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Articles on Trending Technologies
Technical articles with clear explanations and examples
Is there a MongoDB query to concatenate deep sub-lists?
Concatenate deep sub-lists using aggregate() along with $unwind. Let us create a collection with documents −> db.demo70.insertOne( ... { ... ... "first" : [ ... { ... "details" : { ... "second" : [ ... { ... "StudentDetails" : { ... "Score" : 10 ... ...
Read MoreMongoDB, finding all documents where property id equals to record id?
For this, use $where and compare with ==. Let us create a collection with documents −> db.demo69.insertOne( ... { ... "_id" : ObjectId("507c7f79bcf86cd7994f6c0e"), ... "Details" : { ... ... "id" : ObjectId("507c7f79bcf86cd7994f6c0e") ... } ... } ... ); { "acknowledged" : true, "insertedId" : ObjectId("507c7f79bcf86cd7994f6c0e") } > db.demo69.insertOne( ... { ... "_id" : ObjectId("507c7f79bcf86cd7994f6c0f"), "Details" : { ... "id" :ObjectId("507c7f79bcf86cd7994f6c0a") ... } ... } ... ); { "acknowledged" : true, "insertedId" : ObjectId("507c7f79bcf86cd7994f6c0f") }Display all documents from a collection with the help of find() method −> db.demo69.find();This will produce ...
Read MoreMongoDB aggregate query to sort
To sort, use $match along with aggregate. Let us create a collection with documents −> db.demo67.insertOne({"StudentAge":23}); { "acknowledged" : true, "insertedId" : ObjectId("5e289edf602d9a2ff1828ed8") } > db.demo67.insertOne({"StudentAge":21}); { "acknowledged" : true, "insertedId" : ObjectId("5e289ee1602d9a2ff1828ed9") } > db.demo67.insertOne({"StudentAge":24}); { "acknowledged" : true, "insertedId" : ObjectId("5e289ee3602d9a2ff1828eda") }Display all documents from a collection with the help of find() method −> db.demo67.find();This will produce the following output −{ "_id" : ObjectId("5e289edf602d9a2ff1828ed8"), "StudentAge" : 23 } { "_id" : ObjectId("5e289ee1602d9a2ff1828ed9"), "StudentAge" : 21 } { "_id" : ObjectId("5e289ee3602d9a2ff1828eda"), "StudentAge" : 24 }Following is the query to sort with aggregate in ...
Read MoreHow to get the index of an array element in older versions on MongoDB?
To get index of an array element, use $indexOfArray. Let us create a collection with documents −> db.demo65.insertOne({"ListOfValues":[10, 20, 30]}); { "acknowledged" : true, "insertedId" : ObjectId("5e28990ecfb11e5c34d89938") } > db.demo65.insertOne({"ListOfValues":[50, 60, 70, 100]}); { "acknowledged" : true, "insertedId" : ObjectId("5e28991ecfb11e5c34d89939") } > db.demo65.insertOne({"ListOfValues":[30, 40, 89, 91, 98]}); { "acknowledged" : true, "insertedId" : ObjectId("5e28992bcfb11e5c34d8993a") }Display all documents from a collection with the help of find() method −> db.demo65.find();This will produce the following output −{ "_id" : ObjectId("5e28990ecfb11e5c34d89938"), "ListOfValues" : [ 10, 20, 30 ] } { "_id" : ObjectId("5e28991ecfb11e5c34d89939"), "ListOfValues" : [ 50, 60, ...
Read MoreWhat is the importance of REPL in Java 9?
REPL stands for Read-Eval-Print-Loop. It is a shell where the user types an expression, it's evaluated, and the result returned to the user. The main purpose of using REPL is to interact quickly with Java programs without creating a java file, compile it, and run it. JShell is very useful for the developers and allows us to learn the Java language.Below are some of the features of REPLIt’s built-in in Java 9.We can test any Java expression without a class file, compiling and running it.It autocompletes the methods, just typing the TAB key, as in your editor.We can define methods, and ...
Read MoreHow to get a stream from Optional class in Java 9?
The Optional class provides a container that may or may not contain a non-null value. It has been introduced in Java 8 to reduce the number of places in the code where a NullPointerException has generated. Java 9 added three methods: ifPresentOrElse(), or(), and stream(), which helps us deal with default values.In the below example, we can get a stream from Optional class using Person classExampleimport java.util.Optional; import java.util.stream.Stream; public class OptionalTest { public static void main(String args[]) { getPerson().stream() .map(Person::getName) ...
