Big Data Analytics Articles - Page 151 of 167

The _id in MongoDB is a field, which is mandatory. In MongoDB, each document stored in a collection requires a unique _id field that acts as a primary key. Following is the syntax to get the array of all the ids i.e. _id in MongoDBdb.yourCollectionName.find({ _id : { $in : [yourValue1, yourValue2, yourValue3, .......N] } } );Let us first implement the following query to create a collection with documents> db.selectInWhereIdDemo.insertOne({"_id":23}); { "acknowledged" : true, "insertedId" : 23 } > db.selectInWhereIdDemo.insertOne({"_id":28}); { "acknowledged" : true, "insertedId" : 28 } > db.selectInWhereIdDemo.insertOne({"_id":45}); { "acknowledged" : true, "insertedId" : 45 } > db.selectInWhereIdDemo.insertOne({"_id":75}); ... Read More

In MongoDB, there is no concept of columns since MongoDB is schema-less and does not contain tables. It contains the concept of collections and a collection has different types of documents to store items.Let us see the syntax −db.yourCollectionName.insertOne({“YourFieldName”:yourValue, “yourFieldName”:”yourValue”, .......N});If you want a single record from a collection, you can use findOne() and in order to get all records from the collection, you can use find().The syntax is as follows −db.yourCollectionName.findOne(); //Get Single Record db.yourCollectionName.find(); // Get All RecordTo understand the above syntax, let us create a collection with the document. The query to create a collection with a ... Read More

You can switch from one database to another using the use command. Here, we are using the collection in the “test” database. Let us insert that collection in another database with the name “sample”.To understand further, let us create a collection with the document. The query to create a collection with a document is as follows −> db.insertOneRecordDemo.insertOne({"UserName":"Larry", "UserAge":23}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c9534de16f542d757e2b452") } > db.insertOneRecordDemo.insertOne({"UserName":"Chris", "UserAge":26}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c9534e816f542d757e2b453") } > db.insertOneRecordDemo.insertOne({"UserName":"David", "UserAge":25}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c9534f116f542d757e2b454") }Display all documents from a collection ... Read More

MongoDB order the docs in one collection with the help of a $natural operator. It stores the document as it is when we get from find(). The default order is $natural. Let us now see the syntax −db.yourCollectionName.find().sort({ "$natural": 1 });To understand the above syntax, let us create a collection with the document. The query to create a collection with a document is as follows −> db.orderDocsDemo.insertOne({"UserScore":87}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c9531a316f542d757e2b44b") } > db.orderDocsDemo.insertOne({"UserScore":98}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c9531a816f542d757e2b44c") } > db.orderDocsDemo.insertOne({"UserScore":99}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c9531b216f542d757e2b44d") ... Read More

First of all, you need to get your collection with the help of getCollectionNames().The database name is “test”. Let us loop through all MongoDB collections and execute the query. The query is as follows −> db.getCollectionNames().forEach(function(collectioNameDemo) ... {    ... var nextDemo = db[(collectioNameDemo) ].find().sort({_id:-1}).limit(1);    ... if (nextDemo.hasNext())    ... {       ... printjson(nextDemo.next()._id.getTimestamp());    ... } ... });The following is the output −ISODate("2019-02-21T18:52:43Z") ISODate("2019-03-19T17:49:00Z") ISODate("2019-03-06T15:40:12Z") ISODate("2019-03-15T16:31:50Z") ISODate("2019-02-21T15:40:52Z") ISODate("2019-03-06T06:14:37Z") ISODate("2019-02-21T19:29:15Z") ISODate("2019-03-15T13:35:33Z") ISODate("2019-03-14T21:13:58Z") ISODate("2019-03-18T22:02:54Z") ISODate("2019-03-22T18:01:45Z") ISODate("2019-03-06T16:21:14Z") ISODate("2019-02-20T15:04:32Z") ISODate("2019-03-06T07:45:42Z") ISODate("2019-03-19T12:33:17Z") ISODate("2019-03-20T21:39:21Z") ISODate("2019-03-15T16:44:26Z") ISODate("2019-03-22T06:20:45Z") ISODate("2019-02-21T16:40:55Z") ISODate("2019-02-21T12:45:20Z") ISODate("2019-03-06T16:05:48Z") ISODate("2019-03-06T16:00:08Z") ISODate("2019-02-28T12:43:56Z") ISODate("2019-03-20T22:11:41Z") ISODate("2019-03-06T05:56:45Z") ISODate("2019-03-06T07:34:12Z") ISODate("2019-03-14T21:00:16Z") ISODate("2019-02-28T10:33:39Z") ISODate("2019-03-06T05:11:10Z") ISODate("2019-02-28T09:44:28Z") ISODate("2019-03-06T10:13:22Z") ISODate("2019-03-17T21:35:26Z")Read More

