The findOne() in MongoDB returns only a single document. Let us create a collection with documents −> db.demo230.insertOne({"FirstName":"Chris"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e3fc4d2f4cebbeaebec513e") } > db.demo230.insertOne({"FirstName":"Bob"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e3fc4d5f4cebbeaebec513f") } > db.demo230.insertOne({"FirstName":"Chris"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e3fc4dbf4cebbeaebec5140") } > db.demo230.insertOne({"FirstName":"David"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e3fc4dff4cebbeaebec5141") } > db.demo230.insertOne({"FirstName":"David"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e3fc4e1f4cebbeaebec5142") }Display all documents from a collection with the help of find() method −> db.demo230.find();This will produce the following output −{ "_id" : ObjectId("5e3fc4d2f4cebbeaebec513e"), "FirstName" : ... Read More

For sparse index, use sparse:true. Following is the query to create an index −> db.demo229.ensureIndex({"ClientName":1}, {unique: true}); {    "createdCollectionAutomatically" : true,    "numIndexesBefore" : 1,    "numIndexesAfter" : 2,    "ok" : 1 }Following is the query to display indexes −> db.demo229.getIndexes();This will produce the following output −[    {       "v" : 2,       "key" : {          "_id" : 1       },       "name" : "_id_",       "ns" : "test.demo229"    },    {       "v" : 2,       "unique" ... Read More

For this, set regex in MongoDB find(). Let us create a collection with documents −> db.demo228.insertOne({"Subjects":["MongoDB", "Java"]}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e3fa51f03d395bdc213473b") } > db.demo228.insertOne({"Subjects":["MongoDB", "Java", "MySQL"]}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e3fa52c03d395bdc213473c") }Display all documents from a collection with the help of find() method −> db.demo228.find();This will produce the following output −{ "_id" : ObjectId("5e3fa51f03d395bdc213473b"), "Subjects" : [ "MongoDB", "Java" ] } { "_id" : ObjectId("5e3fa52c03d395bdc213473c"), "Subjects" : [ "MongoDB", "Java", "MySQL" ] }Following is the query to find documents where at least one item from an array is not in the ... Read More

Let us create a collection with documents −> db.demo227.insertOne({"_id":"101", "Name":"Chris"}); { "acknowledged" : true, "insertedId" : "101" } > db.demo227.insertOne({"_id":"102", "Name":"Bob"}); { "acknowledged" : true, "insertedId" : "102" }Display all documents from a collection with the help of find() method −> db.demo227.find();This will produce the following output −{ "_id" : "101", "Name" : "Chris" } { "_id" : "102", "Name" : "Bob" }Following is the query to update a set of documents from a list of key value pairs −> var bulkUpdateValue = [{"_id": "101", "Name": "Robert"}, ...   {"_id": "102", "Name": "Sam"} ...]; > var bulkUpdate = db.demo227.initializeUnorderedBulkOp(); > ... Read More

For this, use the $project. The $project takes a document that can specify the inclusion of fields, the suppression of the _id field, the addition of new fields, and the resetting of the values of existing fieldsLet us first create a collection with documents −> db.demo226.insertOne({"Name":"Chris", "Age":21}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e3f9be803d395bdc2134738") } > db.demo226.insertOne({"Name":"Bob", "Age":20}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e3f9bf003d395bdc2134739") } > db.demo226.insertOne({"Name":"David", "Age":22}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e3f9bf803d395bdc213473a") }Display all documents from a collection with the help of find() method −> db.demo226.find();This will produce the following ... Read More

To get the last two values, use MongoDB $slice. Let us create a collection with documents −> db.demo173.insertOne({"ListOfValues":[10,40,100,560,700,900]}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e383a4f9e4f06af551997e4") }Display all documents from a collection with the help of find() method −> db.demo173.find().pretty();This will produce the following output −{    "_id" : ObjectId("5e383a4f9e4f06af551997e4"),    "ListOfValues" : [ 10, 40, 100, 560, 700, 900 ] }Following is the query to get the last two values −> db.demo173.find({}, { "ListOfValues": { "$slice": -2 } } );This will produce the following output −{ "_id" : ObjectId("5e383a4f9e4f06af551997e4"), "ListOfValues" : [ 700, 900 ] }

To remove item from array, use $pull in MongoDB. Let us create a collection with documents −> db.demo224.insertOne({"ListOfTechnology":["Spring", "Hibernate", "Java"]}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e3ee6d103d395bdc2134733") } > db.demo224.insertOne({"ListOfTechnology":["Groovy"]}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e3ee6ec03d395bdc2134734") }Display all documents from a collection with the help of find() method −> db.demo224.find();This will produce the following output −{ "_id" : ObjectId("5e3ee6d103d395bdc2134733"), "ListOfTechnology" : [ "Spring", "Hibernate", "Java" ] } { "_id" : ObjectId("5e3ee6ec03d395bdc2134734"), "ListOfTechnology" : [ "Groovy" ] }Following is the query to remove item from array in MongoDB −>db.demo224.update({_id:ObjectId("5e3ee6d103d395bdc2134733")}, {$pull:{"ListOfTechnology":"Java"}}); WriteResult({ "nMatched" : 1, "nUpserted" : ... Read More

To compare multiple properties, use $where in MongoDB. Let us create a collection with documents −> db.demo223.insertOne({"Scores":[56, 78]}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e3ee4ca03d395bdc2134730") } > db.demo223.insertOne({"Scores":[88, 45]}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e3ee4d103d395bdc2134731") } > db.demo223.insertOne({"Scores":[98, 79]}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e3ee4d803d395bdc2134732") }Display all documents from a collection with the help of find() method −> db.demo223.find();This will produce the following output −{ "_id" : ObjectId("5e3ee4ca03d395bdc2134730"), "Scores" : [ 56, 78 ] } { "_id" : ObjectId("5e3ee4d103d395bdc2134731"), "Scores" : [ 88, 45 ] } { "_id" : ObjectId("5e3ee4d803d395bdc2134732"), "Scores" : ... Read More

To add new array element in a MongoDB document, use $(projection) along with update(). Let us create a collection with documents −>db.demo222.insertOne({"details":[{"StudentName":"Chris", "StudentMarks":78}, {"StudentName":"David", "StudentMarks":89}]}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e3ee31703d395bdc213472f") }Display all documents from a collection with the help of find() method −> db.demo222.find().pretty();This will produce the following output −{    "_id" : ObjectId("5e3ee31703d395bdc213472f"),    "details" : [       {          "StudentName" : "Chris",          "StudentMarks" : 78       },       {          "StudentName" : "David",          "StudentMarks" ... Read More

For searching a specific word, use /searchWord/ with regex. Let us create a collection with documents −> db.demo221.insertOne({"Details":{"StudentName":"Chris", "StudentAge":21}}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e3ee15d03d395bdc213472b") } > db.demo221.insertOne({"Details":{"StudentName":"John", "StudentAge":20}}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e3ee16503d395bdc213472c") } > db.demo221.insertOne({"Details":{"StudentName":"Bob", "StudentAge":22}}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e3ee16b03d395bdc213472d") } > db.demo221.insertOne({"Details":{"StudentName":"john", "StudentAge":24}}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e3ee17303d395bdc213472e") }Display all documents from a collection with the help of find() method −> db.demo221.find();This will produce the following output −{ "_id" : ObjectId("5e3ee15d03d395bdc213472b"), "Details" : { "StudentName" : "Chris", "StudentAge" : 21 } ... Read More