Aggregates carry out many important functions. One of them is maintaining consistency boundaries. In this post, I write about the requirement of global email uniqueness and how it is related to aggregate invariants.

While such classes as Person and Money are pretty intuitive and can be easily attributed to either entities or value objects, the choice isn’t so obvious when it comes to classes that are internal to an aggregate. That is classes that aren’t roots of their own aggregates but rather parts of existing ones.