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Articles on Trending Technologies
Technical articles with clear explanations and examples
MongoDB projection result as an array of selected items?
Let us create a collection with documents −> db.demo151.insertOne({"ListOfNames":["Chris", "David", "Mike"]}); { "acknowledged" : true, "insertedId" : ObjectId("5e3513b6fdf09dd6d08539da") } > db.demo151.insertOne({"ListOfNames":["Mike", "Bob"]}); { "acknowledged" : true, "insertedId" : ObjectId("5e3513c4fdf09dd6d08539db") } > db.demo151.insertOne({"ListOfNames":["John", "David", "Chris"]}); { "acknowledged" : true, "insertedId" : ObjectId("5e3513dcfdf09dd6d08539dc") }Display all documents from a collection with the help of find() method −> db.demo151.find();This will produce the following output −{ "_id" : ObjectId("5e3513b6fdf09dd6d08539da"), "ListOfNames" : [ "Chris", "David", "Mike" ] } { "_id" : ObjectId("5e3513c4fdf09dd6d08539db"), "ListOfNames" : [ "Mike", "Bob" ] } { "_id" : ObjectId("5e3513dcfdf09dd6d08539dc"), "ListOfNames" : [ "John", "David", "Chris" ] ...
Read MoreConditional update depending on field matched in MongoDB
For conditional update, use update() and set new value using $set. Let us create a collection with documents −> db.demo150.insertOne({"StudentId":101, "StudentName":"Chris", "StudentMarks":35}); { "acknowledged" : true, "insertedId" : ObjectId("5e350dcdfdf09dd6d08539d3") } > db.demo150.insertOne({"StudentId":102, "StudentName":"Chris", "StudentMarks":55}); { "acknowledged" : true, "insertedId" : ObjectId("5e350dcefdf09dd6d08539d4") } > db.demo150.insertOne({"StudentId":103, "StudentName":"David", "StudentMarks":34}); { "acknowledged" : true, "insertedId" : ObjectId("5e350dcffdf09dd6d08539d5") } > db.demo150.insertOne({"StudentId":104, "StudentName":"Chris", "StudentMarks":38}); { "acknowledged" : true, "insertedId" : ObjectId("5e350dd0fdf09dd6d08539d6") }Display all documents from a collection with the help of find() method −> db.demo150.find();This will produce the following output −{ "_id" : ObjectId("5e350dcdfdf09dd6d08539d3"), "StudentId" : 101, "StudentName" ...
Read MoreWhat are the core library changes in Process API in Java 9?
In Java 9, one can retrieve the PID of the process through a native call and can be achievable through the ProcessHandle. We can also retrieve information about the currently running Java Process (JVM) and Info (inner class of ProcessHandle) class that contains details about the process. We can also return a snapshot of all currently running processes in the system.Exampleimport java.lang.ProcessHandle.Info; public class ProcessAPIChanges { public void detailedAPIInfo(ProcessHandle processHandle) { Info processInfo = processHandle.info(); System.out.println("Detailed Process Info is Provided Below: "); System.out.println("[Executable Name] " + processInfo.command().get()); System.out.println("[User Name] " + ...
Read MoreSemaphore in C#
The semaphore class lets you set a limit on the number of threads that have access to a critical section. The class is used to control access to a pool of resources. System.Threading.Semaphore is the namespace for Semaphore because it has all the methods and properties required to implement Semaphore.For using a semaphore in C#, you just need to instantiate an instance of a Semaphore object. It has minimum of two arguments −Reference−MSDNSr.No.Constructor & Description1Semaphore(Int32, Int32)Initializes a new instance of the Semaphore class, specifying the initial number of entries and the maximum number of concurrent entries.2Semaphore(Int32, Int32, String) −Initializes a ...
Read MoreWhich modifiers can't allow in the top-level declaration in JShell in Java 9?
JShell is an interactive tool for learning the Java language and prototyping Java code. It is a REPL (Read-Evaluate-Print-Loop) that evaluates declarations, statements, and expressions once entered and immediately prints the results in JShell. This tool runs from the command-line prompt.The modifiers like public, protected, private, static, and final have not allowed on top-level declarations and can be ignored with a warning. The keywords like synchronized, native, abstract, and default top-level methods have not allowed and can be errors.In the below code snippets, we have created both final and static variables. It prints out a warning message to the user that "Modifier 'final' or 'static' not permitted ...
Read MoreMongoDB $elemMatch to match document
Let us create a collection with documents −> db.demo313.insertOne({"_id":100, "details":[{"Name":"Chris", "Age":24}]}); { "acknowledged" : true, "insertedId" : 100 } > db.demo313.insertOne({"_id":101, "details":[{"Name":"David", "Age":22}]}); { "acknowledged" : true, "insertedId" : 101 } > db.demo313.insertOne({"_id":102, "details":[{"Name":"Mike", "Age":25}]}); { "acknowledged" : true, "insertedId" : 102 }Display all documents from a collection with the help of find() method −> db.demo313.find();This will produce the following output −{ "_id" : 100, "details" : [ { "Name" : "Chris", "Age" : 24 } ] } { "_id" : 101, "details" : [ { "Name" : "David", "Age" : 22 } ] } { "_id" : 102, "details" ...
