In order to handle empty data, you can use $ne operator. Let us create a collection with documents. Following is the query>db.handlingAndEmptyDataDemo.insertOne({"StudentName":"John", "StudentCountryName":""}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c9cbd5ca629b87623db1b12") } >db.handlingAndEmptyDataDemo.insertOne({"StudentName":"John", "StudentCountryName":null}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c9cbd6ba629b87623db1b13") } > db.handlingAndEmptyDataDemo.insertOne({"StudentName":"John"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c9cbd71a629b87623db1b14") }Following is the query to display all documents from a collection with the help of find() method> db.handlingAndEmptyDataDemo.find().pretty();This will produce the following output{    "_id" : ObjectId("5c9cbd5ca629b87623db1b12"),    "StudentName" : "John",    "StudentCountryName" : "" } {    "_id" : ObjectId("5c9cbd6ba629b87623db1b13"),    "StudentName" : ... Read More

Use use renameCollection() to change collection name in MongoDB. Following is the syntaxdb.yourOldCollectionName.renameCollection("yourNewCollectionName");Let us create a collection with documents. Following is the query> db.savingInformationDemo.insertOne({"StudentName":"Larry"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c9cb44da629b87623db1b07") } > db.savingInformationDemo.insertOne({"StudentName":"John"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c9cb45da629b87623db1b08") } > db.savingInformationDemo.insertOne({"StudentName":"Mike"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c9cb461a629b87623db1b09") } > db.savingInformationDemo.insertOne({"StudentName":"Sam"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c9cb465a629b87623db1b0a") }Following is the query to display all documents from a collection with the help of find() method> db.savingInformationDemo.find().pretty();This will produce the following output{ "_id" : ObjectId("5c9cb44da629b87623db1b07"), "StudentName" : "Larry" } { ... Read More

Following is the syntax to loop through collections with cursorvar anyVariableName1; var anyVariableName2= db.yourCollectionName.find(); while(yourVariableName2.hasNext()) {    yourVariableName1= yourVariableName2.next(); printjson(yourVariableName1); };Let us create a collection with documents. Following is the query> db.loopThroughCollectionDemo.insertOne({"StudentName":"John", "StudentAge":23}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c9ca81f2d6669774125247f") } > db.loopThroughCollectionDemo.insertOne({"StudentName":"Larry", "StudentAge":21}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c9ca8272d66697741252480") } > db.loopThroughCollectionDemo.insertOne({"StudentName":"Chris", "StudentAge":25}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c9ca8462d66697741252481") } > db.loopThroughCollectionDemo.insertOne({"StudentName":"Robert", "StudentAge":24}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c9ca8632d66697741252482") }Following is the query to display all documents from a collection with the help of find() method> db.loopThroughCollectionDemo.find().pretty();This will ... Read More

To remove all documents from a collection except a single document in MongoDB, use remove() based on some condition. Let us create a collection with documents. Following is the query>db.removeAllDocumentsExceptOneDemo.insertOne({"StudentName":"Larry", "StudentAge":21}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c9c9de42d66697741252478") } >db.removeAllDocumentsExceptOneDemo.insertOne({"StudentName":"Mike", "StudentAge":21, "StudentCountryName":"US"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c9c9dea2d66697741252479") } >db.removeAllDocumentsExceptOneDemo.insertOne({"StudentName":"Chris", "StudentAge":24, "StudentCountryName":"AUS"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c9c9def2d6669774125247a") }Following is the query to display all documents from a collection with the help of find() method> db.removeAllDocumentsExceptOneDemo.find().pretty();This will produce the following output{    "_id" : ObjectId("5c9c9de42d66697741252478"),    "StudentName" : "Larry",    "StudentAge" : ... Read More

You can use $where operator to compare field values in MongoDB. Let us first create a collection with documents> db.comparingFieldDemo.insertOne({"Value1":30, "Value2":40}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c9c99ed2d6669774125246e") } > db.comparingFieldDemo.insertOne({"Value1":60, "Value2":70}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c9c99f62d6669774125246f") } > db.comparingFieldDemo.insertOne({"Value1":160, "Value2":190}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c9c99ff2d66697741252470") } > db.comparingFieldDemo.insertOne({"Value1":200, "Value2":160}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c9c9a0b2d66697741252471") }Following is the query to display all documents from a collection with the help of find() method> db.comparingFieldDemo.find().pretty();This will produce the following output{    "_id" : ObjectId("5c9c99ed2d6669774125246e"),    "Value1" : 30, ... Read More

