MongoDB $toLower Operator

MongoDB $toLower operator converts the given string to lowercase.

$toLower Operator in MongoDB

The $toLower operator in MongoDB is used in aggregation pipeline stages to convert a string to lowercase and return it.

This operator takes an expression as an input, this expression should resolve into a string for proper functioning. The $toLower operator in MongoDB has a well-defined behavior for ASCII characters.

Syntax

{ $toLower: <expression> }

Here, the argument passed in this operator can be any valid expression until it resolves to a string. If the entered argument resolves to null, then this operator will return an empty string ” “.

MongoDB $toLower Operator Examples

To understand it better, let’s look at some examples of MongoDB $toLower Operator.

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.

Using $toLower Operator Example

In this example, we are going to convert the value of the department field in lowercase.

Query:

db.employee.aggregate([
... {$match: {"name.first": "Aman"}},
... {$project: {dept: {$toLower: "$department"}}}])

Output:

Using $toLower Operator in embedded documents Example

In this example, we are going to convert the value of the name.first field in lowercase.

db.employee.aggregate([
... {$match: {department: "Development"}},
... {$project: {name: {$toLower: "$name.first"}}}])

KeyTakeAways About MongoDB $toLower Operator

• The MongoDB $toLower operator in is used in the aggregation pipeline stages to convert a string to lowercase and return the result.
• It accepts an expression as an argument, which can be any expression that resolves to a string.
• If the argument provided to $toLower resolves to null, it returns an empty string.
• $toLower only has a well-defined behavior for strings of ASCII characters.
• The $toLower operator is designed for use within the aggregation framework and is not used directly in update operations to modify documents in a collection.