What is the difference between DAO and Repository patterns?

hibernate domain-driven-design ejb-3.0 repository-pattern data-access-layer
Thurein picture Thurein · Dec 18, 2011 · Viewed 171.2k times · Source

What is the difference between Data Access Objects (DAO) and Repository patterns? I am developing an application using Enterprise Java Beans (EJB3), Hibernate ORM as infrastructure, and Domain-Driven Design (DDD) and Test-Driven Development (TDD) as design techniques.

Answer

quentin-starin picture quentin-starin · Dec 18, 2011

DAO is an abstraction of data persistence.
Repository is an abstraction of a collection of objects.

DAO would be considered closer to the database, often table-centric.
Repository would be considered closer to the Domain, dealing only in Aggregate Roots.

Repository could be implemented using DAO's, but you wouldn't do the opposite.

Also, a Repository is generally a narrower interface. It should be simply a collection of objects, with a Get(id), Find(ISpecification), Add(Entity).

A method like Update is appropriate on a DAO, but not a Repository - when using a Repository, changes to entities would usually be tracked by separate UnitOfWork.

It does seem common to see implementations called a Repository that is really more of a DAO, and hence I think there is some confusion about the difference between them.

Related questions

DTO to Entity And Entity to DTO

We're to use DTO's to send data to and from the presentation layer. We have layers like: facade appService domain And We have use Dozer to help us convert entity to dto. But i have 2 question now: from entity to …

Read More
What are the possible values of the Hibernate hbm2ddl.auto configuration and what do they do

I really want to know more about the update, export and the values that could be given to hibernate.hbm2ddl.auto I need to know when to use the update and when not? And what is the alternative? These …

Read More
How to fix the Hibernate "object references an unsaved transient instance - save the transient instance before flushing" error

I receive following error when I save the object using Hibernate object references an unsaved transient instance - save the transient instance before flushing

Read More