To update all elements in an array with a prefix string, use forEach(). Let us first create a collection with documents −
> db.replaceAllElementsWithPrefixDemo.insertOne( { "StudentNames" : [ "John", "Carol" ] } ); { "acknowledged" : true, "insertedId" : ObjectId("5cd91908b50a6c6dd317ad8e") } > > > db.replaceAllElementsWithPrefixDemo.insertOne( { "StudentNames" : [ "Sam" ] } ); { "acknowledged" : true, "insertedId" : ObjectId("5cd9191cb50a6c6dd317ad8f") }
Following is the query to display all documents from a collection with the help of find() method −
> db.replaceAllElementsWithPrefixDemo.find().pretty();
This will produce the following output −
{ "_id" : ObjectId("5cd91908b50a6c6dd317ad8e"), "StudentNames" : [ "John", "Carol" ] } { "_id" : ObjectId("5cd9191cb50a6c6dd317ad8f"), "StudentNames" : [ "Sam" ] }
Following is the query to replace all elements in an array with a prefix string. The prefix string is “MR” −
> db.replaceAllElementsWithPrefixDemo.find().forEach(function (myDocumentValue) { var prefixValue = myDocumentValue.StudentNames.map(function (myValue) { return "MR." + myValue; }); db.replaceAllElementsWithPrefixDemo.update( {_id: myDocumentValue._id}, {$set: {StudentNames: prefixValue}} ); });
Let us check the document once again −
> db.replaceAllElementsWithPrefixDemo.find().pretty();
This will produce the following output −
{ "_id" : ObjectId("5cd91908b50a6c6dd317ad8e"), "StudentNames" : [ "MR.John", "MR.Carol" ] } { "_id" : ObjectId("5cd9191cb50a6c6dd317ad8f"), "StudentNames" : [ "MR.Sam" ] }