MongoDB $multiply Operator

In MongoDB, the $multiply operator is a powerful tool used in aggregation pipelines to perform multiplication operations. This operator takes one or more expressions as arguments and multiplies them to produce a result.

In this article, we will explain the MongoDB $multiply operator, its syntax, usage, and practical examples to help us master its functionality.

What is MongoDB $multiply Operator?

The MongoDB $multiply operator is used to multiply two or more numeric values or expressions together. It returns the result of multiplying all provided values and can be used in the aggregation pipeline for advanced data manipulation and transformation. This operator is essential for performing arithmetic operations such as calculating totals, adjusting values, or performing mathematical computations directly within our MongoDB queries.

Syntax

{ $multiply: [ <expression1>, <expression2>, ... <expressionN> ] }

Parameters:

• Expression1, Expression2, ..., ExpressionN: These are the values or fields you want to multiply. They must resolve to numeric values.
• The $multiply operator operates on numeric expressions and will return an error if any expression does not resolve to a number.

Examples of MongoDB $multiply Operator

Here are some practical examples of using the $multiply operator in MongoDB to perform calculations in the aggregation pipeline. In the following examples, we are working with:

• Database: GeeksforGeeks
• Collection: employee
• Document: three documents that contain the details of the employees in the form of field-value pairs.

Example 1: Multiply Using $multiply Operator

Here are some practical examples of using the $multiply operator in MongoDB to perform calculations in the aggregation pipeline. In this example, we are going to multiply the salary of the development department's employees by 2.

Query:

db.employee.aggregate([{$match: {department: "Development"}},
... {$project: {name: 1, newSalary: {$multiply: ["$salary", 2]}}}])

Output:

Explanation:

• The query selects employees from the "Development" department.
• It then multiplies the salary field by 2 using the $multiply operator.
• The result is stored in the newSalary field.

Example 2: Multiply Using $multiply Operator in the Embedded Document

MongoDB allows us to use $multiply on fields within embedded documents. This example multiplies the salary of employees in the "HR" department, where the salary is stored inside an embedded document.

Query:

db.employee.aggregate([{$match: {department: "HR"}},
... {$project: {name: 1, newSalary: {$multiply: ["$details.salary", 3]}}}])

Output:

Explanation:

• The salary field is embedded within the details subdocument.
• The $multiply operator multiplies the embedded salary by 3, creating a new newSalary field.

Example 3: Add a Fixed Number to the Array with the Output

To add a fixed number to the array perfoPoint for all documents in the employee collection, we can use the $inc operator. Here's how we can do it:

Query:

db.employee.updateMany({}, { $inc: { perfoPoint: 2.5 } })

Output:

{
    "acknowledged": true,
    "matchedCount": 3,
    "modifiedCount": 3
}

How to Combine $multiply with Other Operators

The $multiply operator can be combined with other MongoDB operators, such as $add, $divide, or $subtract, to perform more complex calculations. For example, we could calculate a bonus by multiplying a percentage increase with an employee's salary and then adding a fixed value.

Example combining $multiply with $add:

db.employee.aggregate([
  { $project: { 
      name: 1, 
      totalSalary: { $add: [{ $multiply: ["$salary", 1.1] }, 1000] } 
  } }
])

This query calculates a 10% salary increase and then adds a $1000 bonus.

Benefits of Using the $multiply Operator in MongoDB

1. Perform Complex Calculations

The $multiply operator allows you to perform arithmetic operations in MongoDB aggregation pipelines, saving time by eliminating the need for complex post-processing in your application.

2. Flexible Arithmetic Operations

You can multiply numeric fields, constants, or values from embedded documents, offering great flexibility in manipulating your data directly within MongoDB.

3. Efficient Data Transformations

The $multiply operator is ideal for transforming data in real-time, whether adjusting salaries, calculating totals, or making adjustments to other numerical values.

Conclusion

The MongoDB $multiply operator is an indispensable tool for performing numeric operations within the aggregation pipeline. Whether we’re multiplying field values, adjusting embedded documents, or performing complex calculations, this operator streamlines arithmetic operations directly within our queries. By using $multiply, MongoDB developers can manipulate data efficiently, transforming raw data into actionable insights without additional processing steps.