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Asked: 2026-06-10T13:27:18+00:00

I am creating a service for which I will use MongoDB as a storage

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I am creating a service for which I will use MongoDB as a storage backend.
The service will produce a hash of the user input and then see if that same hash (+ input) already exists in our dataset.

The hash will be unique yet random ( = non-incremental/sequential), so my question is:

  1. Is it -legitimate- to use a random value for an Object ID? Example:

$object_id = new MongoId(HEX-OF-96BIT-HASH);

Or will MongoDB treat the ObjectID differently from other server-produced ones, since a “real” ObjectID also contains timestamps, machine_id, etc?

What are the pros and cons of using a ‘random’ value? I guess it would be statistically slower for the engine to update the index on inserts when the new _id’s are not in any way incremental – am I correct on that?

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  1. Editorial Team

    Yes it is perfectly fine to use a random value for an object id, if some value is present in _id field of a document being stored, it is treated as objectId.

    Since _id field is always indexed, and primary key, you need to make sure that different objectid is generated for each object.
    There are some guidelines to optimize user defined object ids :

    https://docs.mongodb.com/manual/core/document/#the-id-field.

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