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: , // 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).