Data Structure
Networking
RDBMS
Operating System
Java
MS Excel
iOS
HTML
CSS
Android
Python
C Programming
C++
C#
MongoDB
MySQL
Javascript
PHP
The $ifNull evaluates an expression and returns the value of the expression if the expression evaluates to a non-null value.Let us first create a collection with documents −> db.demo372.insertOne({"FirstName":"Chris"}); { "acknowledged" : true, "insertedId" : ObjectId("5e591aea2ae06a1609a00af6") } > db.demo372.insertOne({"FirstName":null}); { "acknowledged" : true, "insertedId" : ObjectId("5e591aef2ae06a1609a00af7") } > db.demo372.insertOne({"FirstName":"David"}); { "acknowledged" : true, "insertedId" : ObjectId("5e591af42ae06a1609a00af8") } > db.demo372.insertOne({"FirstName":null}); { "acknowledged" : true, "insertedId" : ObjectId("5e591afb2ae06a1609a00af9") }Display all documents from a collection with the help of find() method −> db.demo372.find();This will produce the following output −{ "_id" : ObjectId("5e591aea2ae06a1609a00af6"), "FirstName" : "Chris" ... Read More
To change the primary key, you need to first delete it. Use forEach() along with delete to remove and then get a new primary key. Let us create a collection with documents −> db.demo41.insertOne({"StudentName":"Carol"}); { "acknowledged" : true, "insertedId" : ObjectId("5e25ce4acfb11e5c34d898e3") }Display all documents from a collection with the help of find() method −> db.demo41.find();This will produce the following output −{ "_id" : ObjectId("5e25ce4acfb11e5c34d898e3"), "StudentName" : "Carol" }Here is the query to change the primary key on a MongoDB collection −> var next = db.demo41.find() > > next.forEach(function(s) { ... var prevId=s._id; ... delete s._id; ... ... Read More
Let us first create a collection with documents −> db.demo371.insertOne({"Name":"David", "CountryName":"US"}); { "acknowledged" : true, "insertedId" : ObjectId("5e57f6982ae06a1609a00af2") } > db.demo371.insertOne({"Name":"John", "CountryName":"UK"}); { "acknowledged" : true, "insertedId" : ObjectId("5e57f69e2ae06a1609a00af3") } > db.demo371.insertOne({"Name":"Bob", "CountryName":"AUS"}); { "acknowledged" : true, "insertedId" : ObjectId("5e57f6a42ae06a1609a00af4") } > db.demo371.insertOne({"Name":"Mike", "CountryName":"US"}); { "acknowledged" : true, "insertedId" : ObjectId("5e57f6ba2ae06a1609a00af5") }Display all documents from a collection with the help of find() method −> db.demo371.find();This will produce the following output −{ "_id" : ObjectId("5e57f6982ae06a1609a00af2"), "Name" : "David", "CountryName" : "US" } { "_id" : ObjectId("5e57f69e2ae06a1609a00af3"), "Name" : "John", "CountryName" : "UK" } ... Read More
For this, use save() in MongoDB. Following is the syntax −var anyVaribaleName=yourValue db.anyCollectionName.save(yourVariableName); yourVariableName;Let us first create an object for our example −> var studentDetails={"StudentName":"Chris","ListOfMarks":[56,78,89],"ListOfSubject":["MySQL","Java","MongoDB"]};Let us save the above created object “studentDetails” −> db.demo40.save(studentDetails); WriteResult({ "nInserted" : 1 })Let us display the value −> studentDetails;This will produce the following output −{ "StudentName" : "Chris", "ListOfMarks" : [ 56, 78, 89 ], "ListOfSubject" : [ "MySQL", "Java", "MongoDB" ], "_id" : ObjectId("5e177757cfb11e5c34d898e2") }
For this, use $all in MongoDB. The $all operator in MongoDB selects the documents where the value of a field is an array that contains all the specified elements.Let us first create a collection with documents −> db.demo370.insertOne( ... { ... "Name" : "Chris", ... "details" : [ ... { ... "Subject" : "MySQL", ... "CountryName" : "US" ... }, ... { ... ... Read More
