To create a collection correctly you need to use a MongoDB object in call i.e.db.createCollection("yourCollectionName");Let us implement the above syntax in order to create a collection and call it using a MongoDB object −> use sample; switched to db sample > db.createCollection("employeeInformation"); { "ok" : 1 }Display all the collections from the above ‘sample’ database −> db.getCollectionNames();This will produce the following output −[    "arraySizeErrorDemo",    "atleastOneMatchDemo",    "basicInformationDemo",    "combinedAndOrDemo",    "convertSQLQueryDemo",    "copyThisCollectionToSampleDatabaseDemo",    "countOrSizeDemo",    "distinctOnMultipleFieldsDemo",    "documentWithAParticularFieldValueDemo",    "employee",    "employeeInformation",    "findListOfIdsDemo",    "findMimimumElementInArrayDemo",    "findSubstring",    "getAllRecordsFromSourceCollectionDemo",    "getElementWithMaxIdDemo",    "insertDocumentWithDateDemo",    "internalArraySizeDemo", ... Read More

Let us first create a collection with documents −> db.embeddedDocumentDemo.insertOne( ...    { ...       "CustomerDetails":[ ...          {"CustomerName":"Chris", "CustomerPurchasePrice":3000}, ...          {"CustomerName":"Robert", "CustomerPurchasePrice":4500}, ...          {"CustomerName":"David", "CustomerPurchasePrice":1000}, ...       ] ...    } ... ); {    "acknowledged" : true,    "insertedId" : ObjectId("5cd32347edc6604c74817ccd") }Following is the query to display all documents from a collection with the help of find() method −> db.embeddedDocumentDemo.find().pretty();This will produce the following output −{    "_id" : ObjectId("5cd32347edc6604c74817ccd"),    "CustomerDetails" : [       {          "CustomerName" ... Read More

Let us first create a collection with documents −> db.projectionAnElementDemo.insertOne( ...    { ...       "CustomerId":100, ...       "CustomerDetails": [ ...          { ...             "CustomerName": "Chris", ...             "CustomerCountryName": "US" ...          }, ...          { ...             "CustomerName": "Robert", ...             "CustomerCountryName": "UK" ...          } ...       ] ...    } ... ); {    "acknowledged" : true,   ... Read More

You can use $set operator for this. Let us first create a collection with documents −> db.updateSubObjectDemo.insertOne( ...    { ... ...       "ClientId" : 100, ...       "ClientDetails" : { ...          "ClientFirstName" : "Adam" ...       } ...    } ... ); {    "acknowledged" : true,    "insertedId" : ObjectId("5cd31434b64f4b851c3a13e9") }Following is the query to display all documents from a collection with the help of find() method −> db.updateSubObjectDemo.find().pretty();This will produce the following output −{    "_id" : ObjectId("5cd31434b64f4b851c3a13e9"),    "ClientId" : 100,    "ClientDetails" : {   ... Read More

Let us first create a collection with a document −>db.replacingEntireDocumentDemo.insertOne({"StudentFirstName":"John", "StudentLastName":"Smith", "StudentCountryName":"US"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5cd3119bb64f4b851c3a13e8") }Following is the query to display document from a collection with the help of find() method −> db.replacingEntireDocumentDemo.find().pretty();This will produce the following output −{    "_id" : ObjectId("5cd3119bb64f4b851c3a13e8"),    "StudentFirstName" : "John",    "StudentLastName" : "Smith",    "StudentCountryName" : "US" }Following is the query to update a MongoDB document while replacing the entire document −>db.replacingEntireDocumentDemo.update({"StudentFirstName":"John", "StudentLastName":"Smith", "StudentCountryName":"US"}, {"StudentFirstName":"David", "StudentLastName":"Miller", "StudentCountryName":"AUS"}); WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })Let us display all the records from the collection ... Read More