To understand the query on list field, and/or, you can create a collection with documents.The query to create a collection with a document is as follows −> db.andOrDemo.insertOne({"StudentName":"Larry", "StudentScore":[33, 40, 50, 60, 70]}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c9522d316f542d757e2b444") } > db.andOrDemo.insertOne({"StudentName":"Larry", "StudentScore":[87, 67, 79, 98, 90]}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c95230916f542d757e2b445") }Display all documents from a collection with the help of find() method. The query is as follows −> db.andOrDemo.find().pretty();The following is the output −{    "_id" : ObjectId("5c9522d316f542d757e2b444"),    "StudentName" : "Larry",    "StudentScore" : [       33,   ... Read More

You can use $unset as well as $pull operator with an update to delete the nth element of an array.Let us create a collection with a document. The query to create a collection with a document is as follows −> db.getNThElementDemo.insertOne({"UserName":"John", "UserAge":23, "ListOfFriends":["Carol", "Sam", "Mike", "Bob"]}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c94ee7516f542d757e2b43e") } > db.getNThElementDemo.insertOne({"UserName":"David", "UserAge":21, "ListOfFriends":["Chris", "Robert"]}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c94eeaa16f542d757e2b43f") }Display all documents from a collection with the help of find() method. The query is as follows −> db.getNThElementDemo.find().pretty();The following is the output −{    "_id" : ObjectId("5c94ee7516f542d757e2b43e"),    "UserName" ... Read More

To identify the last document from MongoDB find() result set, you can use sort() in descending order. The syntax is as follows −db.yourCollectionName.find().sort( { _id : -1 } ).limit(1).pretty();To understand the above syntax, let us create a collection with the document. The query to create a collection with a document is as follows −> db.identifyLastDocuementDemo.insertOne({"UserName":"Larry", "UserAge":24, "UserCountryName":"US"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c94a2ff4cf1f7a64fa4df57") } > db.identifyLastDocuementDemo.insertOne({"UserName":"Chris", "UserAge":21, "UserCountryName":"UK"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c94a3094cf1f7a64fa4df58") } > db.identifyLastDocuementDemo.insertOne({"UserName":"David", "UserAge":25, "UserCountryName":"AUS"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c94a3174cf1f7a64fa4df59") } > db.identifyLastDocuementDemo.insertOne({"UserName":"Sam", "UserAge":26, "UserCountryName":"US"}); { ... Read More

In order to check the current configuration of MongoDB, you can use getCmdLineOpts. The query is as follows −> db._adminCommand( {getCmdLineOpts: 1});The following is the output −{ "argv" : [ "mongod" ], "parsed" : { }, "ok" : 1 }In order to check live settings, you can use the below query −> db._adminCommand({getParameter:"*"});The following is the output &minus{    "AsyncRequestsSenderUseBaton" : true,    "KeysRotationIntervalSec" : 7776000,    "ShardingTaskExecutorPoolHostTimeoutMS" : 300000,    "ShardingTaskExecutorPoolMaxConnecting" : 2,    "ShardingTaskExecutorPoolMaxSize" : -1,    "ShardingTaskExecutorPoolMinSize" : 1,    "ShardingTaskExecutorPoolRefreshRequirementMS" : 60000,    "ShardingTaskExecutorPoolRefreshTimeoutMS" : 20000,    "TransactionRecordMinimumLifetimeMinutes" : 30,    "adaptiveServiceExecutorIdlePctThreshold" : 60,    "adaptiveServiceExecutorMaxQueueLatencyMicros" ... Read More

You can achieve pagination with the help of limit() and skip() in MongoDB.To understand the concept, let us create a collection with the document. The query to create a collection with a document is as follows −> db.paginationDemo.insertOne({"CustomerName":"Chris", "CustomerAge":23}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c949de44cf1f7a64fa4df52") } > db.paginationDemo.insertOne({"CustomerName":"Robert", "CustomerAge":26}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c949df14cf1f7a64fa4df53") } > db.paginationDemo.insertOne({"CustomerName":"David", "CustomerAge":24}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c949dfc4cf1f7a64fa4df54") } > db.paginationDemo.insertOne({"CustomerName":"Carol", "CustomerAge":28}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c949e3e4cf1f7a64fa4df55") } > db.paginationDemo.insertOne({"CustomerName":"Bob", "CustomerAge":29}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c949e474cf1f7a64fa4df56") ... Read More