Let us first create a collection with documents −> db.demo194.insertOne( ...   { ...      "_id": 101, ...      "details": { ...         "otherDetails": { ...            "List1": ["MongoDB", "MySQL"], ...            "List2": ["Java"], ...            "List3": ["MongoDB", "C"] ...         } ...      } ...   } ...); { "acknowledged" : true, "insertedId" : 101 } > db.demo194.insertOne( {"_id": 102, "details": { "otherDetails": { "List1": ["Java", "C"],        "List2": ["C++"], "List3": ["Python", "Spring"] } } } ... Read More

To improve the execution time of a query, use index along with unique:true. Let us create a collection with documents −> db.demo193.createIndex({"LastName":1}, {unique:true}); {    "createdCollectionAutomatically" : true,    "numIndexesBefore" : 1,    "numIndexesAfter" : 2,    "ok" : 1 } > db.demo193.insertOne({"FirstName":"John", "LastName":"Doe"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e3ade1803d395bdc21346d1") } > db.demo193.insertOne({"FirstName":"John", "LastName":"Smith"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e3ade1f03d395bdc21346d2") } > db.demo193.insertOne({"FirstName":"David", "LastName":"Miller"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e3ade2803d395bdc21346d3") }Display all documents from a collection with the help of find() method −> db.demo193.find();This will produce the following output −{ "_id" ... Read More

To group several fields, use $group in MongoDB. Let us create a collection with documents −> db.demo192.insertOne({"Name":"Chris", "Age":22}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e3adb9f03d395bdc21346cd") } > db.demo192.insertOne({"Name":"David", "Age":21}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e3adba103d395bdc21346ce") } > db.demo192.insertOne({"Name":"Chris", "Age":22}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e3adba503d395bdc21346cf") } > db.demo192.insertOne({"Name":"Mike", "Age":24}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e3adbbf03d395bdc21346d0") }Display all documents from a collection with the help of find() method −> db.demo192.find();This will produce the following output −{ "_id" : ObjectId("5e3adb9f03d395bdc21346cd"), "Name" : "Chris", "Age" : 22 } { "_id" : ObjectId("5e3adba103d395bdc21346ce"), ... Read More

To get values of cursor in MongoDB, use hasNext(). Let us create a collection with documents −> db.demo191.insertOne({"EmployeeId":1, "EmployeeName":"Chris Brown"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e3ad95303d395bdc21346c5") } > db.demo191.insertOne({"EmployeeId":2, "EmployeeName":"David Miller"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e3ad95f03d395bdc21346c6") } > db.demo191.insertOne({"EmployeeId":1, "EmployeeName":"John Doe"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e3ad96803d395bdc21346c7") } > db.demo191.insertOne({"EmployeeId":1, "EmployeeName":"John Smith"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e3ad97003d395bdc21346c8") }Display all documents from a collection with the help of find() method −> db.demo191.find();This will produce the following output −{ "_id" : ObjectId("5e3ad95303d395bdc21346c5"), "EmployeeId" : 1, "EmployeeName" : "Chris ... Read More

To implement aggregation with multiple keys, use aggregate() along with $group. Let us create a collection with documents −> db.demo190.insertOne( ...   { ... ...      "DueDate" : ISODate("2020-01-01"), ...      "Value" : 10, ...      "Name" : "Chris" ...   } ...); {    "acknowledged" : true,    "insertedId" : ObjectId("5e3ad76403d395bdc21346bf") } > > db.demo190.insertOne( ...   { ... ...      "DueDate" : ISODate("2020-02-05"), ...      "Value" : 30, ...      "Name" : "David" ...   } ...); {    "acknowledged" : true,    "insertedId" : ObjectId("5e3ad76403d395bdc21346c0") } > db.demo190.insertOne( ...   { ... Read More

To sort by the sum of specified object inside inner array, use $match along with $sort. Let us create a collection with documents −> db.demo189.insertOne( ...   { ...      "_id" : 100, ...      "List" : [ ...         { ...            "Value" : 10 ...         }, ..         .{ ...            "Value" : 20 ...         }, ...         { ...            "Value" : 10 ...     ... Read More

To find same value multiple times, use $where in MongoDB. Let us create a collection with documents −> db.demo188.insertOne( ...   { ...      "ListOfData":[ ...         {"Data": 100}, ...         {"Data": 200}, ...         {"Data": 100} ...      ] ...   } ...); {    "acknowledged" : true,    "insertedId" : ObjectId("5e3ad1c203d395bdc21346bd") } > db.demo188.insertOne( ...   { ...      "ListOfData":[ ...         {"Data": 100}, ...         {"Data": 200}, ...         {"Data": 300} ...   } ...); { ... Read More

Let us first create a collection with documents −> db.demo187.insertOne( ...    { ...      "_id" : "101", ...      "Details" : [ ...         { "Subject" : "MongoDB" }, ...         { "Subject" : "MySQL" } ...      ] ...   } ...); { "acknowledged" : true, "insertedId" : "101" } > db.demo187.insertOne( ...   { ...      "_id" : "102", ...      "Details" : [ ...         { } ...      ] ...   } ...); { "acknowledged" : true, "insertedId" : "102" ... Read More

Let us first create a collection with documents −> db.demo186.insertOne({"UserEmailId":"JOHN@GMAIL.COM", "UserName":"John"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e399d769e4f06af55199808") } > db.demo186.insertOne({"UserEmailId":"chris@gmail.com", "UserName":"chris"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e399d879e4f06af55199809") } > db.demo186.insertOne({"UserEmailId":"DAVID@GMAIL.COM", "UserName":"David"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e399d979e4f06af5519980a") }Display all documents from a collection with the help of find() method −> db.demo186.find();This will produce the following output −{ "_id" : ObjectId("5e399d769e4f06af55199808"), "UserEmailId" : "JOHN@GMAIL.COM", "UserName" : "John" } { "_id" : ObjectId("5e399d879e4f06af55199809"), "UserEmailId" : "chris@gmail.com", "UserName" : "chris" } { "_id" : ObjectId("5e399d979e4f06af5519980a"), "UserEmailId" : "DAVID@GMAIL.COM", "UserName" : "David" }Following is the ... Read More

To fetch records with $or on the basis of existence, use $or along with $exists. Let us create a collection with documents −>db.demo185.insertOne({_id:101, details:{Name:"Chris", Score:78, Subjects:{"Name":"MySQL"}}}); { "acknowledged" : true, "insertedId" : 101 } > db.demo185.insertOne({_id:102, details:{Name:"Bob", Score:78}}); { "acknowledged" : true, "insertedId" : 102 } >db.demo185.insertOne({_id:103, details:{Name:"David", Score:78, Subjects:{"Name":"MongoDB"}}}); { "acknowledged" : true, "insertedId" : 103 }Display all documents from a collection with the help of find() method −> db.demo185.find();This will produce the following output −{ "_id" : 101, "details" : { "Name" : "Chris", "Score" : 78, "Subjects" : { "Name" : "MySQL" } } } { "_id" ... Read More