Current State:

MongoDB currently lacks a native $hash operator in the aggregation/query language. While certain helpers like convertShardKeyToHashed or $toHashedIndexKey exist, they are limited in scope:

• Not available as true query operators (e.g., inaccessible from MongoDB drivers).
• Return Long values, which aren’t suitable for use cases like generating ObjectId-compatible hashes.
• Not guaranteed to be stable across versions — limiting their use in persisted or version-sensitive scenarios.
• Lack of flexibility in algorithm choice (e.g., MD5 only).

The deprecation of $function further limits users’ ability to implement custom hashing via JS.

Impact:

Developers working with large datasets (dozens of GB) are unable to:

• Perform deterministic hashing inside MongoDB queries/aggregations.
• Use hash values as _id or compact document identifiers for deduplication, fingerprinting, or efficient lookups.
• Build predictable, cross-version-stable hashes within MQL.
• Avoid extra client-side computation or complex workarounds involving bitwise operations, slow modulo arithmetic, or full client-side aggregation to generate a hash.

Additionally, non-driver-accessible helpers lead to more application logic overhead and additional round-trips to the database, hurting latency and performance.

Potential Future State:

Introduce a first-class $hash operator in the MongoDB query and aggregation language:

{
  $hash: {
    algorithm: "SHA384",  // e.g., SHA256, SHA512, etc.
    data: <expression>,
    // Optional: key (for HMAC support in the future)
  }
}

• Returns a hexadecimal string (or binary, or ObjectId-compatible format).
• Deterministic and version-stable.
• Accepts MQL expressions for the input.
• Could include support for standard NIST algorithms (see: https://csrc.nist.gov/projects/hash-functions).

Initial implementation could focus on non-HMAC hashes only to reduce scope.

Additional Info or Links:

• Use case: compact storage of hash-based _ids for large datasets.
• Common workaround (not ideal): https://stackoverflow.com/questions/67426169/how-do-you-convert-a-hexadecimal-string-into-a-number-in-mongodb
• NIST-approved algorithms list: https://csrc.nist.gov/projects/hash-functions
• Workarounds using convertShardKeyToHashed introduce compatibility risks, limited hash size (64-bit), and type conversion issues (e.g., can’t easily convert Long to hex string/ObjectId).
• Customer is open to discussing use cases in more depth.