Data Structure
Networking
RDBMS
Operating System
Java
MS Excel
iOS
HTML
CSS
Android
Python
C Programming
C++
C#
MongoDB
MySQL
Javascript
PHP
To merge multiple documents in MongoDB, use aggregate(). Let us create a collection with documents −> db.demo436.insertOne( ... { ... "_id" : "101", ... "Name": "Chris", ... "details" : [ ... { ... "CountryName" : "US", ... "Age" : 21 ... } ... ], ... "Price" : 50 ... } ... ); { "acknowledged" : true, "insertedId" : "101" } > db.demo436.insertOne( ... ... Read More
To append to array in MongoDB, use $concatArrays. Let us create a collection with documents −> db.demo435.insertOne({"FirstName":["Chris"], "LastName":["Brown"]} ); { "acknowledged" : true, "insertedId" : ObjectId("5e7719b1bbc41e36cc3cae97") } > db.demo435.insertOne({"FirstName":["David"], "LastName":["Miller"]} ); { "acknowledged" : true, "insertedId" : ObjectId("5e7719bdbbc41e36cc3cae98") } > db.demo435.insertOne({"FirstName":["John"], "LastName":["Doe"]} ); { "acknowledged" : true, "insertedId" : ObjectId("5e7719c6bbc41e36cc3cae99") }Display all documents from a collection with the help of find() method −> db.demo435.find().pretty();This will produce the following output −{ "_id" : ObjectId("5e7719b1bbc41e36cc3cae97"), "FirstName" : [ "Chris" ], "LastName" : [ ... Read More
To sum, use aggregate() along with $sum. Let us create a collection with documents −> db.demo434.insertOne({"Name":"Chris", "Score":45}); { "acknowledged" : true, "insertedId" : ObjectId("5e771603bbc41e36cc3cae93") } > db.demo434.insertOne({"Name":"David", "Score":55}); { "acknowledged" : true, "insertedId" : ObjectId("5e77161abbc41e36cc3cae94") } > db.demo434.insertOne({"Name":"Chris", "Score":55}); { "acknowledged" : true, "insertedId" : ObjectId("5e771624bbc41e36cc3cae95") }Display all documents from a collection with the help of find() method −> db.demo434.find();This will produce the following output −{ "_id" : ObjectId("5e771603bbc41e36cc3cae93"), "Name" : "Chris", "Score" : 45 } { "_id" : ObjectId("5e77161abbc41e36cc3cae94"), "Name" : "David", "Score" : 55 } { "_id" : ObjectId("5e771624bbc41e36cc3cae95"), "Name" : "Chris", ... Read More
To filter a query on specific date format, use $dateToString. Let us create a collection with documents −> db.demo433.insertOne({"DueDate":new Date("2019-11-23")}); { "acknowledged" : true, "insertedId" : ObjectId("5e771278bbc41e36cc3cae91") } > db.demo433.insertOne({"DueDate":new Date("2020-01-03")}); { "acknowledged" : true, "insertedId" : ObjectId("5e771290bbc41e36cc3cae92") }Display all documents from a collection with the help of find() method −> db.demo433.find();This will produce the following output −{ "_id" : ObjectId("5e771278bbc41e36cc3cae91"), "DueDate" : ISODate("2019-11-23T00:00:00Z") } { "_id" : ObjectId("5e771290bbc41e36cc3cae92"), "DueDate" : ISODate("2020-01-03T00:00:00Z") }Following is the query to filter a query on specific date format in MongoDB −> db.demo433.aggregate([ ... { $addFields: {stringDate: { $dateToString: { format: ... Read More
For this, you can use aggregate(). We have considered test records as “Value1”, “Value2”, etc. Let us create a collection with documents −> db.demo432.insertOne( ... { ... "_id" : 101, ... "Name" : "David", ... "Value1" : 67, ... "Value2" : 87, ... "Value3" : 78 ... } ... ) { "acknowledged" : true, "insertedId" : 101 } > db.demo432.insertOne( ... { ... "_id" : 102, ... "Name" : "Sam", ... "Value1" : ... Read More
