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Big Data Analytics Articles
Page 106 of 135
Projection result as an array of selected items in MongoDB?
Use the distinct() for this, since it finds the distinct values for a specified field across a single collection or view and returns the results in an array.Let us first create a collection with documents −> db.projectionListDemo.insertOne({"_id":"1", "Subject":["MongoDB", "MySQL", "Java"]}); { "acknowledged" : true, "insertedId" : "1" } > db.projectionListDemo.insertOne({"_id":"2", "Subject":["MongoDB", "C", "C++"]}); { "acknowledged" : true, "insertedId" : "2" } > db.projectionListDemo.insertOne({"_id":"3", "Subject":["Java", "Python"]}); { "acknowledged" : true, "insertedId" : "3" }Display all documents from a collection with the help of find() method −> db.projectionListDemo.find().pretty();Output{ "_id" : "1", "Subject" : [ "MongoDB", "MySQL", "Java" ] } { "_id" : ...
Read MoreMongoDB query to find data from an array inside an object?
Let us first create a collection with documents −> db.findDataDemo.insertOne( { "_id": new ObjectId(), "CustomerName":"John", "CustomerDetails" : { "CountryName" : [ "AUS" ], "isMarried" : [ false ] } } ); { "acknowledged" : true, "insertedId" : ObjectId("5cefa5eeef71edecf6a1f6a5") } > db.findDataDemo.insertOne( { "_id": new ObjectId(), "CustomerName":"Carol", ...
Read MoreMongoDB query to get last inserted document?
To get last inserted document, use sort() along with limit(1).Let us first create a collection with documents −> db.getLastInsertedDocument.insertOne({"Name":"John"}); { "acknowledged" : true, "insertedId" : ObjectId("5cefb17eef71edecf6a1f6a8") } > db.getLastInsertedDocument.insertOne({"Name":"Chris"}); { "acknowledged" : true, "insertedId" : ObjectId("5cefb181ef71edecf6a1f6a9") } > db.getLastInsertedDocument.insertOne({"Name":"Robert"}); { "acknowledged" : true, "insertedId" : ObjectId("5cefb185ef71edecf6a1f6aa") }Display all documents from a collection with the help of find() method −> db.getLastInsertedDocument.find();Output{ "_id" : ObjectId("5cefb17eef71edecf6a1f6a8"), "Name" : "John" } { "_id" : ObjectId("5cefb181ef71edecf6a1f6a9"), "Name" : "Chris" } { "_id" : ObjectId("5cefb185ef71edecf6a1f6aa"), "Name" : "Robert" }Following is the query to get last inserted document −> db.getLastInsertedDocument.find({}).sort({_id:-1}).limit(1);Output{ "_id" ...
Read MoreDisplay the last two values from field with MongoDB
Let us first create a collection with documents −> db.numberOfValuesDemo.insertOne({"Values":[100,200,300,900,1000,98]}); { "acknowledged" : true, "insertedId" : ObjectId("5cefb736ef71edecf6a1f6ab") }Display all documents from a collection with the help of find() method −> db.numberOfValuesDemo.find().pretty();Output{ "_id" : ObjectId("5cefb736ef71edecf6a1f6ab"), "Values" : [ 100, 200, 300, 900, 1000, 98 ] }Following is the query to get the last two values.Here, we have used -ve sign under $slice −> db.numberOfValuesDemo.find({},{ "Values": { "$slice": -2 } } );Output{ "_id" : ObjectId("5cefb736ef71edecf6a1f6ab"), "Values" : [ 1000, 98 ] }
Read MoreLimit number of values in a field using MongoDB?
To limit number of values in a field, use $slice operator.Let us first create a collection with documents −> db.numberOfValuesDemo.insertOne({"Values":[100,200,300,900,1000,98]}); { "acknowledged" : true, "insertedId" : ObjectId("5cefb736ef71edecf6a1f6ab") }Display all documents from a collection with the help of find() method −> db.numberOfValuesDemo.find().pretty();Output{ "_id" : ObjectId("5cefb736ef71edecf6a1f6ab"), "Values" : [ 100, 200, 300, 900, 1000, 98 ] }Following is the query to limit number of values in a field using MongoDB −> db.numberOfValuesDemo.find({},{ "Values": { "$slice": 2 } } );Output{ "_id" : ObjectId("5cefb736ef71edecf6a1f6ab"), "Values" : [ 100, 200 ] }
Read MoreMongoDB query to select one field if the other is null and the first field if both are not null?