To find exact array match with values in different order, you can use $all operator. Let us create a collection with documents. Following is the query>db.exactMatchArrayDemo.insertOne({"StudentName":"David", "StudentAge":22, "StudentGameScores":[45, 78, 98]}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c9c94702d6669774125246c") } >db.exactMatchArrayDemo.insertOne({"StudentName":"Chris", "StudentAge":23, "StudentGameScores":[45, 78]}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c9c94a42d6669774125246d") }Following is the query to display all documents from a collection with the help of find() method> db.exactMatchArrayDemo.find().pretty();This will produce the following output{    "_id" : ObjectId("5c9c94702d6669774125246c"),    "StudentName" : "David",    "StudentAge" : 22,    "StudentGameScores" : [       45,       78, ... Read More

Yes, you can do that. First, you need to create an index and then use explain(). Let us first create a MongoDB index. Following is the query:> db.indexOrQueryDemo.ensureIndex({"First":1});This will produce the following output{    "createdCollectionAutomatically" : false,    "numIndexesBefore" : 2,    "numIndexesAfter" : 3,    "ok" : 1 }The query to create second index is as follows> db.indexOrQueryDemo.ensureIndex({"Second":1});This will produce the following output{    "createdCollectionAutomatically" : false,    "numIndexesBefore" : 3,    "numIndexesAfter" : 4,    "ok" : 1 }Following is the query for $or operator with indexes. We have used explain() as well here> db.indexOrQueryDemo.find({$or:[{First:1}, {Second:2}]}).explain();This will produce ... Read More

Following is the syntax to retrieve the documents whose values end with a particular character in MongoDBdb.yourCollectionName.find({yourFieldName: {$regex: "yourEndingCharacter$"}}).pretty();Let us first create a collection with documents>db.retrieveDocumentsWithEndsWithParticularCharacterDemo.insertOne({"StudentName":"Adam", "StudentAge":25, "StudentCountryName":"LAOS"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c9c45b32d66697741252456") } >db.retrieveDocumentsWithEndsWithParticularCharacterDemo.insertOne({"StudentName":"Sam", "StudentAge":24, "StudentCountryName":"ANGOLA"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c9c45c02d66697741252457") } >db.retrieveDocumentsWithEndsWithParticularCharacterDemo.insertOne({"StudentName":"Robert", "StudentAge":21, "StudentCountryName":"AUS"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c9c45cb2d66697741252458") } >db.retrieveDocumentsWithEndsWithParticularCharacterDemo.insertOne({"StudentName":"Chris", "StudentAge":20, "StudentCountryName":"UK"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c9c45d92d66697741252459") } >db.retrieveDocumentsWithEndsWithParticularCharacterDemo.insertOne({"StudentName":"Larry", "StudentAge":23, "StudentCountryName":"US"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c9c45eb2d6669774125245a") }Following is the query to display all documents from a collection ... Read More

Use $unwind operator with $project for to get the first element in an array. Let us create a collection with documents. Following is the query>db.getFirstElementInArrayDemo.insertOne({"StudentName":"John", "StudentSubject":["MongoDB", "Python", "MySQL"]}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c9c41292d6669774125244e") } >db.getFirstElementInArrayDemo.insertOne({"StudentName":"Chris", "StudentSubject":["Java", "C"]}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c9c413f2d6669774125244f") } >db.getFirstElementInArrayDemo.insertOne({"StudentName":"Robert", "StudentSubject":["C++", "Ruby"]}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c9c41532d66697741252450") }Following is the query to display all documents from a collection with the help of find() method> db.getFirstElementInArrayDemo.find().pretty();This will produce the following output{    "_id" : ObjectId("5c9c41292d6669774125244e"),    "StudentName" : "John",    "StudentSubject" : [     ... Read More

To reduce MongoDB storage space after deleting a large amount of data, you need to use repairDatabase(). Let’s say we are using the database “test”. Following is the query to get to the current database> db;This will produce the following outputTestAfter deleting large amount of data, this is how you can reduce the storage space of MongoDB> db.repairDatabase()This will produce the following output{ "ok" : 1 }Here is the screenshot after we implement the above query. This will reduce the storage space: