For this, use the $addToSet operator. Let us first create a collection with documents −
> db.findDocumentWithCommonFieldsDemo.insertOne( { "UserId":1, "UserName":"Carol" } ); { "acknowledged" : true, "insertedId" : ObjectId("5cdf8ebebf3115999ed51200") } > db.findDocumentWithCommonFieldsDemo.insertOne( { "UserId":2, "UserName":"David" } ); { "acknowledged" : true, "insertedId" : ObjectId("5cdf8ebebf3115999ed51201") } > > db.findDocumentWithCommonFieldsDemo.insertOne( { "UserId":1, "UserName":"Sam" } ); { "acknowledged" : true, "insertedId" : ObjectId("5cdf8ebebf3115999ed51202") }
Following is the query to display all documents from a collection with the help of find() method −
> db.findDocumentWithCommonFieldsDemo.find();
This will produce the following output −
{ "_id" : ObjectId("5cdf8ebebf3115999ed51200"), "UserId" : 1, "UserName" : "Carol" } { "_id" : ObjectId("5cdf8ebebf3115999ed51201"), "UserId" : 2, "UserName" : "David" } { "_id" : ObjectId("5cdf8ebebf3115999ed51202"), "UserId" : 1, "UserName" : "Sam" }
Following is the query to find all documents with common fields in MongoDB −
> db.findDocumentWithCommonFieldsDemo.aggregate({$group : {_id : "$UserId", "UserDetails": {$addToSet : "$UserName"}}});
This will produce the following output −
{ "_id" : 2, "UserDetails" : [ "David" ] } { "_id" : 1, "UserDetails" : [ "Sam", "Carol" ] }