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To get values greater than a specific value, use $gt along with find(). Let us create a collection with documents −> db.demo317.insertOne( ... {'id':101, ... 'details':[{'Score':78, Name:"Chris"}, ... {'Score':88, Name:"David"} ... ] ... } ... ); { "acknowledged" : true, "insertedId" : ObjectId("5e50e69cf8647eb59e562060") } > db.demo317.insertOne( ... {'id':102, ... 'details':[{'Score':90, Name:"Chris"}, ... {'Score':91, Name:"David"} ... ] ... } ... ); { "acknowledged" : true, "insertedId" : ObjectId("5e50e6adf8647eb59e562061") }Display all documents from a collection with the ... Read More
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
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
In Java 9, a new feature "multi-release jar format" has been introduced where jar format enhanced with different versions of Java class or resources that can be maintained and used as per the platform. A jar command can be used to create a multi-release jar that contains two versions of the same class compiled for both Java 8 and Java 9 versions with a warning message, telling that both classes are identical.C:\Users\User\tutorialspoint>jar --create --file MR.jar -C sampleproject-base demo --release 9 -C sampleproject-9 demo Warning: entry META-INF/versions/9/demo/SampleClass.class contains a class thatis identical to an entry already in the jarThe " --release 9" option can tell jar ... Read More
JShell is the first REPL(Read-Evaluate-Print-Loop) interactive tool that has been introduced as a part of Java 9. It evaluates declarations, statements, and expressions as entered and immediately shows the results, and it runs from the command-line prompt.Palindrome string is a string where it remains the same when reversed or word spelled the same way in both forward and backward directions.In the below example, we can able to check whether the given string is palindrome or not in the JShell tool.C:\Users\User>jshell | Welcome to JShell -- Version 9.0.4 | For an introduction type: /help intro jshell> String str="LEVEL"; str ==> "LEVEL" jshell> ... 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
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