The fastest way is to use replaceOne() in MongoDB. Let us create a collection with documents −> db.demo431.insertOne({"Name":"Chris", "Age":32}); { "acknowledged" : true, "insertedId" : ObjectId("5e770ba6bbc41e36cc3cae89") } > db.demo431.insertOne({"Name":"David", "Age":31}); { "acknowledged" : true, "insertedId" : ObjectId("5e770bacbbc41e36cc3cae8a") } > db.demo431.insertOne({"Name":"John", "Age":24}); { "acknowledged" : true, "insertedId" : ObjectId("5e770bb3bbc41e36cc3cae8b") } > db.demo431.insertOne({"Name":"Bob", "Age":22}); { "acknowledged" : true, "insertedId" : ObjectId("5e770bb8bbc41e36cc3cae8c") }Display all documents from a collection with the help of find() method −> db.demo431.find();This will produce the following output −{ "_id" : ObjectId("5e770ba6bbc41e36cc3cae89"), "Name" : "Chris", "Age" : 32 } { "_id" : ... Read More
Garbage Collection or simply GC is the core part of Memory Management in Java. It can be responsible for cleaning dead objects from memory and reclaiming that space. GC executes cleanup using predefined Garbage Collectors that uses certain algorithms.There are a few important types of Garbage Collectors listed belowSerial GC: A single thread collector and applies to small applications with small data usage. It can be enabled by specifying the command-line option: -XX:+UseSerialGC.Parallel GC: Parallel GC uses multiple threads to perform the garbage collecting process, and it's also known as the throughput collector. It can be enabled by explicitly specifying the option: -XX:+UseParallelGC.G1 Garbage First: G1 (Garbage ... Read More
Let us create a collection with documents −> db.demo430.insertOne( ... { ... "details": [ ... { ... "Name":"Chris" ... } , ... {"Name":"David"}, ... {"Name":"Adam"}, ... {"Name":"Bob"} ... ... ] ... } ... ); { "acknowledged" : true, "insertedId" : ObjectId("5e7702ddbbc41e36cc3cae88") }Display all documents from a collection with the help of find() method −> db.demo430.find();This will produce the following output −{ "_id" : ObjectId("5e7702ddbbc41e36cc3cae88"), "details" : [ { "Name" : "Chris" }, { "Name" : "David" }, { "Name" : "Adam" }, { "Name" : "Bob" } ] }Following is the query to group records −> db.demo430.aggregate([{ "$group" : { "_id" : {"Name" : "$details.Name"}}}]);This will produce the following output −{ "_id" : { "Name" : [ "Chris", "David", "Adam", "Bob" ] } }
For new field, use $addFields in MongoDB. The $addFields is used to add new fields to documents. Let us create a collection with documents −> db.demo429.insertOne( ... { ... "_id": 101, ... "Value": 3, ... "details": [ ... { ... "Age": 29, ... "Value": 3, ... "details1": [ ... 1, ... 2, ... ... Read More
For multiple write operations, use bulkWrite() in MongoDB. Let us create a collection with documents −> db.demo428.insertOne({ "Name" : "Chris", "Age" : 21 }); { "acknowledged" : true, "insertedId" : ObjectId("5e75f428bbc41e36cc3cae83") } > db.demo428.insertOne({ "Name" : "Chris", "Age" : 23 }); { "acknowledged" : true, "insertedId" : ObjectId("5e75f429bbc41e36cc3cae84") } > db.demo428.insertOne({ "Name" : "David", "Age" : 22 }); { "acknowledged" : true, "insertedId" : ObjectId("5e75f42abbc41e36cc3cae85") } > db.demo428.insertOne({ "Name" : "David", "Age" : 21 }); { "acknowledged" : true, "insertedId" : ObjectId("5e75f42abbc41e36cc3cae86") }Display all documents from a collection with the help of ... Read More