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$toLower (aggregation)

$toLower

Converts a string to lowercase, returning the result.

$toLower has the following syntax:

{ $toLower: <expression> }

The argument can be any expression as long as it resolves to a string. For more information on expressions, see Expressions.

If the argument resolves to null, $toLower returns an empty string "".

$toLower only has a well-defined behavior for strings of ASCII characters.

Consider a inventory collection with the following documents:

db.inventory.insertMany( [
{ _id: 1, item: "ABC1", quarter: "13Q1", description: "PRODUCT 1" },
{ _id: 2, item: "abc2", quarter: "13Q4", description: "Product 2" },
{ _id: 3, item: "xyz1", quarter: "14Q2", description: null }
] )

The following operation uses the $toLower operator return lowercase item and lowercase description value:

db.inventory.aggregate(
[
{
$project:
{
item: { $toLower: "$item" },
description: { $toLower: "$description" }
}
}
]
)

The operation returns the following results:

{ _id: 1, item: "abc1", description: "product 1" }
{ _id: 2, item: "abc2", description: "product 2" }
{ _id: 3, item: "xyz1", description: "" }

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