How to find two random documents in a MongoDB collection of 6?

Let us first create a collection and add some documents to it

> db.twoRandomDocumentDemo.insertOne({"StudentId":10}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c9ec9aad628fa4220163b87") } > db.twoRandomDocumentDemo.insertOne({"StudentId":100}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c9ec9add628fa4220163b88") } > db.twoRandomDocumentDemo.insertOne({"StudentId":45}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c9ec9b0d628fa4220163b89") } > db.twoRandomDocumentDemo.insertOne({"StudentId":55}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c9ec9b3d628fa4220163b8a") } > db.twoRandomDocumentDemo.insertOne({"StudentId":5}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c9ec9b7d628fa4220163b8b") } > db.twoRandomDocumentDemo.insertOne({"StudentId":7}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c9ec9bad628fa4220163b8c") }

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

> db.twoRandomDocumentDemo.find();

This will produce the following output

{ "_id" : ObjectId("5c9ec9aad628fa4220163b87"), "StudentId" : 10 } { "_id" : ObjectId("5c9ec9add628fa4220163b88"), "StudentId" : 100 } { "_id" : ObjectId("5c9ec9b0d628fa4220163b89"), "StudentId" : 45 } { "_id" : ObjectId("5c9ec9b3d628fa4220163b8a"), "StudentId" : 55 } { "_id" : ObjectId("5c9ec9b7d628fa4220163b8b"), "StudentId" : 5 } { "_id" : ObjectId("5c9ec9bad628fa4220163b8c"), "StudentId" : 7 }

Following is the query to get 2 random documents out of 6. Set the size as 2 since we want only 2 documents.

> db.twoRandomDocumentDemo.aggregate([{$sample: {size: 2}}]);

This will produce the following output

{ "_id" : ObjectId("5c9ec9b3d628fa4220163b8a"), "StudentId" : 55 } { "_id" : ObjectId("5c9ec9aad628fa4220163b87"), "StudentId" : 10 }

Here is the second case when you run the above query once again to get different documents

> db.twoRandomDocumentDemo.aggregate([{$sample: {size: 2}}]);

This will produce the following output

{ "_id" : ObjectId("5c9ec9add628fa4220163b88"), "StudentId" : 100 } { "_id" : ObjectId("5c9ec9b7d628fa4220163b8b"), "StudentId" : 5 }