Introduction to MongoDB $mod Operator

In MongoDB, the $mod operator is used to calculate the remainder of a given number and compare it with a specified value.

Syntax

The $mod operator has the following format:

{
  field: {
    $mod: [divisor, remainder]
  }
}

Where field is the field to be calculated, divisor is the divisor, and remainder is the remainder.

Use Cases

The $mod operator is typically used to query records with a specific remainder, such as querying for even or odd records.

Examples

Example 1

Assuming we have a collection named products that contains the following documents:

{ "_id" : 1, "name" : "Product A", "price" : 10 }
{ "_id" : 2, "name" : "Product B", "price" : 15 }
{ "_id" : 3, "name" : "Product C", "price" : 20 }
{ "_id" : 4, "name" : "Product D", "price" : 25 }
{ "_id" : 5, "name" : "Product E", "price" : 30 }

We can use the $mod operator to find products with even prices:

db.products.find({ price: { $mod: [2, 0] } })

The above query will return the following results:

{ "_id" : 2, "name" : "Product B", "price" : 15 }
{ "_id" : 4, "name" : "Product D", "price" : 25 }

Example 2

Assuming we have a collection named students that contains the following documents:

{ "_id" : 1, "name" : "Alice", "score" : 85 }
{ "_id" : 2, "name" : "Bob", "score" : 90 }
{ "_id" : 3, "name" : "Charlie", "score" : 95 }
{ "_id" : 4, "name" : "David", "score" : 80 }
{ "_id" : 5, "name" : "Emma", "score" : 75 }

We can use the $mod operator to find students with scores that are multiples of 5:

db.students.find({ score: { $mod: [5, 0] } })