "Sam",
   "StudentMathMarks" : 67
}

Look at the field “StudentId” which is auto incremented by 1