$toHashedIndexKey (aggregation)

定義

$toHashedIndexKey

Computes and returns the hash value of the input expression using the same hash function that MongoDB uses to create a hashed index. A hash function maps a key or string to a fixed-size numeric value.

注意

Unlike hashed indexes, the $toHashedIndexKey aggregation operator does ではない account for collation. This means the operator can produce a hash that does not match that of a hashed index based on the same data.

構文

$toHashedIndexKeyの構文は次のとおりです。

{ $toHashedIndexKey: <key or string to hash> }

例

You can use $toHashedIndexKey to compute the hashed value of a string in an aggregation pipeline. This example computes the hashed value of the string "string to hash":

db.aggregate(
   [
      { $documents: [ { val: "string to hash" } ] },
      { $addFields: { hashedVal: { $toHashedIndexKey: "$val" } } }
   ]
 )

出力例:

[ { val: 'string to hash', hashedVal: Long("763543691661428748") } ]

詳細

• convertShardKeyToHashed()