For array concatenation, use $concatArrays operator. Let us first create a collection with documents −
>db.arrayConcatenationDemo.insertOne({"TeacherName":["Chris","Robert"],"StudentName":["Mike","Sam"]}); { "acknowledged" : true, "insertedId" : ObjectId("5ce921c078f00858fb12e911") }
Following is the query to display all documents from a collection with the help of find() method −
> db.arrayConcatenationDemo.find().pretty();
This will produce the following output −
{ "_id" : ObjectId("5ce921c078f00858fb12e911"), "TeacherName" : [ "Chris", "Robert" ], "StudentName" : [ "Mike", "Sam" ] }
Following is the query for array concatenation −
> db.arrayConcatenationDemo.aggregate([ { "$project": { "StudentAndTeacherName": { "$concatArrays": [ "$TeacherName", "$StudentName" ] } }} ]);
This will produce the following output −
{ "_id" : ObjectId("5ce921c078f00858fb12e911"), "StudentAndTeacherName" : [ "Chris", "Robert", "Mike", "Sam" ] }