$toLower (aggregation)
Definition
$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""
.
Behavior
$toLower
only has a well-defined behavior for strings of ASCII characters.
Example
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: "" }