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In MongoDB, projection allows you to display only specific fields from documents instead of returning all fields. To project a single column (field), use the find() method with a projection document that specifies which fields to include or exclude. Syntax db.collection.find({}, {fieldToShow: 1, _id: 0}); Or exclude unwanted fields: db.collection.find({}, {fieldToHide: 0, anotherField: 0}); Sample Data Let us first create a collection with documents − db.demo216.insertMany([ {"ClientName": "John", "ClientAge": 34}, {"ClientName": "Bob", "ClientAge": 32}, {"ClientName": "Mike", ... Read More
To insert a boolean field in MongoDB, use the true or false keywords directly in your document. MongoDB natively supports boolean data types, making it simple to store yes/no, on/off, or enabled/disabled states. Syntax db.collection.insertOne({ "fieldName": true, "anotherField": false }); Sample Data Let us create a collection with employee documents containing boolean fields − db.demo215.insertMany([ {"EmployeeDetails": [{"EmployeeName": "David", "isMarried": false, "Salary": 56000}]}, {"EmployeeDetails": [{"EmployeeName": "Bob", "isMarried": true, "Salary": 60000}]}, {"EmployeeDetails": [{"EmployeeName": "Chris", ... Read More
To aggregate multiple arrays into a single array in MongoDB, use the $concatArrays operator within the $project stage of an aggregation pipeline. This combines arrays from different fields into one unified array. Syntax db.collection.aggregate([ { $project: { combinedArray: { $concatArrays: ["$array1", "$array2", "$array3"] } ... Read More
The $addFields pipeline stage combined with the $filter operator allows you to add new fields or modify existing ones by filtering array elements based on specific conditions. Syntax db.collection.aggregate([ { $addFields: { "fieldName": { $filter: { input: ... Read More
To aggregate sum of values in a list of dictionaries for all documents, use $unwind to flatten the array, then $group with $sum operators to calculate totals by grouping field. Syntax db.collection.aggregate([ { $unwind: "$arrayField" }, { $group: { _id: "$arrayField.groupByField", "fieldSum1": { $sum: "$arrayField.field1" }, ... Read More
To find only a single document satisfying specific criteria in MongoDB, use the findOne() method. This method returns the first matching document from the collection, even if multiple documents satisfy the query criteria. Syntax db.collection.findOne(query, projection) Sample Data db.demo116.insertMany([ {"EmployeeId": 101, "EmployeeName": "John"}, {"EmployeeId": 102, "EmployeeName": "Bob"}, {"EmployeeId": 103, "EmployeeName": "David"}, {"EmployeeId": 102, "EmployeeName": "Mike"} ]); { "acknowledged": true, "insertedIds": [ ... Read More
To find the maximum score for duplicate Name values in MongoDB, use the aggregation pipeline with $group and $max operators. This groups documents by name and calculates the highest score for each group. Syntax db.collection.aggregate([ { $group: { _id: "$fieldName", maxScore: { $max: "$scoreField" } } } ]); ... Read More
To create views in MongoDB, use the createView() method. Views are read-only virtual collections that display data from underlying collections based on aggregation pipelines. Syntax db.createView( "viewName", "sourceCollection", [aggregationPipeline] ) Sample Data Let us create a collection with sample documents ? db.demo113.insertMany([ { _id: 1, StudentId: "101", "Details": { Name: "Chris", Age: 21 }, Subject: "MySQL" }, { _id: 2, StudentId: "102", "Details": { Name: "Alice", Age: 20 }, Subject: "MongoDB" }, ... Read More
To update a single field in a capped collection in MongoDB, use the updateOne() or updateMany() method with the $set operator. Capped collections allow field updates but do not permit operations that would increase document size. Syntax db.collection.updateOne( { "field": "matchValue" }, { $set: { "field": "newValue" } } ); Create Sample Capped Collection First, create a capped collection with size and document limits ? db.createCollection("Demo112", { capped : true, size : 14, max : 3 } ); { "ok" : ... Read More
To slice an array inside another array in MongoDB, use the aggregate() method with $addFields, $map, and $slice operators. This allows you to limit the number of elements returned from nested arrays. Syntax db.collection.aggregate([ { $addFields: { "arrayField": { $map: { "input": "$arrayField", ... Read More