Use the $slice operator. Let us first create a collection with documents −> db.limitAndSliceProjectionDemo.insertOne(    {       "_id" : 101,       "UserName" : "Carol",       "UserAge" : 26,       "UserMesssage" : [          "Hi",          "Hello",          "Bye",          "Awesome",          "Good",          "Bad",          "Nice",          "Good Night",          "Good Morning"       ]    } ); { "acknowledged" : true, "insertedId" : ... Read More

Use the $push operator to add a sub-document. Let us first create a collection with documents −> db.subDocumentToSubDocumentDemo.insertOne(    {       "_id" :101,       "StudentName" : "Larry",       "StudentAge" : 21,       "StudentDetails" : [          {             "StudentCountryName" : "US",             "StudentFavouriteSubjectList" : [ ]          }       ]    } ); { "acknowledged" : true, "insertedId" : 101 }Following is the query to display all documents from a collection with the help ... Read More

For this, use the $size operator. Let us first create a collection with documents −> db.checkIfListIsNotEmptyDemo.insertOne({"UserFriendGroup":["John", "David"]}); {    "acknowledged" : true,    "insertedId" : ObjectId("5cdd99e8bf3115999ed511f7") } > db.checkIfListIsNotEmptyDemo.insertOne({"UserFriendGroup":["Carol"]}); {    "acknowledged" : true,    "insertedId" : ObjectId("5cdd99e9bf3115999ed511f8") } > db.checkIfListIsNotEmptyDemo.insertOne({"UserFriendGroup":[]}); {    "acknowledged" : true,    "insertedId" : ObjectId("5cdd99ebbf3115999ed511f9") } > db.checkIfListIsNotEmptyDemo.insertOne({"UserFriendGroup":[null]}); {    "acknowledged" : true,    "insertedId" : ObjectId("5cdd99f2bf3115999ed511fa") } > db.checkIfListIsNotEmptyDemo.insertOne({"UserFriendGroup":[]}); {    "acknowledged" : true,    "insertedId" : ObjectId("5cdd99f6bf3115999ed511fb") }Following is the query to display all documents from a collection with the help of find() method −> db.checkIfListIsNotEmptyDemo.find().pretty();This will produce the following output −{   ... Read More

Let’s say you have saved the Login date of users. Now, you want the count of records for specific date only i.e. login date. For this, use $gte and $lt operator along with count(). Let us first create a collection with documents −> db.findDataByDateDemo.insertOne({"UserName":"John", "UserLoginDate":new ISODate("2019-01-31")}); {    "acknowledged" : true,    "insertedId" : ObjectId("5cdd8cd7bf3115999ed511ed") } > db.findDataByDateDemo.insertOne({"UserName":"Larry", "UserLoginDate":new ISODate("2019-02-01")}); {    "acknowledged" : true,    "insertedId" : ObjectId("5cdd8ce7bf3115999ed511ee") } > db.findDataByDateDemo.insertOne({"UserName":"Sam", "UserLoginDate":new ISODate("2019-05-02")}); {    "acknowledged" : true,    "insertedId" : ObjectId("5cdd8cf3bf3115999ed511ef") } > db.findDataByDateDemo.insertOne({"UserName":"David", "UserLoginDate":new ISODate("2019-05-16")}); {    "acknowledged" : true,    "insertedId" : ObjectId("5cdd8d00bf3115999ed511f0") } > db.findDataByDateDemo.insertOne({"UserName":"Carol", ... Read More

If you will try to use the method drop(), then it will delete all information about the collection. Indexing is fast. However, if you will use the method remove(), then it removes all records but keeps the collection and indexes.Let us check with the help of example.Using drop()Let us first create a collection with documents −> db.dropWorkingDemo.createIndex({"FirstName":1}); {    "createdCollectionAutomatically" : true,    "numIndexesBefore" : 1,    "numIndexesAfter" : 2,    "ok" : 1 } > db.dropWorkingDemo.insertOne({"FirstName":"John"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5cdd8742bf3115999ed511e9") }Following is the query to display all documents from a collection with the ... Read More

