To filter out sub documents, use MongoDB aggregate and in that, use $unwind. Let us create a collection with documents −> db.demo662.insertOne( ... { ...    "details":[ ...   { ...       Name:"Chris", ...       Marks:35 ...    }, ...    { ...       ... Read More

For faster search, create index. For this, use createIndex(). Let us create a collection with documents −> db.demo661.createIndex({ListOfName:1}); {    "createdCollectionAutomatically" : true,    "numIndexesBefore" : 1,    "numIndexesAfter" : 2,    "ok" : 1 } > db.demo661.insertOne({_id:1, ListOfName:["John", "Robert", "David"]}); { "acknowledged" : true, "insertedId" : 1 } > ... Read More

You can use $group. Let us create a collection with documents −> db.demo659.insertOne({Name:"Chris", CountryName:"US", "Marks":50}); {    "acknowledged" : true,    "insertedId" : ObjectId("5ea1a50724113ea5458c7cf9") } > db.demo659.insertOne({Name:"David", CountryName:"US", "Marks":60}); {    "acknowledged" : true,    "insertedId" : ObjectId("5ea1a50724113ea5458c7cfa") } > db.demo659.insertOne({Name:"Mike", CountryName:"US", "Marks":55}); {    "acknowledged" : true,    "insertedId" ... Read More

For unique index, set unique − true while creating an index. Let us create a collection with documents −> db.demo658.createIndex({FirstName:1}, {unique:true, sparse:true}); {    "createdCollectionAutomatically" : true,    "numIndexesBefore" : 1,    "numIndexesAfter" : 2,    "ok" : 1 } > > db.demo658.insertOne({"FirstName":"John", "LastName":"Smith"}); {    "acknowledged" : true,   ... Read More

To group by dates, use $group in MongoDB aggregate. Let us create a collection with documents −> db.demo657.insertOne({ ...       id: 1, ...       Name: "Chris", ...       DueDate: new ISODate("2020-04-22") ...    } ... ); {    "acknowledged" : true,    "insertedId" : ... Read More

To push and slice in MongoDB, use $push and $slice. Let us create a collection with documents −> db.demo656.insertOne({Name:"John"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5ea060264deddd72997713cf") }Display all documents from a collection with the help of find() method −> db.demo656.find();This will produce the following output −{ "_id" : ... Read More

To clear, use dropDatabase. Following is the syntax −use yourDatabaseName; db.dropDatabase();To clear a MongoDB database, first show all the databases −> show dbsThis will produce the following output −MyDB    0.000GB admin    0.000GB config    0.000GB local    0.000GB onlinecustomertracker 0.000GB test    0.006GBNow, let us delete the database ... Read More

The findOne() returns one document that satisfies the specified query criteria on the collection. Let us create a collection with documents −> db.demo655.insertOne({subject:"MySQL"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5ea050254deddd72997713cc") } > db.demo655.insertOne({subject:"MongoDB"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5ea0502b4deddd72997713cd") } > db.demo655.insertOne({subject:"Java"}); {    "acknowledged" ... Read More

Yes, using $in is faster. Let us see an example and create a collection with documents −> db.demo653.insertOne({subject:"MySQL"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5ea04b274deddd72997713c0") } > db.demo653.insertOne({subject:"MongoDB"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5ea04b304deddd72997713c1") } > db.demo653.insertOne({subject:"Java"}); {    "acknowledged" : true,    "insertedId" : ... Read More

Use $sort in MongoDB aggregation. Let us create a collection with documents −> db.demo652.insertOne({ ...    value:10, ...    "details" : [{ ...       "ProductName" : "Product-1", ...       "ProductQuantity" : 8, ...       "ProductPrice" : 500 ...    }, { ...     ... Read More