$toLower (aggregation)

定義

$toLower

Converts a string to lowercase, returning the result.

$toLowerの構文は次のとおりです。

{ $toLower: <expression> }

The argument can be any 式 as long as it resolves to a string. For more information on expressions, see 式演算子.

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

動作

$toLowerは ASCII 文字の string に対してのみ、明確に定義された動作を行います。

例

以下のドキュメントを持つinventoryコレクションを考えてみましょう。

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" }
         }
     }
   ]
)

この操作は次の結果を返します。

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