You can use aggregate framework to create an alias. Let us first create a collection with documents −> db.creatingAliasDemo.insertOne({_id:101, "Name":"John Doe"}); { "acknowledged" : true, "insertedId" : 101 } > db.creatingAliasDemo.insertOne({_id:102, "Name":"David Miller"}); { "acknowledged" : true, "insertedId" : 102 } > db.creatingAliasDemo.insertOne({_id:103, "Name":"Sam Williams"}); { "acknowledged" : true, "insertedId" : 103 }Following is the query to display all documents from the collection with the help of find() method −> db.creatingAliasDemo.find().pretty();This will produce the following output −{ "_id" : 101, "Name" : "John Doe" } { "_id" : 102, "Name" : "David Miller" } { "_id" : 103, "Name" : ... Read More

The findOne() returns first document if query matches otherwise returns null. The find() method does not return null, it returns a cursor.Let us implement the concept of find() and findOne() and create a collection with documents −> db.createCollection('emptyCollection'); { "ok" : 1 }Let us count how many documents are in the above collection −> db.emptyCollection.count();This will produce the following output −0There is no document present in the above collection.Following is the query to check the result with findOne() −> if(db.emptyCollection.findOne()){print("Returns Cursor")} else {print("Not returning cursor")} This will produce the following output −Not returning cursorFollowing is the query to check the ... Read More

The group is a type of method in MongoDB. It shouldn’t be created as a collection name. Even if you created it, you can easily remove it using getCollection('group').drop();). Let us first create a collection with documents −> db.createCollection('group'); { "ok" : 1 } > db.getCollection('group').insertOne({"StudentName":"Chris"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5cb80fe9623186894665ae3c") } > db.getCollection('group').insertOne({"StudentName":"Robert"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5cb80fef623186894665ae3d") }Following is the query to display all documents from the collection with the help of find() method −> db.getCollection('group').find().pretty();This will produce the following output −{ "_id" : ObjectId("5cb80fe9623186894665ae3c"), "StudentName" : "Chris" } { ... Read More

You can use $or operator for this. Let us first create a collection with documents −> db.applyConditionDemo.insertOne({"StudentName":"Larry", "StudentAge":21, "StudentMarks":45}); {    "acknowledged" : true,    "insertedId" : ObjectId("5cb80b78623186894665ae36") } > db.applyConditionDemo.insertOne({"StudentName":"Sam", "StudentAge":23, "StudentMarks":55}); {    "acknowledged" : true,    "insertedId" : ObjectId("5cb80b87623186894665ae37") } > db.applyConditionDemo.insertOne({"StudentName":"David", "StudentAge":21, "StudentMarks":65}); {    "acknowledged" : true,    "insertedId" : ObjectId("5cb80b95623186894665ae38") } > db.applyConditionDemo.insertOne({"StudentName":"Carol", "StudentAge":24, "StudentMarks":78}); {    "acknowledged" : true,    "insertedId" : ObjectId("5cb80ba3623186894665ae39") } > db.applyConditionDemo.insertOne({"StudentName":"Chris", "StudentAge":21, "StudentMarks":88}); {    "acknowledged" : true,    "insertedId" : ObjectId("5cb80bae623186894665ae3a") } > db.applyConditionDemo.insertOne({"StudentName":"Robert", "StudentMarks":98}); {    "acknowledged" : true,    "insertedId" : ObjectId("5cb80c3d623186894665ae3b") }Following is the ... Read More

You can use $pull operator for this. Let us first create a collection with documents −> db.removeNullDemo.insertOne( ... { ...    "_id" : 1, ...    "StudentDetails" : [ ...       { ...          "FirstName": "John", ...          "LastName":"Smith", ... ...       }, ...       { ...          "Age":21 ...       }, ...       null ... ...    ] ... } ... ); { "acknowledged" : true, "insertedId" : 1 } > db.removeNullDemo.insertOne( ... { ...    "_id" : 2, ... ... Read More

