Limit number of values in a field using MongoDB?

To limit number of values in a field, use $slice operator.

Let us first create a collection with documents −

> db.numberOfValuesDemo.insertOne({"Values":[100,200,300,900,1000,98]});
{
   "acknowledged" : true,
   "insertedId" : ObjectId("5cefb736ef71edecf6a1f6ab")
}

Display all documents from a collection with the help of find() method −

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

Output

{
   "_id" : ObjectId("5cefb736ef71edecf6a1f6ab"),
   "Values" : [
      100,
      200,
      300,
      900,
      1000,
      98
   ]
}

Following is the query to limit number of values in a field using MongoDB −

> db.numberOfValuesDemo.find({},{ "Values": { "$slice": 2 } } );

Output

{ "_id" : ObjectId("5cefb736ef71edecf6a1f6ab"), "Values" : [ 100, 200 ] }