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For this, use aggregate() in MongoDB. In that, use $slice to slice array inside array. Let us create a collection with documents −> db.demo111.insertOne( ... { ... "_id" : 101, ... "Name" : "Chris", ... "Details" : [ ... { ... "_id" : 101, ... "Score" : 78, ... "Subjects" : [ ... { ... ... Read More
To update data in MongoDB, use update(). Let us create a collection with documents −> db.demo110.insertOne({"Name":"Chris"}); { "acknowledged" : true, "insertedId" : ObjectId("5e2eeb949fd5fd66da21447b") } > db.demo110.insertOne({"Name":"David"}); { "acknowledged" : true, "insertedId" : ObjectId("5e2eeb9f9fd5fd66da21447c") } > db.demo110.insertOne({"Name":"Bob"}); { "acknowledged" : true, "insertedId" : ObjectId("5e2eeba39fd5fd66da21447d") }Display all documents from a collection with the help of find() method −> db.demo110.find();This will produce the following output −{ "_id" : ObjectId("5e2eeb949fd5fd66da21447b"), "Name" : "Chris" } { "_id" : ObjectId("5e2eeb9f9fd5fd66da21447c"), "Name" : "David" } { "_id" : ObjectId("5e2eeba39fd5fd66da21447d"), "Name" : "Bob" }Following is the query to update data in MongoDB ... Read More
To get the data of the nested JSON object in MongoDB, use findOne(). Let us create a collection with documents −> db.demo109.insertOne( ... { ... "Name" : "Chris", ... "Subjects" : [ ... { ... "Id" : "100", ... "Name":"MySQL", ... "InstructorDetails" : [ ... { ... "Name" : "John" ... ... Read More
Compact Strings have introduced in Java 9 to replace Java 6's Compressed Strings. Its implementation uses byte[] array instead of char[] array and a new field coder has introduced to identify whether it is LATIN1 or UTF16 format while Compressed Strings have introduced in Java 6 that can be used byte[] array for one byte per character, and continued to use char[] array for two bytes per character, previously it can be turned on using -XX: + UseCompressedStrings.Unlike Compressed Strings, Compact Strings do not require un-packing or re-packing. Hence Compact String gives better performance at runtime.Compressed Strings are not enabled by default in Java 6, and need to be ... Read More
To remove duplicate entries by two keys, use aggregate() in MongoDB. Let us create a collection with documents −> db.demo108.insertOne({"Value1":23, "Value2":24}); { "acknowledged" : true, "insertedId" : ObjectId("5e2ee3e49fd5fd66da214477") } > db.demo108.insertOne({"Value1":23, "Value2":25}); { "acknowledged" : true, "insertedId" : ObjectId("5e2ee3f29fd5fd66da214478") } > db.demo108.insertOne({"Value1":23, "Value2":24}); { "acknowledged" : true, "insertedId" : ObjectId("5e2ee3f59fd5fd66da214479") }Display all documents from a collection with the help of find() method −> db.demo108.find();This will produce the following output −{ "_id" : ObjectId("5e2ee3e49fd5fd66da214477"), "Value1" : 23, "Value2" : 24 } { "_id" : ObjectId("5e2ee3f29fd5fd66da214478"), "Value1" : 23, "Value2" : 25 } { "_id" : ... Read More
To use variables, work with var in MongoDB. Let us create a collection with documents −> db.demo107.insertOne({"Name":"Chris"}); { "acknowledged" : true, "insertedId" : ObjectId("5e2ee1b19fd5fd66da214471") } > db.demo107.insertOne({"Name":"Bob"}); { "acknowledged" : true, "insertedId" : ObjectId("5e2ee1b49fd5fd66da214472") } > db.demo107.insertOne({"Name":"David"}); { "acknowledged" : true, "insertedId" : ObjectId("5e2ee1b89fd5fd66da214473") }Display all documents from a collection with the help of find() method −> db.demo107.find();This will produce the following output −{ "_id" : ObjectId("5e2ee1b19fd5fd66da214471"), "Name" : "Chris" } { "_id" : ObjectId("5e2ee1b49fd5fd66da214472"), "Name" : "Bob" } { "_id" : ObjectId("5e2ee1b89fd5fd66da214473"), "Name" : "David" }Following is the query to use variable in ... Read More
You can use bulkWrite(). Let us create a collection with documents −> db.demo105.insertOne( { _id:'101', Name:'Chris', Details:[{ Marks1:60, Marks2:70, Marks3:70 }, { Marks1:70, Marks2:70, Marks3:90 }] } ); { "acknowledged" : true, "insertedId" : "101" }Display all documents from a collection with the help of find() method −> db.demo105.find().pretty();This will produce the following output −{ "_id" : "101", "Name" : "Chris", "Details" : [ { "Marks1" : 60, "Marks2" : 70, "Marks3" : 70 }, { ... Read More
To implement $dateToString on array items, use aggregate() in MongoDB. Let us create a collection with documents −> db.demo104.insertOne( ... { ... ... "AppName" : "Online Book", ... "Details" : [ ... { ... "ClientName" : "Chris", ... "Deadline" : new ISODate("2020-03-10") ... } ... ] ... } ... ); { "acknowledged" : true, "insertedId" : ObjectId("5e2ed7fd9fd5fd66da21446f") }Display all documents from a collection with the help of ... Read More
To query on the last object of an array, use aggregate(). Let us create a collection with documents −> db.demo103.insertOne( { "Details" : [ { "StudentId" : 101, "Details" : "MongoDB" }, {"StudentId" : 102, "Details" : "MySQL" }, { "StudentId" : 103, "Details" : "Java" } ], "Details1" : [ { "StudentId" : 104, "Number" : 3 } ] } ); { "acknowledged" : true, "insertedId" : ObjectId("5e2ed2dd9fd5fd66da21446e") }Display all documents from a collection with the help of find() method −> db.demo103.find();This will produce the following output −{ "_id" : ObjectId("5e2ed2dd9fd5fd66da21446e"), "Details" : ... Read More
For this, create two collections and add some document. After that, use $lookup for match. Let us create a collection with documents −> db.demo101.insertOne( ... { "_id" : "1", "Details" : [ { "PId" : "200" }, { "PId" : "201" }, { "PId" : "201" } ] } ... ) { "acknowledged" : true, "insertedId" : "1" }Display all documents from a collection with the help of find() method −> db.demo101.find();This will produce the following output −{ "_id" : "1", "Details" : [ { "PId" : "200" }, { "PId" : "201" }, { "PId" : "201" } ] ... Read More