Article Categories
- All Categories
-
Data Structure
-
Networking
-
RDBMS
-
Operating System
-
Java
-
MS Excel
-
iOS
-
HTML
-
CSS
-
Android
-
Python
-
C Programming
-
C++
-
C#
-
MongoDB
-
MySQL
-
Javascript
-
PHP
Articles on Trending Technologies
Technical articles with clear explanations and examples
How to get the child of a MongoDB collection by the key?
To get the child of a collection in MongoDB, use find(). Let us create a collection with documents −> db.demo305.insertOne( ... { ... _id: 101, ... FirstName : 'Chris', ... details : { ... "0":"102", ... "1":"10001" ... } ... } ...); { "acknowledged" : true, "insertedId" : 101 } > db.demo305.insertOne( ... { ... _id: 102, ... FirstName : 'David', ... details : { ... "0":"103", ... "1":"10002" ... } ... } ...); { "acknowledged" : true, "insertedId" : 102 }Display all documents from a collection with the help of find() method −> db.demo305.find();This will produce the following output −{ "_id" : 101, "FirstName" : "Chris", "details" : { "0" : "102", "1" : "10001" } } { "_id" : 102, "FirstName" : "David", "details" : { "0" : "103", "1" : "10002" } }Following is the query to get the child of a MongoDB collection by the key −> db.demo305.find({_id:102},{'details.0':1});This will produce the following output −{ "_id" : 102, "details" : { "0" : "103" } }
Read MoreFind values with OR operator in MongoDB and format the result.?
Use $or operator to fetch values and to format the result, use “pretty()”. Let us create a collection with documents −> db.demo304.insertOne({"StudentName":"Chris", "StudentAge":23}); { "acknowledged" : true, "insertedId" : ObjectId("5e4ea3ccf8647eb59e562034") } > db.demo304.insertOne({"StudentName":"David", "StudentAge":22}); { "acknowledged" : true, "insertedId" : ObjectId("5e4ea3d7f8647eb59e562035") } > db.demo304.insertOne({"StudentName":"Mike", "StudentAge":24}); { "acknowledged" : true, "insertedId" : ObjectId("5e4ea3e2f8647eb59e562036") } > db.demo304.insertOne({"StudentName":"Carol", "StudentAge":22}); { "acknowledged" : true, "insertedId" : ObjectId("5e4ea3eef8647eb59e562037") }Display all documents from a collection with the help of find() method −> db.demo304.find();This will produce the following output −{ "_id" : ObjectId("5e4ea3ccf8647eb59e562034"), "StudentName" : "Chris", "StudentAge" : 23 ...
Read MoreMongoDB query to get distinct FirstName values from documents
For distinct values, use distinct(). Let us create a collection with documents −> db.demo303.insertOne({FirstName:"Chris", LastName:"Brown"}); { "acknowledged" : true, "insertedId" : ObjectId("5e4ea0f6f8647eb59e56202f") } > db.demo303.insertOne({FirstName:"John", LastName:"Doe"}); { "acknowledged" : true, "insertedId" : ObjectId("5e4ea104f8647eb59e562030") } > db.demo303.insertOne({FirstName:"Chris", LastName:"Smith"}); { "acknowledged" : true, "insertedId" : ObjectId("5e4ea10df8647eb59e562031") } > db.demo303.insertOne({FirstName:"John", LastName:"Smith"}); { "acknowledged" : true, "insertedId" : ObjectId("5e4ea121f8647eb59e562032") } > db.demo303.insertOne({FirstName:"David", LastName:"Miller"}); { "acknowledged" : true, "insertedId" : ObjectId("5e4ea136f8647eb59e562033") }Display all documents from a collection with the help of find() method −> db.demo303.find().pretty();This will produce the following output −{ "_id" : ObjectId("5e4ea0f6f8647eb59e56202f"), ...
Read MoreField selection within MongoDB query using dot notation?
For this, use dot notation for field selection in MongoDB find(). Let us create a collection with documents −> db.demo302.insertOne({"Id":101, "details":[{"Name":"Chris", Age:21, "Subject":"MySQL"}]}); { "acknowledged" : true, "insertedId" : ObjectId("5e4d746f5d93261e4bc9ea52") } > db.demo302.insertOne({"Id":102, "details":[{"Name":"Bob", Age:23, "Subject":"MongoDB"}]}); { "acknowledged" : true, "insertedId" : ObjectId("5e4d74815d93261e4bc9ea53") } > db.demo302.insertOne({"Id":103, "details":[{"Name":"David", Age:20, "Subject":"Java"}]}); { "acknowledged" : true, "insertedId" : ObjectId("5e4d74955d93261e4bc9ea54") }Display all documents from a collection with the help of find() method −> db.demo302.find();This will produce the following output −{ "_id" : ObjectId("5e4d746f5d93261e4bc9ea52"), "Id" : 101, "details" : [ { "Name" : "Chris", "Age" : 21, "Subject" : ...