Read MoreMongoDB - update partial number of documents?
To update partial number of documents, set multi to true. Let us create a collection with documents −> db.demo312.insertOne({"FirstName":"Robert"}); { "acknowledged" : true, "insertedId" : ObjectId("5e50ce16f8647eb59e56204a") } > db.demo312.insertOne({"FirstName":"Bob"}); { "acknowledged" : true, "insertedId" : ObjectId("5e50ce19f8647eb59e56204b") } > db.demo312.insertOne({"FirstName":"Robert"}); { "acknowledged" : true, "insertedId" : ObjectId("5e50ce1cf8647eb59e56204c") } > db.demo312.insertOne({"FirstName":"David"}); { "acknowledged" : true, "insertedId" : ObjectId("5e50ce20f8647eb59e56204d") } > db.demo312.insertOne({"FirstName":"Robert"}); { "acknowledged" : true, "insertedId" : ObjectId("5e50ce22f8647eb59e56204e") }Display all documents from a collection with the help of find() method −> db.demo312.find();This will produce the following output −{ "_id" : ObjectId("5e50ce16f8647eb59e56204a"), "FirstName" ...
Read MoreGet the count of a specific value in MongoDB quickly
For faster queries, create an index. To get the count, use count(). Let us create a collection with documents −> db.demo311.ensureIndex({"Name":1}); { "createdCollectionAutomatically" : true, "numIndexesBefore" : 1, "numIndexesAfter" : 2, "ok" : 1 } > db.demo311.insertOne({"Name":"Chris"}); { "acknowledged" : true, "insertedId" : ObjectId("5e50cd01f8647eb59e562044") } > db.demo311.insertOne({"Name":"David"}); { "acknowledged" : true, "insertedId" : ObjectId("5e50cd05f8647eb59e562045") } > db.demo311.insertOne({"Name":"David"}); { "acknowledged" : true, "insertedId" : ObjectId("5e50cd06f8647eb59e562046") } > db.demo311.insertOne({"Name":"Chris"}); { "acknowledged" : true, "insertedId" : ObjectId("5e50cd0af8647eb59e562047") } > db.demo311.insertOne({"Name":"Bob"}); { "acknowledged" : true, "insertedId" : ObjectId("5e50cd0df8647eb59e562048") } > db.demo311.insertOne({"Name":"Chris"}); { ...
Read MoreRetrieving a Subset of Fields from MongoDB
To retried a subset of fields, use dot notation in find(). Let us create a collection with documents −> db.demo307.insertOne({ ... "CleintId":101, ... "ClientDetails":{"ClientFirstName":"Chris", "Age":34}, ... "ClientCountryName":"US" ...} ...); { "acknowledged" : true, "insertedId" : ObjectId("5e4eab88f8647eb59e56203c") } > db.demo307.insertOne({ ... "CleintId":102, ... "ClientDetails":{"ClientFirstName":"David", "Age":31}, ... "ClientCountryName":"UK" ...} ...); { "acknowledged" : true, "insertedId" : ObjectId("5e4eab97f8647eb59e56203d") }Display all documents from a collection with the help of find() method −> db.demo307.find();This will produce the following output −{ "_id" : ObjectId("5e4eab88f8647eb59e56203c"), "CleintId" : 101, "ClientDetails" : { "ClientFirstName" : "Chris", "Age" : 34 ...
Read MoreFetching all documents from MongoDB Collection in a beautified form
To fetch documents, use find() in MongoDB. With that, to format the resultant documents, use pretty().Let us create a collection with documents −> db.demo306.insertOne({"Name":"Robert", "Age":21}); { "acknowledged" : true, "insertedId" : ObjectId("5e4ea7c6f8647eb59e562038") } > db.demo306.insertOne({"Name":"David", "Age":23}); { "acknowledged" : true, "insertedId" : ObjectId("5e4ea7cdf8647eb59e562039") } > db.demo306.insertOne({"Name":"Mike", "Age":25}); { "acknowledged" : true, "insertedId" : ObjectId("5e4ea7d4f8647eb59e56203a") } > db.demo306.insertOne({"Name":"Carol", "Age":26}); { "acknowledged" : true, "insertedId" : ObjectId("5e4ea7dcf8647eb59e56203b") }Display all documents from a collection with the help of find() method −> db.demo306.find().pretty();This will produce the following output −{ "_id" : ObjectId("5e4ea7c6f8647eb59e562038"), "Name" : ...
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