At first, switch to a particular database in MongoDB with the USE command as in the below syntax −use yourDatabaseName; db.getCollectionNames();Let us implement the above syntax to display collections of database WEB −> use web; switched to db web > db.getCollectionNames();This will produce the following output −[ "2015-myCollection", "2015-yourCollection", "2019-employeeCollection", "addColumnDemo", "applyConditionDemo", "calculateAverage", "calculateSumOfDocument", "changeSimpleFieldDemo", "check", "checkFieldDemo", "collationExample", "compoundIndexDemo", "countandsumdemo", "creatingAliasDemo", "decreasetimeusingindex", "demo1", "demo10", "demo11", "demo12", "demo13", "demo14", "demo15", "demo16", "demo17", "demo18", ... Read More
Yes, it is possible using the UPDATE() method. Let us create a collection with documents −> db.demo27.insertOne({"StudentDetails":{"101":{"Subject":["Java"]}}}); { "acknowledged" : true, "insertedId" : ObjectId("5e15f9e822d07d3b95082e7f") } > db.demo27.insertOne({"StudentDetails":{"101":{"Subject":["MySQL"]}}}); { "acknowledged" : true, "insertedId" : ObjectId("5e15f9eb22d07d3b95082e80") }Display all documents from a collection with the help of find() method −> db.demo27.find().pretty();This will produce the following output −{ "_id" : ObjectId("5e15f9e822d07d3b95082e7f"), "StudentDetails" : { "101" : { "Subject" : [ "Java" ] } } } { ... Read More
For this, use positional operator($). To increment a field value by 1, use $inc operator. Let us create a collection with documents −>db.demo39.insertOne({"ProductDetails":[{"ProductName":"Product-1", "ProductPrice":349}]}); { "acknowledged" : true, "insertedId" : ObjectId("5e176d54cfb11e5c34d898df") } >db.demo39.insertOne({"ProductDetails":[{"ProductName":"Product-2", "ProductPrice":998}]}); { "acknowledged" : true, "insertedId" : ObjectId("5e176d61cfb11e5c34d898e0") } >db.demo39.insertOne({"ProductDetails":[{"ProductName":"Product-3", "ProductPrice":145}]}); { "acknowledged" : true, "insertedId" : ObjectId("5e176d6acfb11e5c34d898e1") }Display all documents from a collection with the help of find() method −> db.demo39.find();This will produce the following output −{ "_id" : ObjectId("5e176d54cfb11e5c34d898df"), "ProductDetails" : [ { "ProductName" : "Product-1", "ProductPrice" : 349 } ] } { "_id" : ObjectId("5e176d61cfb11e5c34d898e0"), "ProductDetails" : [ ... Read More
To retrieve array values from a find query, use dot notation. Let us create a collection with documents −> db.demo38.insertOne({"ClientDetails":[{"ClientId":101, "ClientName":"Chris"}]}); { "acknowledged" : true, "insertedId" : ObjectId("5e176abccfb11e5c34d898d9") } > db.demo38.insertOne({"ClientDetails":[{"ClientId":102, "ClientName":"David"}]}); { "acknowledged" : true, "insertedId" : ObjectId("5e176ac7cfb11e5c34d898da") } > db.demo38.insertOne({"ClientDetails":[{"ClientId":103, "ClientName":"Mike"}]}); { "acknowledged" : true, "insertedId" : ObjectId("5e176ad0cfb11e5c34d898db") }Display all documents from a collection with the help of find() method −> db.demo38.find();This will produce the following output −{ "_id" : ObjectId("5e176abccfb11e5c34d898d9"), "ClientDetails" : [ { "ClientId" : 101, "ClientName" : "Chris" } ] } { "_id" : ObjectId("5e176ac7cfb11e5c34d898da"), "ClientDetails" : [ { ... Read More
REPL stands for Read-Evaluate-Print-Loop. It holds some states, and each statement in JShell has a state. This state denies the execution status of snippets and variables. It can be determined by the results of the eval() method of JShell instance, which evaluates the code.There are seven different status states listed below.DROPPED: The snippet is inactive.NONEXISTENT: The snippet is inactive because it does not yet exist.OVERWRITTEN: The snippet is inactive because it has been replaced by a new snippet.RECOVERABLE_DEFINED: The snippet is a declaration snippet with potentially recoverable unresolved references or other issues in its body.RECOVERABLE_NOT_DEFINED: The snippet is a declaration snippet with ... Read More