How to concatenate results in MongoDB?

You can concatenate results with the help of forEach(). Let us first create a collection with documents −

> db.concatenateDemo.insertOne({"Name":"John","Age":21}); {    "acknowledged" : true,    "insertedId" : ObjectId("5cc80dd88f9e6ff3eb0ce448") } > db.concatenateDemo.insertOne({"Name":"Carol","Age":23}); {    "acknowledged" : true,    "insertedId" : ObjectId("5cc80de18f9e6ff3eb0ce449") }

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

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

This will produce the following output −

{    "_id" : ObjectId("5cc80dd88f9e6ff3eb0ce448"),    "Name" : "John",    "Age" : 21 } {    "_id" : ObjectId("5cc80de18f9e6ff3eb0ce449"),    "Name" : "Carol",    "Age" : 23 }

Here is the query to concatenate results −

> db.concatenateDemo.find().forEach( function (result) {result.NameAndAge = result.Name + ' ' + result.Age; printjson(result); } );

This will produce the following output −

{    "_id" : ObjectId("5cc80dd88f9e6ff3eb0ce448"),    "Name" : "John",    "Age" : 21,    "NameAndAge" : "John 21" } {    "_id" : ObjectId("5cc80de18f9e6ff3eb0ce449"),    "Name" : "Carol",    "Age" : 23,    "NameAndAge" : "Carol 23" }