Match between fields in MongoDB aggregation framework?

      You can use $cmp operator for this. To understand the concept, let us create a collection with the document. The query to create a collection with a document is as follows −

> db.matchBetweenFieldsDemo.insertOne({"FirstValue":40,"SecondValue":70}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c92c9625259fcd19549980d") } > db.matchBetweenFieldsDemo.insertOne({"FirstValue":20,"SecondValue":5}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c92c96b5259fcd19549980e") }

Display all documents from a collection with the help of find() method. The query is as follows −

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

The following is the output −

{    "_id" : ObjectId("5c92c9625259fcd19549980d"),    "FirstValue" : 40,    "SecondValue" : 70 } {    "_id" : ObjectId("5c92c96b5259fcd19549980e"),    "FirstValue" : 20, "SecondValue" : 5 }

Here is the query to $match between fields in aggregation framework −

> db.matchBetweenFieldsDemo.aggregate([    ... {$project: {       ...       ... firstGreaterThanOrNot: {$cmp: ['$FirstValue', '$SecondValue']}    ... }},    ... {$match: {firstGreaterThanOrNot:{$gt: 0}}} ... ]);

The following is the output −

{ "_id" : ObjectId("5c92c96b5259fcd19549980e"), "firstGreaterThanOrNot" : 1 }