Read MoreMongoDB aggregation to sum product price with similar IDs
You need to use $group to group documents with specified _id expression. Let us first create a collection with documents −> db.aggreagateDemo.insertOne({"Product_Id":1, "ProductPrice":50}); { "acknowledged" : true, "insertedId" : ObjectId("5e06d3c025ddae1f53b621d9") } > db.aggreagateDemo.insertOne({"Product_Id":2, "ProductPrice":100}); { "acknowledged" : true, "insertedId" : ObjectId("5e06d3c625ddae1f53b621da") } > db.aggreagateDemo.insertOne({"Product_Id":2, "ProductPrice":500}); { "acknowledged" : true, "insertedId" : ObjectId("5e06d3cb25ddae1f53b621db") } > db.aggreagateDemo.insertOne({"Product_Id":1, "ProductPrice":150}); { "acknowledged" : true, "insertedId" : ObjectId("5e06d3d125ddae1f53b621dc") }Following is the query to display all documents from a collection with the help of find() method −> db.aggreagateDemo.find().pretty();This will produce the following output −{ "_id" : ObjectId("5e06d3c025ddae1f53b621d9"), ...
Read MoreHow to properly use 'exist' function in MongoDB like in SQL?\\n
To check for existence of a record, use findOne() in MongoDB. Let us first create a collection with documents −> db.existsAlternateDemo.insertOne({"StudentName":"Chris"}); { "acknowledged" : true, "insertedId" : ObjectId("5e06d23f9e4dae213890ac5c") } > db.existsAlternateDemo.insertOne({"StudentName":"Chris", "StudentAge":21}); { "acknowledged" : true, "insertedId" : ObjectId("5e06d2559e4dae213890ac5d") } >db.existsAlternateDemo.insertOne({"StudentName":"Chris", "StudentAge":22, "StudentCountryName":"US"}); { "acknowledged" : true, "insertedId" : ObjectId("5e06d2689e4dae213890ac5e") }Following is the query to display all documents from a collection with the help of find() method −> db.existsAlternateDemo.find();This will produce the following output −{ "_id" : ObjectId("5e06d23f9e4dae213890ac5c"), "StudentName" : "Chris" } { "_id" : ObjectId("5e06d2559e4dae213890ac5d"), "StudentName" : "Chris", "StudentAge" : 21 } { ...
Read MoreInsert in MongoDB without duplicates
To insert records in MongoDB and avoid duplicates, use “unique:true”. Let us first create a collection with documents.Here, we are trying to add duplicate records −> db.insertWithoutDuplicateDemo.createIndex({"StudentFirstName":1}, { unique: true } ); { "createdCollectionAutomatically" : true, "numIndexesBefore" : 1, "numIndexesAfter" : 2, "ok" : 1 } > db.insertWithoutDuplicateDemo.insert({"StudentFirstName":"Chris"}, { upsert: true }); WriteResult({ "nInserted" : 1 }) > db.insertWithoutDuplicateDemo.insert({"StudentFirstName":"David"}, { upsert: true }); WriteResult({ "nInserted" : 1 }) > db.insertWithoutDuplicateDemo.insert({"StudentFirstName":"Chris"}, { upsert: true }); WriteResult({ "nInserted" : 0, "writeError" : { "code" : 11000, "errmsg" : "E11000 duplicate ...
Read MoreApply a condition inside subset in MongoDB Aggregation?
To apply a condition, use $setIsSubset. Let us first create a collection with documents −> db.subsetDemo.insertOne({"StudentName":"Chris", "StudentFavouriteSubject":["Java", "Python"]}); { "acknowledged" : true, "insertedId" : ObjectId("5e063e49150ee0e76c06a052") } > db.subsetDemo.insertOne({"StudentName":"Chris", "StudentFavouriteSubject":["Java", "Python", "MySQL"]}); { "acknowledged" : true, "insertedId" : ObjectId("5e063e4f150ee0e76c06a053") }Following is the query to display all documents from a collection with the help of find() method −> db.subsetDemo.find().pretty();This will produce the following output −{ "_id" : ObjectId("5e063e49150ee0e76c06a052"), "StudentName" : "Chris", "StudentFavouriteSubject" : [ "Java", "Python" ] } { "_id" : ObjectId("5e063e4f150ee0e76c06a053"), "StudentName" : "Chris", ...
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