For this, use $group in MongoDB aggregation. Let us create a collection with documents −> db.demo639.insertOne( ...    { ...       "_id" : 1, ...       "CountryName" : "US", ...       "Info1" : { ...          "Name" : "Chris", ...          "SubjectName" : "MySQL", ...          "Marks" : 78 ...       }, ...       "Info2" : { ...          "Name" : "Chris", ...          "SubjectName" : "MySQL", ...          "Marks" : 78 ... Read More

To filter items by fields and subfields, use dot notation. Let us create a collection with documents −> db.demo638.insert({Name:"Chris"}); WriteResult({ "nInserted" : 1 }) > db.demo638.insert({Name:"David", details:{Subject:"MongoDB"}}); WriteResult({ "nInserted" : 1 })Display all documents from a collection with the help of find() method −> db.demo638.find().pretty();This will produce the following output −{ "_id" : ObjectId("5e9c28666c954c74be91e6de"), "Name" : "Chris" }    {       "_id" : ObjectId("5e9c28866c954c74be91e6df"),       "Name" : "David",       "details" : {          "Subject" : "MongoDB"    } }Following is the query to filter items by multiple fields and subfields −> ... Read More

For information on the query plan, use explain() in MongoDB. Let us create a collection with documents −> db.demo637.ensureIndex({ClientName:1}); {    "createdCollectionAutomatically" : true,    "numIndexesBefore" : 1,    "numIndexesAfter" : 2,    "ok" : 1 } > db.demo637.insert({ClientName:"John"}); WriteResult({ "nInserted" : 1 }) > db.demo637.insert({ClientName:"Bob"}); WriteResult({ "nInserted" : 1 }) > db.demo637.insert({ClientName:"Johnson"}); WriteResult({ "nInserted" : 1 })Display all documents from a collection with the help of find() method −> db.demo637.find();This will produce the following output −{ "_id" : ObjectId("5e9c26916c954c74be91e6db"), "ClientName" : "John" } { "_id" : ObjectId("5e9c26936c954c74be91e6dc"), "ClientName" : "Bob" } { "_id" : ObjectId("5e9c269d6c954c74be91e6dd"), "ClientName" : "Johnson" }Case ... Read More

Let us create a collection with documents −> db.demo636.insert({id:1}); WriteResult({ "nInserted" : 1 }) > db.demo636.insert({id:2}); WriteResult({ "nInserted" : 1 }) > db.demo636.insert({id:3}); WriteResult({ "nInserted" : 1 }) > db.demo636.insert({id:4}); WriteResult({ "nInserted" : 1 }) > db.demo636.insert({id:5}); WriteResult({ "nInserted" : 1 }) > db.demo636.insert({id:6}); WriteResult({ "nInserted" : 1 })Display all documents from a collection with the help of find() method −> db.demo636.find();This will produce the following output −{ "_id" : ObjectId("5e9c127b6c954c74be91e6d2"), "id" : 1 } { "_id" : ObjectId("5e9c127e6c954c74be91e6d3"), "id" : 2 } { "_id" : ObjectId("5e9c127f6c954c74be91e6d4"), "id" : 3 } { "_id" : ObjectId("5e9c12816c954c74be91e6d5"), "id" : 4 } { ... Read More

To calculate frequency, group with $group in aggregate(). Let us create a collection with documents −> db.demo635.insertOne({Name:"Chris"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e9c10f06c954c74be91e6cc") } > db.demo635.insertOne({Name:"David"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e9c10f46c954c74be91e6cd") } > db.demo635.insertOne({Name:"David"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e9c10f66c954c74be91e6ce") } > db.demo635.insertOne({Name:"Chris"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e9c10f86c954c74be91e6cf") } > db.demo635.insertOne({Name:"Bob"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e9c10fb6c954c74be91e6d0") } > db.demo635.insertOne({Name:"Chris"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e9c10fc6c954c74be91e6d1") }Display all documents from a collection with the help of find() method −> db.demo635.find();This ... Read More

Use forEach() and traverse to find student name David update new marks for the same student. Let us create a collection with documents −> db.demo634.insertOne({Name:"Chris", "Marks":76}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e9c0ea66c954c74be91e6c9") } > db.demo634.insertOne({Name:"Bob", "Marks":67}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e9c0ead6c954c74be91e6ca") } > db.demo634.insertOne({Name:"David", "Marks":37}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e9c0eb76c954c74be91e6cb") }Display all documents from a collection with the help of find() method −> db.demo634.find();This will produce the following output −{ "_id" : ObjectId("5e9c0ea66c954c74be91e6c9"), "Name" : "Chris", "Marks" : 76 } { "_id" : ObjectId("5e9c0ead6c954c74be91e6ca"), "Name" : "Bob", "Marks" : ... Read More

To skip values in MongoDB, use skip() along with limit(). For 5 values, use limit(5). Let us create a collection with documents −> db.demo633.insertOne({"Value":10}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e9c0be76c954c74be91e6c1") } > db.demo633.insertOne({"Value":20}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e9c0bea6c954c74be91e6c2") } > db.demo633.insertOne({"Value":30}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e9c0bec6c954c74be91e6c3") } > db.demo633.insertOne({"Value":40}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e9c0bef6c954c74be91e6c4") } > db.demo633.insertOne({"Value":50}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e9c0bf16c954c74be91e6c5") } > db.demo633.insertOne({"Value":60}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e9c0bf36c954c74be91e6c6") } > db.demo633.insertOne({"Value":70}); {    "acknowledged" : ... Read More

To remove values from a matrix, use $pull in MongoDB. Let us create a collection with documents −> db.demo632.insertOne( ...    { ...       "arrayMatrix": [ ...          [10, 20], ...          [10, 20], ...          [10, 20], ...          [10, 20], ...          [10, 20], ...          [10, 20] ...       ] ...    } ... ); {    "acknowledged" : true,    "insertedId" : ObjectId("5e9b27b46c954c74be91e6c0") }Display all documents from a collection with the help of find() ... Read More

Use $unwind twice for specific embedded document in MongoDB. Let us create a collection with documents −> db.demo631.insert( ...    { ...       id: "101", ...       Info1: [ ...          { ...             CountryName : "US", ...             Info2 : [ ...                { ...                   Name:"Chris", ...                   Age:24 ...                }, { ... Read More

To sort documents, use sort() along with find(). Let us create a collection with documents −> db.demo630.insertOne({"Value":10}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e9b080e6c954c74be91e6ba") } > db.demo630.insertOne({"Value":200}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e9b08116c954c74be91e6bb") } > db.demo630.insertOne({"Value":40}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e9b08146c954c74be91e6bc") } > db.demo630.insertOne({"Value":60}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e9b08176c954c74be91e6bd") }Display all documents from a collection with the help of find() method −> db.demo630.find();This will produce the following output −{ "_id" : ObjectId("5e9b080e6c954c74be91e6ba"), "Value" : 10 } { "_id" : ObjectId("5e9b08116c954c74be91e6bb"), "Value" : 200 } { "_id" : ... Read More