$toLower (aggregation)
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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 Expression Operators.
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:
{ "_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" : "" }