Check for Existing Document in MongoDB?

You can use findOne() for this. Following is the syntax −

db.yourCollectionName.findOne({yourFieldName: 'yourValue'});

Let us create a collection with documents −

> db.checkExistingDemo.insertOne({"StudentName":"John"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5cbdf90dac184d684e3fa265") } > db.checkExistingDemo.insertOne({"StudentName":"Carol"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5cbdf912ac184d684e3fa266") } > db.checkExistingDemo.insertOne({"StudentName":"Sam"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5cbdf916ac184d684e3fa267") } > db.checkExistingDemo.insertOne({"StudentName":"Mike"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5cbdf91bac184d684e3fa268") }

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

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

This will produce the following output −

{ "_id" : ObjectId("5cbdf90dac184d684e3fa265"), "StudentName" : "John" } { "_id" : ObjectId("5cbdf912ac184d684e3fa266"), "StudentName" : "Carol" } { "_id" : ObjectId("5cbdf916ac184d684e3fa267"), "StudentName" : "Sam" } { "_id" : ObjectId("5cbdf91bac184d684e3fa268"), "StudentName" : "Mike" }

Following is the query to check existing document −

> db.checkExistingDemo.findOne({StudentName: 'Carol'});

This will produce the following output −

{ "_id" : ObjectId("5cbdf912ac184d684e3fa266"), "StudentName" : "Carol" }