To check for existing documents/embedded documents, use $exists in MongoDB. Let us create a collection with documents −> db.demo322.insertOne( ...  {'id':1001, ...    'details':[{'Score':10000, Name:"Bob"}, ...       {'Score':98000, Name:"Sam"} ...    ] ... } ... ); {    "acknowledged" : true,    "insertedId" : ObjectId("5e5113e2f8647eb59e56206c") } > db.demo322.insertOne( ... {'id':10002, ...    'details':[{'Score':9000}, ...       {'Score':91000} ...       ] ... } ... ); {    "acknowledged" : true,    "insertedId" : ObjectId("5e5113faf8647eb59e56206d") }Display all documents from a collection with the help of find() method −> db.demo322.find();This will produce the following output −{    "_id" ... Read More

Let us first create a collection with documents wherein we are storing array values −>db.demo321.insertOne({"UserDetails":[{"UserId":101, "UserName":"Chris"}, {"UserId":102, "UserName":"Mike"}]}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e511248f8647eb59e56206a") } >db.demo321.insertOne({"UserDetails":[{"UserId":103, "UserName":"Bob"}, {"UserId":104, "UserName":"Sam"}]}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e511259f8647eb59e56206b") }Display all documents from a collection with the help of find() method −> db.demo321.find();This will produce the following output −{ "_id" : ObjectId("5e511248f8647eb59e56206a"), "UserDetails" : [ { "UserId" : 101, "UserName" : "Chris" }, { "UserId" : 102, "UserName" : "Mike" } ] } { "_id" : ObjectId("5e511259f8647eb59e56206b"), "UserDetails" : [ { "UserId" : 103, "UserName" : "Bob" }, ... Read More

The fastest way of updating is update(). Let us create a collection with documents and see how update() works −> db.demo320.insertOne({"Name":"Chris"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e50ee51f8647eb59e562066") } > db.demo320.insertOne({"Name":"Robert"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e50ee55f8647eb59e562067") } > db.demo320.insertOne({"Name":"Mike"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e50ee59f8647eb59e562068") } > db.demo320.insertOne({"Name":"Sam"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e50ee5bf8647eb59e562069") }Display all documents from a collection with the help of find() method −> db.demo320.find();This will produce the following output −{ "_id" : ObjectId("5e50ee51f8647eb59e562066"), "Name" : "Chris" } { "_id" : ObjectId("5e50ee55f8647eb59e562067"), "Name" : "Robert" ... Read More

In MongoDB, you cannot use capped for sub-collection. However, use capped on the overall document. To display a specific number of values from an array, prefer $slice.Let us create a collection with documents −> db.demo319.insertOne({"Scores":[100, 345, 980, 890]}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e50ecf6f8647eb59e562064") } > db.demo319.insertOne({"Scores":[903, 10004, 84575, 844]}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e50ed01f8647eb59e562065") }Display all documents from a collection with the help of find() method −> db.demo319.find().pretty();This will produce the following output −{    "_id" : ObjectId("5e50ecf6f8647eb59e562064"),    "Scores" : [       100,       345,     ... Read More

To pull a specific value, use UPDATE with $pull. Let us create a collection with documents −> db.demo318.insertOne({Subject:["MySQL", "MongoDB", "Java"]}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e50ea6df8647eb59e562062") } > db.demo318.insertOne({Subject:["Spring", "Hibernate"]}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e50ea78f8647eb59e562063") }Display all documents from a collection with the help of find() method −> db.demo318.find();This will produce the following output −{ "_id" : ObjectId("5e50ea6df8647eb59e562062"), "Subject" : [ "MySQL", "MongoDB", "Java" ] } { "_id" : ObjectId("5e50ea78f8647eb59e562063"), "Subject" : [ "Spring", "Hibernate" ] }Following is the query to $pull a specific value “Hibernate” −> db.demo318.update({Subject:"Hibernate"}, {$pull:{"Subject":"Hibernate"}}); WriteResult({ "nMatched" : 1, ... Read More

To get values greater than a specific value, use $gt along with find(). Let us create a collection with documents −> db.demo317.insertOne( ...    {'id':101, ...       'details':[{'Score':78, Name:"Chris"}, ...          {'Score':88, Name:"David"} ...       ] ...    } ... ); {    "acknowledged" : true,    "insertedId" : ObjectId("5e50e69cf8647eb59e562060") } > db.demo317.insertOne( ...    {'id':102, ...    'details':[{'Score':90, Name:"Chris"}, ...       {'Score':91, Name:"David"} ...       ] ...    } ... ); {    "acknowledged" : true,    "insertedId" : ObjectId("5e50e6adf8647eb59e562061") }Display all documents from a collection with the ... Read More

For this, use ensureIndex() and set unique:true. Let us create a collection with documents. Here, when we try to inert duplicate item, then a duplicate key error occurs −> db.demo316.ensureIndex({"SubjectName":1}, {unique:true}); {    "createdCollectionAutomatically" : true,    "numIndexesBefore" : 1,    "numIndexesAfter" : 2,    "ok" : 1 } > db.demo316.insertOne({"SubjectName":"MySQL"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e50e378f8647eb59e56205d") } > db.demo316.insertOne({"SubjectName":"MongoDB"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e50e37df8647eb59e56205e") } > db.demo316.insertOne({"SubjectName":"MongoDB"}); 2020-02-22T13:47:05.186+0530 E QUERY [js] WriteError: E11000 duplicate key error collection: test.demo316 index: SubjectName_1 dup key: { : "MongoDB" } : WriteError({    "index" : 0, ... Read More

To update the nested document, use $set. Let us create a collection with documents −> db.demo315.insertOne({ _id :101, ...  details: [ ...     {Name: 'Chris', subjects: [{id:1001, SubjectName:"MySQL"}]} ...  ] ... } ...) { "acknowledged" : true, "insertedId" : 101 }Display all documents from a collection with the help of find() method −> db.demo315.find().pretty();This will produce the following output −{    "_id" : 101,    "details" : [       {          "Name" : "Chris",          "subjects" : [             {             ... Read More

You can use positional $ operator. Let us first create a collection with documents −> db.demo22.insertOne( ...    { ...       ProductId:101, ... ...       ProductDetails: ...       [ ...          { ...             ProductFirstPrice: '35', ...             ProductSecondPrice: '75' ...          }, ...          { ...             ProductFirstPrice: '', ...             ProductSecondPrice:'' ...          }, ...          { ... Read More

To update child objects, use $set in MongoDB. Let us first create a collection with documents −>db.demo21.insertOne({"StudentId":"STU-101", "StudentDetails":{"StudentName":"Chris", "StudentAge":21}}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e14be8922d07d3b95082e6f") }Display all documents from a collection with the help of find() method −> db.demo21.find().pretty();This will produce the following output −{    "_id" : ObjectId("5e14be8922d07d3b95082e6f"),    "StudentId" : "STU-101",    "StudentDetails" : {       "StudentName" : "Chris",       "StudentAge" : 21    } }Following is the query to update child objects in MongoDB −> db.demo21.update({"StudentId":'STU-101'}, {$set:{'StudentDetails.StudentName':'Robert'}}); WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })Display all documents ... Read More