How to find only a single document satisfying the criteria in MongoDB?

To find only a single document, use findOne() in MongoDB. Let us create a collection with documents −

> db.demo116.insertOne({"EmployeeId":101,"EmployeeName":"John"});
{
   "acknowledged" : true,
   "insertedId" : ObjectId("5e2eff98d8f64a552dae635b")
}
> db.demo116.insertOne({"EmployeeId":102,"EmployeeName":"Bob"});
{
   "acknowledged" : true,
   "insertedId" : ObjectId("5e2eff9fd8f64a552dae635c")
}
> db.demo116.insertOne({"EmployeeId":103,"EmployeeName":"David"});
{
   "acknowledged" : true,
   "insertedId" : ObjectId("5e2effa5d8f64a552dae635d")
}
> db.demo116.insertOne({"EmployeeId":102,"EmployeeName":"Mike"});
{
   "acknowledged" : true,
   "insertedId" : ObjectId("5e2effb7d8f64a552dae635e")
}

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

> db.demo116.find();

This will produce the following output −

{ "_id" : ObjectId("5e2eff98d8f64a552dae635b"), "EmployeeId" : 101, "EmployeeName" : "John" }
{ "_id" : ObjectId("5e2eff9fd8f64a552dae635c"), "EmployeeId" : 102, "EmployeeName" : "Bob" }
{ "_id" : ObjectId("5e2effa5d8f64a552dae635d"), "EmployeeId" : 103, "EmployeeName" : "David" }
{ "_id" : ObjectId("5e2effb7d8f64a552dae635e"), "EmployeeId" : 102, "EmployeeName" : "Mike" }

Following is the query to find only a single document in MongoDB −

> db.demo116.findOne({"EmployeeId":102});

This will produce the following output −

{
   "_id" : ObjectId("5e2eff9fd8f64a552dae635c"),
   "EmployeeId" : 102,
   "EmployeeName" : "Bob"
}