How does the Repository Pattern Differ from a Simple Data Access Layer?

Question

I\'ve been confused by what I\'ve been reading during my research on the repository pattern. I\'m wondering if folks are (incorrectly?) using that word when they simply mean a d

Answer 1

Take a look at the "Using the IQueryable interface" section and beyond at Extending and Enhancing the Orders and Registrations Bounded Context. It provides an insightful and balanced discussion of DAO/Repository implementations.

As subsequently highlighted by Bob Horn, the Persistence Patterns articles summarises that:

Basically, the Repository pattern just means putting a façade over your persistence system so that you can shield the rest of your application code from having to know how persistence works.

Answer 2

In general I agree with author's statements, but I'd like to add some details

Difference between Repository and DAL/ORM that first not only abstracts the persistence mechanism, but also provides collection-like interface for accessing domain objects … and isolates domain objects from details of the database access code:

Differences

For external layers, such as Business Logic:

• Helps to avoid leaky abstraction. External layers depend on abstraction of Repository, rather than a specific implementation of DAL/ORM. Thus you could avoid all infrastructure and logical dependencies while working with Repository.
• operates with domain objects, rather then a instances of POJO/POCO/DTO
• CRUD operations applied to collection-like interface provided by Repository, rather then specific DAL/ORM methods. For example .net: working with collection that implements IEnumerable, rather then entity-framework context or nhibernate session

Similarities

Repository contains DAL/ORM underneath and serves same purpose