mongoDB : $size : Query array based on size

$size operator selects documents if the array field is a specified size.

> db.employee.find()
{ "_id" : 1, "firstName" : "Joel", "lastName" : "chelli", "salary" : 25000, "hobbies" : [ "watching movies", "playing games" ] }
{ "_id" : 2, "firstName" : "Ananad", "lastName" : "Bandaru", "salary" : 200000, "hobbies" : [ "car drivinig", "watching movies" ] }
{ "_id" : 3, "firstName" : "Gopi", "lastName" : "Battu", "salary" : 65000, "hobbies" : [ "climbing hills", "dancing", "singing" ] }
{ "_id" : 4, "firstName" : "Ritwik", "lastName" : "Mohenthy", "salary" : 50000, "hobbies" : [ "watching movies", "watching movies", "watching movies" ] }
{ "_id" : 5, "firstName" : "RamaKrishna", "lastName" : "Gurram", "salary" : 150000, "hobbies" : [ "hackning sites", "Reading books", "listening music" ] }
{ "_id" : 6, "firstName" : "BalaKrishna", "lastName" : "Gurram", "salary" : 80000, "hobbies" : [ "roaming around", "eating food" ] }
{ "_id" : ObjectId("54ba2de1f1c8f2149c000740"), "name" : "Krishna", "project" : "A350" }
{ "_id" : ObjectId("54ba2dfcf1c8f2149c000741"), "name" : "Krishna", "project" : 4 }
{ "_id" : ObjectId("54ba47c9f1c8f2149c000742"), "name" : "Keerthi", "hobbies" : [ "watching movies", "playing games", "cooking" ] }

1.Get all documents where total number of hobbies is 2.

> db.employee.find({"hobbies" : {$size : 2}})
{ "_id" : 1, "firstName" : "Joel", "lastName" : "chelli", "salary" : 25000, "hobbies" : [ "watching movies", "playing games" ] }
{ "_id" : 2, "firstName" : "Ananad", "lastName" : "Bandaru", "salary" : 200000, "hobbies" : [ "car drivinig", "watching movies" ] }
{ "_id" : 6, "firstName" : "BalaKrishna", "lastName" : "Gurram", "salary" : 80000, "hobbies" : [ "roaming around", "eating food" ] }

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