Speaking of database access Domain-Driven Design defines repositories that will manage persistence and consistency of entities. The motivation behind repositories was to have a single point of responsibility that enables the domain model to be persistent with consistency in mind. Defining these functionalities should not clutter the domain model code with persistence implementation details. Therefore, Domain-Driven Design defines the concept of repositories which encapsulate these operations in a self-sufficient and consistent way.

The repositories are the entry point for persistence operations for a specific entity type. Since only instances of aggregates and entities need to be identified, only these types require repositories.

In Java EE and JPA, there is already a functionality that matches the idea of repositories well, JPA's EntityManager. The entity manager is used to persist, retrieve, and manage objects that are defined as entities or potential object hierarchies thereof. The fact that the JPA managed objects need to be identifiable entities perfectly fits the constraints set by the Domain-Driven Design idea of entities.

The entity manager is injected and used in managed beans. This matches the idea that services, either as boundaries or controls, are meant to orchestrate the business use case, here by invoking the entity manager to provide the persistence of the entities.