For this, use ensureIndex() and set unique:true. Let us create a collection with documents. Here, when we try to inert duplicate item, then a duplicate key error occurs −> db.demo316.ensureIndex({"SubjectName":1}, {unique:true}); {    "createdCollectionAutomatically" : true,    "numIndexesBefore" : 1,    "numIndexesAfter" : 2,    "ok" : 1 } > db.demo316.insertOne({"SubjectName":"MySQL"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e50e378f8647eb59e56205d") } > db.demo316.insertOne({"SubjectName":"MongoDB"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e50e37df8647eb59e56205e") } > db.demo316.insertOne({"SubjectName":"MongoDB"}); 2020-02-22T13:47:05.186+0530 E QUERY [js] WriteError: E11000 duplicate key error collection: test.demo316 index: SubjectName_1 dup key: { : "MongoDB" } : WriteError({    "index" : 0, ... Read More

To update the nested document, use $set. Let us create a collection with documents −> db.demo315.insertOne({ _id :101, ...  details: [ ...     {Name: 'Chris', subjects: [{id:1001, SubjectName:"MySQL"}]} ...  ] ... } ...) { "acknowledged" : true, "insertedId" : 101 }Display all documents from a collection with the help of find() method −> db.demo315.find().pretty();This will produce the following output −{    "_id" : 101,    "details" : [       {          "Name" : "Chris",          "subjects" : [             {             ... Read More

You can use positional $ operator. Let us first create a collection with documents −> db.demo22.insertOne( ...    { ...       ProductId:101, ... ...       ProductDetails: ...       [ ...          { ...             ProductFirstPrice: '35', ...             ProductSecondPrice: '75' ...          }, ...          { ...             ProductFirstPrice: '', ...             ProductSecondPrice:'' ...          }, ...          { ... Read More

To update child objects, use $set in MongoDB. Let us first create a collection with documents −>db.demo21.insertOne({"StudentId":"STU-101", "StudentDetails":{"StudentName":"Chris", "StudentAge":21}}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e14be8922d07d3b95082e6f") }Display all documents from a collection with the help of find() method −> db.demo21.find().pretty();This will produce the following output −{    "_id" : ObjectId("5e14be8922d07d3b95082e6f"),    "StudentId" : "STU-101",    "StudentDetails" : {       "StudentName" : "Chris",       "StudentAge" : 21    } }Following is the query to update child objects in MongoDB −> db.demo21.update({"StudentId":'STU-101'}, {$set:{'StudentDetails.StudentName':'Robert'}}); WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })Display all documents ... Read More

To shutdown MongoDB, you need to use shutdownServer() as in the below syntax −db.shutdownServer();First you need to switch to admin as shown below −use admin;Here, we switched to admin −> use admin; switched to db adminFollowing is the query to shutdown server −> db.shutdownServer();This will produce the following output −server should be down... 2020-01-07T22:40:31.295+0530 I NETWORK [js] trying reconnect to 127.0.0.1:27017 failed 2020-01-07T22:40:32.326+0530 I NETWORK [js] reconnect 127.0.0.1:27017 failed failed

To get the number of open connections, use serverStatus() in MongoDB. Following is the query −> db.serverStatus();This will produce the following output −{    "host" : "DESKTOP-QN2RB3H",    "version" : "4.0.5",    "process" : "mongod",    "pid" : NumberLong(10540),    "uptime" : 74156,    "uptimeMillis" : NumberLong(74156688),    "uptimeEstimate" : NumberLong(74156),    "localTime" : ISODate("2020-01-07T15:09:18.366Z"),    "asserts" : {       "regular" : 0,       "warning" : 0,       "msg" : 0,       "user" : 1,       "rollovers" : 0    },    "connections" : {       "current" : ... Read More

You can use $unset. Let us first create a collection with documents −> db.demo20.insertOne( ...    { ... ...       "ListOfEmployee" : [ ...          { ...             "EmployeeName1" : "John" ...          }, ...          { ...             "EmployeeName2" : "Carol" ...          } ...       ], ...       "EmployeeName2" : [] ...    } ... ); {    "acknowledged" : true,    "insertedId" : ObjectId("5e138c3555d0fc6657d21f12") }Following is the query to ... Read More

To filter records using Regular Expression in MongoDB, use $regex. Let us first create a collection with documents −> db.demo19.insertOne({"Values":"4321GH"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e1389b955d0fc6657d21f0f") } > db.demo19.insertOne({"Values":"12321_Carol"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e1389c755d0fc6657d21f10") } > db.demo19.insertOne({"Values":"8765Mike"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e1389d355d0fc6657d21f11") }Following is the query to display all documents from a collection with the help of find() method −> db.demo19.find();This will produce the following output −{ "_id" : ObjectId("5e1389b955d0fc6657d21f0f"), "Values" : "4321GH" } { "_id" : ObjectId("5e1389c755d0fc6657d21f10"), "Values" : "12321_Carol" } { "_id" : ObjectId("5e1389d355d0fc6657d21f11"), "Values" : "8765Mike" ... Read More

To convert a field to an array, use UPDATE operation inside forEach(). Let us first create a collection with documents −> db.demo18.insertOne({"StudentName":"John"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e1387fc55d0fc6657d21f0e") }Following is the query to display all documents from a collection with the help of find() method −> db.demo18.find();This will produce the following output −{ "_id" : ObjectId("5e1387fc55d0fc6657d21f0e"), "StudentName" : "John" }Here is the query to convert a field to an array using update operation −> db.demo18.find().forEach(function(myDocument) { ...    db.demo18.update( ...       { _id: myDocument._id }, ...       { "$set": { "StudentName": [myDocument.StudentName] } ... Read More

For this, use $all, that would find documents containing all of the elements in an array like "keys". Let us first create a collection with documents −> db.demo17.insertOne({"ListOfSubject":["MySQL", "MongoDB", "Java"]}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e13847255d0fc6657d21f0a") } > db.demo17.insertOne({"ListOfSubject":["C", "Python", "Java"]}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e13847e55d0fc6657d21f0b") } > db.demo17.insertOne({"ListOfSubject":["C++", "MongoDB", "PL/SQL"]}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e13849255d0fc6657d21f0c") }Following is the query to display all documents from a collection with the help of find() method −> db.demo17.find();This will produce the following output −{ "_id" : ObjectId("5e13847255d0fc6657d21f0a"), "ListOfSubject" : [ "MySQL", "MongoDB", ... Read More