This SHOW DBS command won’t show the databases because you may have not created a document for a collection. If you will create document for a collection then the created database will be visible.Let us implement the above concept and create a database −> use web; switched to db webFollowing is the query to show all databases −> show dbs;This will produce the following output −admin 0.001GB config 0.000GB local 0.000GB my 0.001GB sample 0.001GB sampleDemo 0.000GB studentSearch 0.000GB test 0.010GB university 0.000GBAbove, the WEB database is not visible since we haven’t created a collection in the same database.In order ... Read More

Too return a specific field, use the find() method in MongoDB. Let us first create a collection with documents −> db.specificFieldDemo.insertOne({"FirstName":"John", "LastName":"Doe"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5cb8019a623186894665ae31") } > db.specificFieldDemo.insertOne({"FirstName":"John", "LastName":"Smith"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5cb801ab623186894665ae32") } > db.specificFieldDemo.insertOne({"FirstName":"David", "LastName":"Miller"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5cb801b3623186894665ae33") } > db.specificFieldDemo.insertOne({"FirstName":"Sam", "LastName":"Williams"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5cb801bf623186894665ae34") }Following is the query to display all documents from the collection with the help of find() method −> db.specificFieldDemo.find().pretty();This will produce the following output −{    "_id" : ObjectId("5cb8019a623186894665ae31"),   ... Read More

In order to remove the numeric collection name, use the following syntaxdb.getCollection("yourNumericCollectionName").drop();First, create a numeric collection. Following is the query> db.createCollection("2536464"); { "ok" : 1 }Now insert some documents in the above collection. Following is the query> db.getCollection("2536464").insertOne({"Record":1}); {    "acknowledged" : true,    "insertedId" : ObjectId("5ca254a46304881c5ce84b8e") } > db.getCollection("2536464").insertOne({"Record":2}); {    "acknowledged" : true,    "insertedId" : ObjectId("5ca254a76304881c5ce84b8f") } > db.getCollection("2536464").insertOne({"Record":3}); {    "acknowledged" : true,    "insertedId" : ObjectId("5ca254a96304881c5ce84b90") }Following is the query to display all documents from a collection with the help of find() method> db.getCollection("2536464").find().pretty();This will produce the following output{ "_id" : ObjectId("5ca254a46304881c5ce84b8e"), "Record" : 1 ... Read More

To get number of updated documents in MongoDB, you need to use runCommand along with getlasterror.Let us first create a collection with documents> db.getNumberOfUpdatedDocumentsDemo.insertOne({"StudentName":"David"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5ca28c1d6304881c5ce84bad") } > db.getNumberOfUpdatedDocumentsDemo.insertOne({"StudentName":"Chris"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5ca28c226304881c5ce84bae") } > db.getNumberOfUpdatedDocumentsDemo.insertOne({"StudentName":"Robert"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5ca28c276304881c5ce84baf") } > db.getNumberOfUpdatedDocumentsDemo.insertOne({"StudentName":"Ramit"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5ca28c366304881c5ce84bb0") } > db.getNumberOfUpdatedDocumentsDemo.insertOne({"StudentName":"Adam"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5ca28c436304881c5ce84bb1") }Following is the query to display all documents from a collection with the help of find() method:> db.getNumberOfUpdatedDocumentsDemo.find().pretty();This will ... Read More

To find the highest value from sub-arrays in documents, you can use an aggregate framework. Let us first create a collection with documents> db.findHighestValueDemo.insertOne(    ... {       ... _id: 10001,       ... "StudentDetails": [          ... { "StudentName": "Chris", "StudentMathScore": 56},          ... { "StudentName": "Robert", "StudentMathScore":47 },          ... { "StudentName": "John", "StudentMathScore": 98 }]    ... } ... ); { "acknowledged" : true, "insertedId" : 10001 } > db.findHighestValueDemo.insertOne(    ... {       ... _id: 10002,       ... "StudentDetails": [ ... Read More