Read MoreMongoDB query to change order of array elements?
Use swap concept to change the order of array elements. Let us create a collection with documents −> db.demo301.insertOne({"Name":["Chris", "David", "Bob"]}); { "acknowledged" : true, "insertedId" : ObjectId("5e4d6ff55d93261e4bc9ea51") }Display all documents from a collection with the help of find() method −> db.demo301.find();This will produce the following output −{ "_id" : ObjectId("5e4d6ff55d93261e4bc9ea51"), "Name" : [ "Chris", "David", "Bob" ] }Following is the query to change the order of array elements −> db.demo301.find({}, { Name : 1 }).forEach(function(n) { ... var t = n.Name[0]; ... n.Name[0] = n.Name[1]; ... n.Name[1] = t; ... db.demo301.update({ _id: n._id ...
Read MoreMongoDB query to access an object in an array
To access an object in an array, use dot notation. Let us create a collection with documents −> db.demo299.insertOne( ... { ... "id":100, ... "Name":"Robert", ... "details":[ ... { ... "SubjectName":["C++", "Python"] ... }, ... { ... "SubjectName":["Spring", "Hibernate"] ... } ... ] ... } ...); { "acknowledged" : true, "insertedId" : ObjectId("5e4d685a5d93261e4bc9ea4b") } > > > db.demo299.insertOne( ... { ... ...
Read MoreMongoDB transaction & indexes for duplicate values
Use ensureIndex() and set unique:1 inside the array. Let us create a collection with documents −> db.demo298.save({Name: 'Chris', Marks: [46, 79] }); WriteResult({ "nInserted" : 1 }) > db.demo298.save({Name: 'David', Marks: [67, 88] }); WriteResult({ "nInserted" : 1 }) > db.demo298.ensureIndex({ Marks: 1 }, {unique: 1}); { "createdCollectionAutomatically" : false, "numIndexesBefore" : 1, "numIndexesAfter" : 2, "ok" : 1 } > db.demo298.save({Name: 'Mike', Marks: [88, 98] }); WriteResult({ "nInserted" : 0, "writeError" : { "code" : 11000, "errmsg" : "E11000 duplicate key error collection: test.demo298 index: Marks_1 dup ...
Read MoreMongoDB query to insert but limit the total records
To insert and limit the total records while inserting, use capped:true and set the size and max values.Let us create a collection with documents wherein we have set capped:true and size to 4 −> db.createCollection("demo297", {capped:true, size:4, max:4}); { "ok" : 1 } > db.demo297.insertOne({"Name":"Chris"}); { "acknowledged" : true, "insertedId" : ObjectId("5e4d54385d93261e4bc9ea43") } > db.demo297.insertOne({"Name":"Bob"}); { "acknowledged" : true, "insertedId" : ObjectId("5e4d543e5d93261e4bc9ea44") } > db.demo297.insertOne({"Name":"Mike"}); { "acknowledged" : true, "insertedId" : ObjectId("5e4d543e5d93261e4bc9ea45") } > db.demo297.insertOne({"Name":"Sam"}); { "acknowledged" : true, "insertedId" : ObjectId("5e4d543f5d93261e4bc9ea46") } > db.demo297.insertOne({"Name":"John"}); { "acknowledged" : true, "insertedId" : ObjectId("5e4d54405d93261e4bc9ea47") ...
Read MoreNative Querying MongoDB inside array and get the count
To query inside array and check for existence to get the count, use $exists. Let us create a collection with documents −> db.demo296.insertOne( ... { ... "id":101, ... "Name":"Chris", ... "details":[ ... { ... SubjectId:[101, 103], ... "SubjectName":["MySQL", "MongoDB"] ... }, ... { ... SubjectId:[102, 104], ... "SubjectName":["Java", "C"] ... } ... ] ... ...
Read MoreQuerying object's field array values in MongoDB?
Query object’s field array value using arrayFieldName along with value. Let us create a collection with documents −> db.demo295.insertOne({"status":["Active", "Inactive"]}); { "acknowledged" : true, "insertedId" : ObjectId("5e4d4ea65d93261e4bc9ea39") } > db.demo295.insertOne({"status":["Yes", "No"]}); { "acknowledged" : true, "insertedId" : ObjectId("5e4d4eb15d93261e4bc9ea3a") }Display all documents from a collection with the help of find() method −> db.demo295.find().pretty();This will produce the following output −{ "_id" : ObjectId("5e4d4ea65d93261e4bc9ea39"), "status" : [ "Active", "Inactive" ] } { "_id" : ObjectId("5e4d4eb15d93261e4bc9ea3a"), "status" : [ "Yes", "No" ] ...
Read More