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Big Data Analytics Articles
Page 29 of 135
Update salary field value with 10 percent of each employee in MongoDB
To update salary field values with a 10 percent increase for each employee in MongoDB, use the $mul operator with a multiplier of 1.1. This operator multiplies the existing field value by the specified number. Syntax db.collection.update( { query }, { $mul: { fieldName: multiplier } }, { multi: true } ); Create Sample Data Let us first create a collection with employee documents ? db.demo417.insertMany([ {"EmployeeName": "Chris", "EmployeeSalary": 500}, {"EmployeeName": "Mike", ...
Read MoreHow to select specific columns in MongoDB query?
To select specific columns in MongoDB, use projection in the find() method. Set fields to 1 to include them or 0 to exclude them. You can hide unwanted columns by setting them to 0, showing only the desired fields. Syntax db.collection.find(query, projection) // Include specific fields db.collection.find({}, {field1: 1, field2: 1}) // Exclude specific fields db.collection.find({}, {field1: 0, field2: 0}) Sample Data db.demo415.insertMany([ {"ClientName": "Robert", "ClientCountryName": "US"}, {"ClientName": "David", "ClientCountryName": "UK"}, {"ClientName": "Bob", "ClientCountryName": "AUS"} ]); ...
Read MoreFind by _id on an array of objects in MongoDB database?
To find by _id on an array of objects in MongoDB, use the aggregation framework with $unwind and $match operators. This approach is more effective than using find() when working with nested array elements. Syntax db.collection.aggregate([ { $unwind: "$arrayField" }, { $match: { "arrayField.field": "value" } } ]); Sample Data db.demo414.insertOne({ "_id": "110", "details": [ { "StudentName": ...
Read MoreIs it possible to exclude nested fields in MongoDB with a wildcard?
Yes, you can exclude nested fields with a wildcard pattern in MongoDB using the aggregation pipeline. This technique uses $objectToArray and $arrayToObject operators to transform nested objects, exclude specific fields, and reconstruct the document. Syntax db.collection.aggregate([ { $project: { "nestedField": { $objectToArray: "$nestedField" } } }, { $project: { "nestedField.v.fieldToExclude": 0 } }, { $project: { "nestedField": { $arrayToObject: "$nestedField" } } } ]); Sample Data db.demo413.insertOne({ "_id": "101", "details": { ...
Read MoreUpdate an array of strings nested within an array of objects in MongoDB
To update an array of strings nested within an array of objects in MongoDB, use the $pull operator with the positional all operator $[] to remove elements from nested arrays across all array elements. Syntax db.collection.updateMany( { query }, { $pull: { "arrayField.$[].nestedArray": "valueToRemove" } } ); Sample Data db.demo412.insertOne({ "Information1": [ { "Information2": [ ...
Read MoreHow to get only values in arrays with MongoDB aggregate?
To get only values from arrays in MongoDB aggregate operations, use the $map operator within $project to transform array elements and extract specific field values into a new array structure. Syntax db.collection.aggregate([ { $project: { arrayField: { $map: { ...
Read MoreHow do I remove elements not matching conditions in MongoDB?
To remove elements not matching conditions in MongoDB, use the $pull operator combined with query conditions. The $pull operator removes all array elements that match the specified condition. Syntax db.collection.updateMany( { "arrayField": { "$elemMatch": { "field": { "$ne": "value" } } } }, { "$pull": { "arrayField": { "field": { "$ne": "value" } } } } ); Sample Data Let us create a collection with documents ? db.demo410.insertOne({ details: [ {isMarried: false}, ...
Read MoreUnderstanding MongoDB Query Plan
To understand how MongoDB executes queries, use the explain() method. Query plans show the execution strategy, including which indexes are used and performance statistics for query optimization. Syntax db.collection.explain().find(query); db.collection.explain("executionStats").find(query); db.collection.explain("allPlansExecution").find(query); Sample Data Let us create a collection with documents and an index ? db.demo408.insertMany([ {"Value": 50}, {"Value": 20}, {"Value": 45}, {"Value": 35} ]); { "acknowledged": true, "insertedIds": [ ...
Read MoreHow to create MongoDB user on existing database with correct role?
To create a new user in MongoDB, use the createUser() method on an existing database. This allows you to assign specific roles and authentication mechanisms to control user permissions. Syntax db.createUser({ user: "username", pwd: "password", roles: [ { role: "roleName", db: "databaseName" } ], mechanisms: ["SCRAM-SHA-256"] }); Example: Create User with readWrite Role Create a user named "John" with readWrite permissions on the test database ? ...
Read MoreHow to use arrays as filters by querying subdocuments in MongoDB?
To use arrays as filters when querying subdocuments in MongoDB, use the $setIsSubset operator within an aggregation pipeline. This operator checks if one array is a subset of another, making it useful for filtering array elements based on specific values. Syntax db.collection.aggregate([ { $project: { "arrayField": { $filter: { input: "$arrayField", ...
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