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$toHashedIndexKey (aggregation)

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  • Definition
  • Syntax
  • Example
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Definition

$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.

Note

Unlike hashed indexes, the $toHashedIndexKey aggregation operator does not 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.

Syntax

$toHashedIndexKey has the following syntax:

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

Example

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" } } }
   ]
 )

Example output:

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

Learn More

  • convertShardKeyToHashed()

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