What is the last type in MongoDB's sort comparison order?

In MongoDB, the sort comparison order is defined by a specific hierarchy of types, determining how different data types are compared when sorting documents. The internal type MaxKey is the highest type in this hierarchy, meaning that when sorting, any value of MaxKey will be considered greater than any other value of any other type.

This designation as the last type in the sort comparison order allows MongoDB to effectively handle comparisons when sorting documents with mixed data types. MaxKey is designed primarily for internal use, such as when ensuring that a query returns all documents regardless of other types present in the collection. Understanding this hierarchy is crucial for developers to predict how results will be sorted when using the sort operation with various data types, including ObjectId, Boolean, and Date.

In contrast, the other options (ObjectId, Boolean, and Date) fall lower in the comparison order and are not considered the last type. This means that when they are sorted against MaxKey, they will always rank lower, making MaxKey uniquely significant in the sorting mechanism of MongoDB.