Here, $push can be used to add new documents in nested array. To understand the above $push concept, let us create a collection with nested array document. The query to create a collection with document is as follows:>db.nestedArrayDemo.insertOne({"EmployeeName":"Larry", "EmployeeSalary":9000, "EmployeeDetails":    [{"EmployeeDOB":new Date('1990-01-21'), "EmployeeDepartment":"ComputerScience", "EmployeeProject":    [{"Technology":"C", "Duration":6}, {"Technology":"Java", "Duration":7}]}]});The following is the output:{    "acknowledged" : true,    "insertedId" : ObjectId("5c6d73090c3d5054b766a76e") }Now you can display documents from a collection with the help of find() method. The query is as follows:> db.nestedArrayDemo.find().pretty();The following is the output:{    "_id" : ObjectId("5c6d73090c3d5054b766a76e"),    "EmployeeName" : "Larry",    "EmployeeSalary" : 9000,    "EmployeeDetails" ... Read More

You can use length to query for documents where array size is greater than 1:db.yourCollectionName.find({$where:"this.yourArrayDocumentName.length > 1"}).pretty();To understand the above syntax, let us create a collection with some documents. The query is as follows to create a collection with documents:>db.arrayLengthGreaterThanOne.insertOne({"StudentName":"Larry", "StudentTechnicalSubje ct":["Java", "C", "C++"]}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c6d6c4c0c3d5054b766a76a") } >db.arrayLengthGreaterThanOne.insertOne({"StudentName":"Maxwell", "StudentTechnicalSu bject":["MongoDB"]}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c6d6c660c3d5054b766a76b") } >db.arrayLengthGreaterThanOne.insertOne({"StudentName":"Maxwell", "StudentTechnicalSu bject":["MySQL", "SQL Server", "PL/SQL"]}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c6d6c800c3d5054b766a76c") }Display all documents from a collection with the help of find() method. The query is as follows:> db.arrayLengthGreaterThanOne.find().pretty();The ... Read More

To update the objects in a document’s array, you need to use update() method. To understand the update() method, let us create a collection with document. The query to create a collection with document is as follows:> db.updateObjects.insertOne({"CustomerId":1, "CustomerName":"Larry", "TotalItems":100, ... "ItemDetails":[ ... { ... "NameOfItem":"Item_1", ... "Amount":450 ... }, ... { ... "NameOfItem":"Item_2", ... "Amount":500 ... }, ... { ... "NameOfItem":"Item_3", ... "Amount":200 ... } ... ] ... } ... );The following is the output:{    "acknowledged" : true,    "insertedId" : ObjectId("5c6d688b0c3d5054b766a769") }Now you can display documents from a collection with the help of find() method. The query ... Read More

You can use aggregate and unwind the array list before applying match. To understand the above concept, let us create a collection with documents. The query to create a collection with document is as follows:> db.filterArray.insertOne( { "L": [{ "N":1 }, { "N":2 } , { "N":3 }, { "N":4 }, { "N":5 } ]});The following is visible after running the above query:{    "acknowledged" : true,    "insertedId" : ObjectId("5c6d63f2734e98fc0a434aeb") }Display document from a collection with the help of find() method. The query is as follows:> db.filterArray.find().pretty();The following is the output:{    "_id" : ObjectId("5c6d63f2734e98fc0a434aeb"),    "L" : [ ... Read More

To get a random record from MongoDB, you can use aggregate function. The syntax is as follows:db.yourCollectionName.aggregate([{$sample:{size:1}}]);To understand the above syntax, let us create a collection with some documents. The query to create collection is as follows:>db.employeeInformation.insert({"EmployeeId":1, "EmployeeName":"Maxwell", "EmployeeAge":26}); WriteResult({ "nInserted" : 1 }) >db.employeeInformation.insert({"EmployeeId":2, "EmployeeName":"David", "EmployeeAge":25}); WriteResult({ "nInserted" : 1 }) >db.employeeInformation.insert({"EmployeeId":3, "EmployeeName":"Carol", "EmployeeAge":24}); WriteResult({ "nInserted" : 1 }) >db.employeeInformation.insert({"EmployeeId":4, "EmployeeName":"Bob", "EmployeeAge":28}); WriteResult({ "nInserted" : 1 }) >db.employeeInformation.insert({"EmployeeId":5, "EmployeeName":"Sam", "EmployeeAge":27); WriteResult({ "nInserted" : 1 })Now you can display all documents from a collection with the help of find() method. The query is as follows:> db.employeeInformation.find().pretty();The following is the output:{ ... Read More