For this, use $ifNull operatorLet us first create a collection with documents −> dbquerySelectDemoinsertOne({"Value1":10, "Value2":null}); { "acknowledged" : true, "insertedId" : ObjectId("5cefc0ceef71edecf6a1f6b6") } > dbquerySelectDemoinsertOne({"Value1":null, "Value2":30}); { "acknowledged" : true, "insertedId" : ObjectId("5cefc0d7ef71edecf6a1f6b7") } > dbquerySelectDemoinsertOne({"Value1":60, "Value2":40}); { "acknowledged" : true, "insertedId" : ObjectId("5cefc0e2ef71edecf6a1f6b8") }Display all documents from a collection with the help of find() method −> dbquerySelectDemofind()pretty();Output{ "_id" : ObjectId("5cefc0ceef71edecf6a1f6b6"), "Value1" : 10, "Value2" : null } { "_id" : ObjectId("5cefc0d7ef71edecf6a1f6b7"), "Value1" : null, "Value2" : 30 } { "_id" : ObjectId("5cefc0e2ef71edecf6a1f6b8"), "Value1" : 60, ...
Read MoreIs it possible to return a list of specific values from a MongoDB query?
Yes, using map(). Let us first create a collection with documents −> dblistOfSpecificValuesDemoinsertOne({"StudentName":"John"}); { "acknowledged" : true, "insertedId" : ObjectId("5cefcc8fef71edecf6a1f6bb") } > dblistOfSpecificValuesDemoinsertOne({"StudentName":"Chris"}); { "acknowledged" : true, "insertedId" : ObjectId("5cefcc94ef71edecf6a1f6bc") } > dblistOfSpecificValuesDemoinsertOne({"StudentName":"Robert"}); { "acknowledged" : true, "insertedId" : ObjectId("5cefcc98ef71edecf6a1f6bd") } > dblistOfSpecificValuesDemoinsertOne({"StudentName":"David"}); { "acknowledged" : true, "insertedId" : ObjectId("5cefcc9cef71edecf6a1f6be") }Following is the query to display all documents from a collection with the help of find() method −> dblistOfSpecificValuesDemofind();Output{ "_id" : ObjectId("5cefcc8fef71edecf6a1f6bb"), "StudentName" : "John" } { "_id" : ObjectId("5cefcc94ef71edecf6a1f6bc"), "StudentName" : "Chris" } { "_id" : ObjectId("5cefcc98ef71edecf6a1f6bd"), "StudentName" : "Robert" } ...
Read MoreUpdate key value where another key equals some value in MongoDB?
Use $elemMatch fir this with $setLet us first create a collection with documents −> dbkeyValueDemoinsertOne( { "_id" : new ObjectId(), "CustomerDetails" : [ { "Name" : "Chris", "Age" :24, }, { "Name" : "Robert", "Age" :29, }, { "Name" : "David", ...
Read MoreSpecify return format in MongoDB to return the values as an array?
Use aggregation for this and add the values to an array using the $group and $addToSet operatorLet us first create a collection with documents −> dbspecifyReturnFormatDemoinsertOne({"Subject":"MongoDB"}); { "acknowledged" : true, "insertedId" : ObjectId("5cefd364ef71edecf6a1f6c0") } > dbspecifyReturnFormatDemoinsertOne({"Subject":"MySQL"}); { "acknowledged" : true, "insertedId" : ObjectId("5cefd369ef71edecf6a1f6c1") } > dbspecifyReturnFormatDemoinsertOne({"Subject":"SQL Server"}); { "acknowledged" : true, "insertedId" : ObjectId("5cefd36fef71edecf6a1f6c2") }Following is the query to display all documents from a collection with the help of find() method −> dbspecifyReturnFormatDemofind();Output{ "_id" : ObjectId("5cefd364ef71edecf6a1f6c0"), "Subject" : "MongoDB" } { "_id" : ObjectId("5cefd369ef71edecf6a1f6c1"), "Subject" : "MySQL" } { "_id" : ObjectId("5cefd36fef71edecf6a1f6c2"), "Subject" : ...
Read MoreCompare multiple properties in MongoDB?
To compare multiple properties, use the $where operator. Let us first create a collection with documents −> dbcomparingMultiplePropertiesDemoinsertOne({"Values":[10, 70, 60]}); { "acknowledged" : true, "insertedId" : ObjectId("5cf228fcb64a577be5a2bc0a") }Following is the query to display all documents from a collection with the help of find() method −> dbcomparingMultiplePropertiesDemofind()pretty();This will produce the following document −{ "_id" : ObjectId("5cf228fcb64a577be5a2bc0a"), "Values" : [ 10, 70, 60 ] }Case 1: If condition becomes true then you will get an array otherwise nothing will get displayed Following is the query to compare multiple ...
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