Let us first create a collection with documents −> db.demo121.insertOne( ...    { ...       "Id" : 101, ...       "Details" : [ ...          { ...             "SubjectId" : "1", ...             "SubjectName" : "MongoDB", ...             "Score" : 76 ...          }, ...          { ...             "SubjectId" : "2", ...             "SubjectName" : "MySQL", ...         ... Read More

For this, use aggregate() in MongoDB. Let us create a collection with documents −> db.demo120.insertOne( ...    { ...       'Name': 'Chris', ...       'Subjects': [ 'MySQL', 'MongoDB', 'Java', 'Python' ] ...    } ... ); {    "acknowledged" : true,    "insertedId" : ObjectId("5e2f11aed8f64a552dae6365") } > db.demo120.insertOne( ...    { ...       'Name': 'Bob', ...       'Subjects': [ 'C', 'MongoDB' ] ...    } ... ); {    "acknowledged" : true,    "insertedId" : ObjectId("5e2f11afd8f64a552dae6366") }Display all documents from a collection with the help of find() method −> db.demo120.find();This will produce ... Read More

To prevent duplicates of multiple fields, use ensureIndex() and set unique:true. Let us create a collection with documents −> db.demo272.ensureIndex({"FirstName":1, "Subject":1}, {unique:true}); {    "createdCollectionAutomatically" : true,    "numIndexesBefore" : 1,    "numIndexesAfter" : 2,    "ok" : 1 } > db.demo272.insertOne({"FirstName":"Chris", "Subject":"MySQL"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e48232a1627c0c63e7dbabf") } > db.demo272.insertOne({"FirstName":"Chris", "Subject":"MongoDB"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e48232f1627c0c63e7dbac0") } > db.demo272.insertOne({"FirstName":"David", "Subject":"MySQL"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e48233a1627c0c63e7dbac1") } > db.demo272.insertOne({"FirstName":"Chris", "Subject":"MySQL"}); 2020-02-15T22:28:55.137+0530 E QUERY    [js] WriteError: E11000 duplicate key error collection: test.demo272 index: FirstName_1_Subject_1 dup key: { : ... Read More

Set a custom variable and use update() along with $inc to increment. Let us create a collection with documents −> db.demo271.insertOne({"Marks":56}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e4821211627c0c63e7dbabc") } > db.demo271.insertOne({"Marks":78}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e4821241627c0c63e7dbabd") } > db.demo271.insertOne({"Marks":72}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e48212b1627c0c63e7dbabe") }Display all documents from a collection with the help of find() method −> db.demo271.find();This will produce the following output −{ "_id" : ObjectId("5e4821211627c0c63e7dbabc"), "Marks" : 56 } { "_id" : ObjectId("5e4821241627c0c63e7dbabd"), "Marks" : 78 } { "_id" : ObjectId("5e48212b1627c0c63e7dbabe"), "Marks" : 72 }Following is the query ... Read More

Let us first create a collection with documents −> db.demo270.insertOne({"ClientName":"Chirs", "Age":34}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e481e371627c0c63e7dbab8") } > db.demo270.insertOne({"ClientName":"David", "Age":31}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e481e3d1627c0c63e7dbab9") } > db.demo270.insertOne({"ClientName":"Bob", "Age":31}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e481e431627c0c63e7dbaba") } > db.demo270.insertOne({"ClientName":"Carol", "Age":36}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e481e491627c0c63e7dbabb") }Display all documents from a collection with the help of find() method −> db.demo270.find();This will produce the following output −{ "_id" : ObjectId("5e481e371627c0c63e7dbab8"), "ClientName" : "Chirs", "Age" : 34 } { "_id" : ObjectId("5e481e3d1627c0c63e7dbab9"), "ClientName" : "David", "Age" : 31 } ... Read More

For this, simply use find(). Set the fields you don’t want to select to 0. Let us create a collection with documents −> db.demo269.insertOne({StudentId:101, StudentSubject:"MySQL"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e481caa1627c0c63e7dbab4") } > db.demo269.insertOne({StudentId:102, StudentSubject:"Java"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e481cb11627c0c63e7dbab5") } > db.demo269.insertOne({StudentId:103, StudentSubject:"MongoDB"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e481cb21627c0c63e7dbab6") } > db.demo269.insertOne({StudentId:104, StudentSubject:"C"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e481cb21627c0c63e7dbab7") }Display all documents from a collection with the help of find() method −> db.demo269.find();This will produce the following output −{ "_id" : ObjectId("5e481caa1627c0c63e7dbab4"), "StudentId" : 101, "StudentSubject" ... Read More

To search a value, simply use $where in MongoDB. Let us create a collection with documents −> db.demo268.insertOne( ...   { ...      "details" : { ...         "101" : "John", ...         "1001" : "Bob" ...      } ...   } ...); {    "acknowledged" : true,    "insertedId" : ObjectId("5e4816141627c0c63e7dbaaf") }Display all documents from a collection with the help of find() method −> db.demo268.find();This will produce the following output −{ "_id" : ObjectId("5e4816141627c0c63e7dbaaf"), "details" : { "101" : "John", "1001" : "Bob" } }Following is the query to search a ... Read More

For descending order, use -1, which specifies sorting order for sort(), Let us create a collection with documents −> db.demo267.insertOne({id:100, "Name":"Chris"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e4811951627c0c63e7dbaab") } > db.demo267.insertOne({id:100, "Name":"Adam"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e48119e1627c0c63e7dbaac") } > db.demo267.insertOne({id:100, "Name":"David"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e4811a51627c0c63e7dbaad") } > db.demo267.insertOne({id:100, "Name":"Bob"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e4811ab1627c0c63e7dbaae") }Display all documents from a collection with the help of find() method −> db.demo267.find().pretty(); {    "_id" : ObjectId("5e4811951627c0c63e7dbaab"),    "id" : 100,    "Name" : "Chris" } {    "_id" ... Read More

The $not operator won’t invert a complex expression. Therefore, use $and or $or with $ne operator.Let us create a collection with documents −> db.demo266.insertOne({"active1":true, "active2":false}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e480f4b1627c0c63e7dbaa7") } > db.demo266.insertOne({"active1":true, "active2":true}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e480f501627c0c63e7dbaa8") } > db.demo266.insertOne({"active1":false, "active2":false}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e480f561627c0c63e7dbaa9") } > db.demo266.insertOne({"active1":false, "active2":true}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e480f701627c0c63e7dbaaa") }Display all documents from a collection with the help of find() method −> db.demo266.find();This will produce the following output −{ "_id" : ObjectId("5e480f4b1627c0c63e7dbaa7"), "active1" : true, "active2" ... Read More

To update only certain fields, use $set. Let us create a collection with documents −> db.demo265.insertOne({"id":101, "Name":"Chris"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e480d781627c0c63e7dbaa4") } > db.demo265.insertOne({"id":102, "Name":"Bob"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e480d7d1627c0c63e7dbaa5") } > db.demo265.insertOne({"id":103, "Name":"David"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e480d841627c0c63e7dbaa6") }Display all documents from a collection with the help of find() method −> db.demo265.find();This will produce the following output −{ "_id" : ObjectId("5e480d781627c0c63e7dbaa4"), "id" : 101, "Name" : "Chris" } { "_id" : ObjectId("5e480d7d1627c0c63e7dbaa5"), "id" : 102, "Name" : "Bob" } { "_id" : ObjectId("5e480d841627c0c63e7dbaa6"), "id" : 103, ... Read More