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Implementing the Repository Pattern

Implementing the Repository Pattern. Mike Hadlow Mikehadlow@yahoo.com http://mikehadlow.blogspot.com. Data Access Taxonomy. Record Set / Data Set Record Set / Data Set + Business Object Active Record Business Object + Data Access Object Domain Model + ??. Repository. Aggregate.

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Implementing the Repository Pattern

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  1. Implementing the Repository Pattern Mike Hadlow Mikehadlow@yahoo.com http://mikehadlow.blogspot.com

  2. Data Access Taxonomy • Record Set / Data Set • Record Set / Data Set + Business Object • Active Record • Business Object + Data Access Object • Domain Model + ??

  3. Repository

  4. Aggregate

  5. Repository • Encapsulate data access • Simple collection like interface • Should only return aggregate roots • Provide for adding and removing entities • Provide methods to select objects based on some criteria • Allow easy substitution

  6. QueryMethods Customer[] WithSurname(string surname)

  7. Specification Customer[] Find(ICustomerSpecification spec) boolICustomerSpecification.IsSatisfiedBy(Customer c) • Part of the Domain Model • Composable • Can define in-memory predicates and query predicates (SQL?) • Should we surface tool specific queries?

  8. Generic Repository IRepository<T> T[] Find<T>(ISpecification<T> specification)

  9. Rhino Commons

  10. Sharp Architecture

  11. Fluent NHibernate

  12. Is it a repository? • Does it show intent? • ICanDelete? ICanInsert? ICanUpdate? • Is polymorphism useful here? • But it’s ‘out there’!

  13. IQueryable? IQueryable<T> GetAll<T>() var customers = repository.GetAll().ThatMatch(criteria) .AsPagedList(pageNumber, pageSize); • SQL execution outside repository boundary • Query logic can seep into non-domain parts of the application

  14. Should Repositories control transactions? • Transactions should not be controlled by the repository. • Unit of Work (Nhibernate session, L2S DataContext) should not be controlled by the repository.

  15. Who consumes Repositories? • Views? • Controllers? • Domain Services? • Domain Entities?

  16. Questions? Mike Hadlow mikehadlow@yahoo.com http://mikehadlow.blogspot.com

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