Entity Pattern

In the Software Engineering community the term Entity can refer to many different things. In the context of es-entity it is generally meant in the sense put forward by Domain Driven Design. Strict adherence to DDD is not mandatory to use es-entity but there are a lot of benefits to be had by following these principles.

In DDD entities serve the following purpose:

• execute commands that
  • execute business logic
  • enforce domain invariants
  • mutate state
  • record events (in the context of Event Sourcing)
• supply queries that expose some of the entities state

They often host the most critical code in your application where correctness is of upmost importance. Ideally they are unit-testable and thus should not be overly coupled to the persistence layer (as they generally are when using just about any ORM library / framework). The design of es-entity is very deliberate in not getting in the way of testability of your Entities.

Each Entity type used in es-entity must have:

• an EntityId type
• an EntityEvent type
• a NewEntity type
• the Entity type itself