Let us create a collection with documents −> db.demo196.insertOne( ...   { ... ...      "Id" : "101", ...      "details" : [ ...         { ...            "FirstName" : "Chris", ...            "LastName" : "Brown", ...            "Score" : 45 ...         }, ...         { ...            "FirstName" : "David", ...            "LastName" : "Miller", ...            "Score" : 87 ...     ... Read More

To return a list of specific values, use map(). Let us create a collection with documents −> db.demo195.insertOne({"Subject":"MySQL"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e3af3f203d395bdc21346d4") } > db.demo195.insertOne({"Subject":"MongoDB"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e3af3f703d395bdc21346d5") } > db.demo195.insertOne({"Subject":"Java"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e3af3fa03d395bdc21346d6") }Display all documents from a collection with the help of find() method −> db.demo195.find();This will produce the following output −{ "_id" : ObjectId("5e3af3f203d395bdc21346d4"), "Subject" : "MySQL" } { "_id" : ObjectId("5e3af3f703d395bdc21346d5"), "Subject" : "MongoDB" } { "_id" : ObjectId("5e3af3fa03d395bdc21346d6"), "Subject" : "Java" }Following is the query to return a ... Read More

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