How to use $slice operator to get last element of array in MongoDB?

To get the last element of array in MongoDB, use the following syntax

db.yourCollectionName.find({},{yourArrayFieldName:{$slice:-1}});

Let us first create a collection with documents

>db.getLastElementOfArrayDemo.insertOne({"StudentName":"James","StudentMathScore":[78,68,98]});
{
   "acknowledged" : true,
   "insertedId" : ObjectId("5c9d2d71a629b87623db1b2e")
}
>db.getLastElementOfArrayDemo.insertOne({"StudentName":"Chris","StudentMathScore":[88,56,34]});
{
   "acknowledged" : true,
   "insertedId" : ObjectId("5c9d2d83a629b87623db1b2f")
}
>db.getLastElementOfArrayDemo.insertOne({"StudentName":"Larry","StudentMathScore":[99]});
{
   "acknowledged" : true,
   "insertedId" : ObjectId("5c9d2d8ea629b87623db1b30")
}
>db.getLastElementOfArrayDemo.insertOne({"StudentName":"Robert","StudentMathScore":[90,78,67,66,75,73]});
{
   "acknowledged" : true,
   "insertedId" : ObjectId("5c9d2dada629b87623db1b31")
}

Following is the query to display all documents from a collection with the help of find() method

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

This will produce the following output

{
   "_id" : ObjectId("5c9d2d71a629b87623db1b2e"),
   "StudentName" : "James",
   "StudentMathScore" : [
      78,
      68,
      98
   ]
}
{
   "_id" : ObjectId("5c9d2d83a629b87623db1b2f"),
   "StudentName" : "Chris",
   "StudentMathScore" : [
      88,
      56,
      34
   ]
}
{
   "_id" : ObjectId("5c9d2d8ea629b87623db1b30"),
   "StudentName" : "Larry",
   "StudentMathScore" : [
      99
   ]
}
{
   "_id" : ObjectId("5c9d2dada629b87623db1b31"),
   "StudentName" : "Robert",
   "StudentMathScore" : [
      90,
      78,
      67,
      66,
      75,
      73
   ]
}

Following is the query to get the last element of array in MongoDB

> db.getLastElementOfArrayDemo.find({},{StudentMathScore:{$slice:-1}});

This will produce the following output

{ "_id" : ObjectId("5c9d2d71a629b87623db1b2e"), "StudentName" : "James", "StudentMathScore" : [ 98 ] }
{ "_id" : ObjectId("5c9d2d83a629b87623db1b2f"), "StudentName" : "Chris", "StudentMathScore" : [ 34 ] }
{ "_id" : ObjectId("5c9d2d8ea629b87623db1b30"), "StudentName" : "Larry", "StudentMathScore" : [ 99 ] }
{ "_id" : ObjectId("5c9d2dada629b87623db1b31"), "StudentName" : "Robert",
"StudentMathScore" : [ 73 ] }

George John

Published on 12-Apr-2019 11:24:54