ObjectId

Small, likely unique, fast to generate, ordered identifier.

• Small: Each ObjectId is 12 bytes long, shorter than a UUID's 16 bytes.

• Likely unique: Each driver randomly selects a generation range, so conflicts are unlikely.

• Fast to generate: Depending on the generation strategy, generating a new ObjectId may be as simple as querying the time and incrementing a counter.

• Ordered: All ObjectId instances can be sorted by creating date, with a precision of one second. Two ObjectId instances created by the same driver are sorted with even more precision.

Composition

An ObjectId is composed of:

• A 4-byte timestamp, representing the ObjectId's creation date, with a precision of one second,

• A 5-byte random processId, unique to each machine and process, to decrease conflicts,

• A 3-byte incrementing counter, initialized at a random value.

ObjectId instances are generally represented as 24-characters hexadecimal strings:

ObjectId("699dfad90ca573f85c0eec1c").hex // 699dfad90ca573f85c0eec1c

Generating new ObjectIds

There are different strategies to generate new ObjectId instances; they are encoded by the ObjectIdGenerator interface.

The ObjectIdGenerator used by each driver is available directly on each collection:

users.insert(
    User(
        _id = users.newId(), // Generate an ObjectId using the configuration specific to that collection
        name = "Bob",
    )
)

External resources

• Official documentation

Thread safety

Instances of this class are immutable and thread-safe.