MongoDB $add Operator
MongoDB provides different types of arithmetic expression operators that are used in the aggregation pipeline stages and $add operator is one of them. This operator is used to add numbers or dates. If $add operator adds date, then it will treat other arguments as milliseconds and add to the specified date.
Syntax:
{ $add: [ <Expression1>, <Expression2>, ... <ExpressionN>] }
Here, the Expression must be a valid expression like numbers or a date.
Examples:
In the following examples, we are working with:
Database: w3wiki
Collection: Employee
Document: four documents that contain the details of the employees in the form of field-value pairs.
Adding numbers using $add operator:
In this example, we are going to find the total salary of every employee in the development department.
db.Employee.aggregate([{$match: {department: "Development"}}, ... {$project: {name: 1, tSalary: {$add: ["$firstSalary", "$secondSalary"]}}}])
Adding numbers in the embedded document using $add operator:
In this example, we are going to find a total of three months’ salary of the employee in the HR department.
db.Employee.aggregate([{$match: {department: "HR"}}, ... {$project: {name: 1, tSalary: {$add: ["$salary.firstMonth", "$salary.secondMonth", "$salary.thirdMonth"]}}}])
Adding date using $add operator:
In this example, we are going to extend the last date of the project by adding 5 days (i.e, 5*24*60*60000) in the projectEndDate field of the testing department.
db.Employee.aggregate([{$match: {department: "Testing"}}, ... {$project: {extendprojectDate: {$add: ["$projectEndDate", 5*24*60*60000]}}}])
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