You can use $where operator for this. Let us first create a collection with documents −> db.sumOfFieldIsGreaterThanDemo.insertOne({"Price1":10, "Price2":50, "Price3":40}); {    "acknowledged" : true,    "insertedId" : ObjectId("5cdd84b8bf3115999ed511e6") } > db.sumOfFieldIsGreaterThanDemo.insertOne({"Price1":11, "Price2":1, "Price3":120}); {    "acknowledged" : true,    "insertedId" : ObjectId("5cdd84c6bf3115999ed511e7") } > db.sumOfFieldIsGreaterThanDemo.insertOne({"Price1":10, "Price2":9, "Price3":6}); {    "acknowledged" : true,    "insertedId" : ObjectId("5cdd84d2bf3115999ed511e8") }Following is the query to display all documents from a collection with the help of find() method −> db.sumOfFieldIsGreaterThanDemo.find();This will produce the following output −{ "_id" : ObjectId("5cdd84b8bf3115999ed511e6"), "Price1" : 10, "Price2" : 50, "Price3" : 40 } { "_id" : ObjectId("5cdd84c6bf3115999ed511e7"), "Price1" : ... Read More

You can use $elemMatch operator for this. Let us first create a collection with documents −> db.pushNewItemsDemo.insertOne(    {       "_id" :1,       "StudentScore" : 56,       "StudentOtherDetails" : [          {             "StudentName" : "John",             "StudentFriendName" : [                "Bob",                "Carol"             ]          },          {             "StudentName" : ... Read More

You need to use multi:true to update multiple documents. Let us first create a collection with documents −> db.multiUpdateDemo.insertOne({"ClientName":"John", "ClientAge":29}); {    "acknowledged" : true,    "insertedId" : ObjectId("5cda5bc0b50a6c6dd317adc8") } > db.multiUpdateDemo.insertOne({"ClientName":"Carol", "ClientAge":31}); {    "acknowledged" : true,    "insertedId" : ObjectId("5cda5bc1b50a6c6dd317adc9") } > db.multiUpdateDemo.insertOne({"ClientName":"John", "ClientAge":39}); {    "acknowledged" : true,    "insertedId" : ObjectId("5cda5bc3b50a6c6dd317adca") } > db.multiUpdateDemo.insertOne({"ClientName":"John", "ClientAge":41}); {    "acknowledged" : true,    "insertedId" : ObjectId("5cda5bc5b50a6c6dd317adcb") } > db.multiUpdateDemo.insertOne({"ClientName":"David", "ClientAge":35}); {    "acknowledged" : true,    "insertedId" : ObjectId("5cda5bc6b50a6c6dd317adcc") }Following is the query to display all documents from a collection with the help of find() method −> db.multiUpdateDemo.find().pretty();This ... Read More

You can use $set operator for this. Following is the syntax −db.yourCollectionName.update({"_id" : yourObjectId }, {$set: { "yourOuterFieldName.anyInnerFieldName": yourValue}});Let us first create a collection with documents −> db.pushNewKeyDemo.insertOne({"UserId":100, "UserDetails":{}}); {    "acknowledged" : true,    "insertedId" : ObjectId("5cda58f5b50a6c6dd317adbf") }Following is the query to display all documents from a collection with the help of find() method −> db.pushNewKeyDemo.find();This will produce the following output −{ "_id" : ObjectId("5cda58f5b50a6c6dd317adbf"), "UserId" : 100, "UserDetails" : { } }Following is the query to push new key element into subdocument of MongoDB −> db.pushNewKeyDemo.update({"_id" : ObjectId("5cda58f5b50a6c6dd317adbf")}, {$set: {    "UserDetails.UserName": "David Miller"}}); WriteResult({ "nMatched" : 1, ... Read More

You can use $pull operator to remove a string from an array. Let us first create a collection with documents −> db.removeAStringDemo.insertOne({"Score":[45, 67, 89, "John", 98, 99, 67]}); {    "acknowledged" : true,    "insertedId" : ObjectId("5cda5224b50a6c6dd317adbd") }Following is the query to display all documents from a collection with the help of find() method −> db.removeAStringDemo.find().pretty();This will produce the following output −{    "_id" : ObjectId("5cda5224b50a6c6dd317adbd"),    "Score" : [       45,       67,       89,       "John",       98,       99,       67    ] ... Read More