Use unique and set it to TRUE. Let us implement the same by creating index and setting two columns to unique −>db.keepTwoColumnsUniqueDemo.createIndex({"StudentFirstName":1, "StudentLastName":1}, {unique:true}); {    "createdCollectionAutomatically" : true,    "numIndexesBefore" : 1,    "numIndexesAfter" : 2,    "ok" : 1 }Now you can insert documents in the above collection −>db.keepTwoColumnsUniqueDemo.insertOne({"StudentFirstName":"John", "StudentLastName":"Smith", "StudentAge":21}); {    "acknowledged" : true,    "insertedId" : ObjectId("5cd30fd7b64f4b851c3a13e5") } >db.keepTwoColumnsUniqueDemo.insertOne({"StudentFirstName":"John", "StudentLastName":"Doe", "StudentAge":23}); {    "acknowledged" : true,    "insertedId" : ObjectId("5cd30fe5b64f4b851c3a13e6") } >db.keepTwoColumnsUniqueDemo.insertOne({"StudentFirstName":"John", "StudentLastName":"Smith", "StudentAge":24}); 2019-05-08T22:50:42.803+0530 E QUERY [js] WriteError: E11000 duplicate key error collection: sample.keepTwoColumnsUniqueDemo index: StudentFirstName_1_StudentLastName_1 dup key: { : "John", : "Smith" } ... Read More

Use delete operator to unset variable in MongoDB shell. Following is the syntax −delete yourVariableName;Let us now implement the above syntax in order to unset variable in MongoDB shell. First, print the variable name −> customerDetail;This will produce the following output −2019-05-08T22:29:17.361+0530 E QUERY [js] ReferenceError: customerDetail is not defined : @(shell):1:1Now you can set a value in the above variable. Following is the query −> customerDetail={"CustomerFirstName":"Chris"};This will produce the following output −{ "CustomerFirstName" : "Chris" }Following is the query to show the value of a variable −> customerDetail; This will produce the following output −{ "CustomerFirstName" : "Chris" }Following ... Read More

To combine AND & OR in MongoDB, let us first create a collection with documents −>db.combinedAndOrDemo.insertOne({"StudentFirstName":"John", "StudentAge":23, "StudentSkill":"MongoDB"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5cd306dcb64f4b851c3a13e2") } >db.combinedAndOrDemo.insertOne({"StudentFirstName":"Larry", "StudentAge":21, "StudentSkill":"MySQL"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5cd306f3b64f4b851c3a13e3") } >db.combinedAndOrDemo.insertOne({"StudentFirstName":"Sam", "StudentAge":24, "StudentSkill":"SQL Server"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5cd30701b64f4b851c3a13e4") }Following is the query to display all documents from a collection with the help of find() method −> db.combinedAndOrDemo.find().pretty();This will produce the following output −{    "_id" : ObjectId("5cd306dcb64f4b851c3a13e2"),    "StudentFirstName" : "John",    "StudentAge" : 23,    "StudentSkill" : "MongoDB" } {    "_id" : ... Read More

Use DISTINCT for distinct elements and then length to get the size of array −db.yourCollectionName.distinct('yourFieldName').length;Let us first create a collection with documents −> db.countOrSizeDemo.insertOne({"StudentFirstName":"John"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5cd304f5b64f4b851c3a13dc") } > db.countOrSizeDemo.insertOne({"StudentFirstName":"David"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5cd304fab64f4b851c3a13dd") } > db.countOrSizeDemo.insertOne({"StudentFirstName":"David"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5cd304fcb64f4b851c3a13de") } > db.countOrSizeDemo.insertOne({"StudentFirstName":"Carol"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5cd30500b64f4b851c3a13df") } > db.countOrSizeDemo.insertOne({"StudentFirstName":"Sam"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5cd30505b64f4b851c3a13e0") } > db.countOrSizeDemo.insertOne({"StudentFirstName":"John"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5cd3050ab64f4b851c3a13e1") }Following is the query to display all ... Read More

To rename a user, you need to use update() and $set to set the new username. Following is the syntax −db.system.users.update({"user":"yourOldUserName"}, {$set:{"user":"yourNewUserName"}});Firstly, display all the users from the MongoDB database −> use admin; switched to db admin > db.getUsers();This will produce the following output −[    {       "_id" : "admin.Chris",       "user" : "Chris",       "db" : "admin",       "roles" : [          {             "role" : "readWrite",             "db" : "test"          } ... Read More