You can use $where operator along with find() method to compare two fields in MongoDB. The syntax is as follows:db.yourCollectionName.find({$where:”yourCondition”}).pretty();To understand the above syntax, let us create a collection with some documents. The query to create a collection with documents is as follows:>db.compareTwoFields.insert({"Id":1, "FullName":{"FirstName":"John", "LastName":"Smith"}, "BranchName":"ComputerScience"}); WriteResult({ "nInserted" : 1 }) >db.compareTwoFields.insert({"Id":2, "FullName":{"FirstName":"Smith", "LastName":"Smith"}, "BranchName":"Civil"}); WriteResult({ "nInserted" : 1 }) >db.compareTwoFields.insert({"Id":3, "FullName":{"FirstName":"David", "LastName":"Smith"}, "BranchName":"Mechanical"}); WriteResult({ "nInserted" : 1 })Now you can display all documents from a collection with the help of find() method. The query is as follows:> db.compareTwoFields.find().pretty();The following is the output:{    "_id" : ObjectId("5c6c237568174aae23f5ef64"),   ... Read More

The syntax to get names of all keys in the collection is as follows:var yourVariableName1=db.yourCollectionName.findOne(); for(var yourVariableName 2 in yourVariableName1) { print(yourVariableName); }To understand the above syntax, let us create a collection with documents. The collection name we are creating is “studentGetKeysDemo”.The following is the query to create documents:>db.studentGetKeysDemo.insert({"StudentId":1, "StudentName":"Larry", "StudentAge":23, "StudentAddress":"US", ... "StudentHobby":["Cricket", "Football", "ReadingNovel"],    "StudentMathMarks":89, "StudentDOB":ISODate('1998-04-06')});The following is the output:WriteResult({ "nInserted" : 1 })Display all documents from a collection with the help of find() method. The query is as follows:> db.studentGetKeysDemo.find().pretty();The following is the output:{    "_id" : ObjectId("5c6c12dd68174aae23f5ef5f"),    "StudentId" : 1,    "StudentName" : ... Read More

You can easily query MongoDB with “like”:db.yourCollectionName.find({"yourFieldName" : /.*yourMatchingValue.*/}).pretty();To understand the above syntax, let us create a collection with some documents. Here, we have a collection with the name ‘employee’. The query is as follows:> db.employee.insert({"EmployeeName":"John", "EmployeeSalary":450000}); WriteResult({ "nInserted" : 1 }) > db.employee.insert({"EmployeeName":"Carol", "EmployeeSalary":150000}); WriteResult({ "nInserted" : 1 }) > db.employee.insert({"EmployeeName":"James", "EmployeeSalary":550000}); WriteResult({ "nInserted" : 1 }) > db.employee.insert({"EmployeeName":"Jace", "EmployeeSalary":670000}); WriteResult({ "nInserted" : 1 }) > db.employee.insert({"EmployeeName":"Larry", "EmployeeSalary":1000000}); WriteResult({ "nInserted" : 1 })Now you can display all documents from a collection using find() method. The query is as follows:> db.employee.find().pretty();The following is the output:{    "_id" : ObjectId("5c6c0b2e68174aae23f5ef59"),   ... Read More

Use operator $gte and $lt to find objects between two dates in MongoDB. To understand these operators, let us create a collection.Creating a collection here:>db.order.insert({"OrderId":1, "OrderAddrees":"US", "OrderDateTime":ISODate("2019-02-19")}; WriteResult({ "nInserted" : 1 }) >db.order.insert({"OrderId":2, "OrderAddrees":"UK", "OrderDateTime":ISODate("2019-02-26")}; WriteResult({ "nInserted" : 1 })Display all documents from the collection with the help of find() method. The query is as follows:> db.order.find().pretty();The following is the output:{    "_id" : ObjectId("5c6c072068174aae23f5ef57"),    "OrderId" : 1,    "OrderAddrees" : "US",    "OrderDateTime" : ISODate("2019-02-19T00:00:00Z") } {    "_id" : ObjectId("5c6c073568174aae23f5ef58"),    "OrderId" : 2,    "OrderAddrees" : "UK",    "OrderDateTime" : ISODate("2019-02-26T00:00:00Z") }Here is the query ... Read More

You can use aggregate function to update MongoDB field using the value of another field. Here, we will create two collections:namestudentInformation CollectionThe query to create first collection with documents is as follows:> db.name.insert({"FirstName":"John", "LastName":"Smith"}); WriteResult({ "nInserted" : 1 })Now you can display all documents from the collection with the help of find() method. The query is as follows:> db.name.find().pretty();The following is the output that displays the collection “name” documents:{    "_id" : ObjectId("5c6c00dd68174aae23f5ef55"),    "FirstName" : "John",    "LastName" : "Smith" } CollectionThe query to create second collection with documents is as follows:> db.studentInformation.insert({"StudentFirstName":"Carol", "StudentLastName":"Taylor"}); WriteResult({ "nInserted" : 1 })Now ... Read More