In the database world, it is frequently important to have unique identifiers associated with a record. In a legacy, tabular database, these unique identifiers are often used as primary keys. In a modern database, such as MongoDB, we need a unique identifier in an `_id` field as a primary key as well. MongoDB provides an automatic unique identifier for the `_id` field in the form of an `ObjectId` data type.
For those that are familiar with MongoDB Documents, you've likely come across the `ObjectId` data type in the `_id` field. For those unfamiliar with MongoDB Documents, the [ObjectId](https://alger.me/mongodb-objectid) datatype is automatically generated as a unique document identifier if no other identifier is provided. But what is an `ObjectId` field? What makes them unique? This post will unveil some of the magic behind the BSON ObjectId data type. First, though, what is BSON?