Entity Framework 4.1 Generic Repository set up

Question

I\'m new to Entity Framework and joined a project that uses a generic repository as shown below. Are there any disadvantages to the way the repository is set up? I\'ve notic

Answer 1

The main disadvantage of using a generic repository instead of having a concrete repository implementation per Aggregate root, is that you cannot create specific methods for specific usages.

Having all your repositories inherit from a base repository let you create methods like: GetProductsInsSock() or things like UpdateOnlyProductsThatSatisfySomething().

But some workarounds are available! ;-)

Keep on using your generic repository if it suits to your team, the only thing you might have to add is a method that accept a Specification as parameter. As Eric Evans and Martin Fowler say:

The central idea of Specification is to separate the statement of how to match a candidate, from the candidate object that it is matched against.

In your case it could work as a filter to retrieve the right entities without having the need to create a specific method.

You could simply add this to your IRepository interface:

IEnumerable<T> Find(Specification<T> predicate);

The method implementation in your Repository class would be like this:

public class Repository<T> : IRepository<T> where T : class
{
  public Repository(IDbContext context)
  {
    _context = context;
    _dbset   = context.Set<T>();
  }

  // some code...

  public IEnumerable<T> Find(Specification<T> specification)
  {
    return _dbset.Where(specification.Predicate);
  }

  // some code...
}

The Specification class could look like this:

public class Specification<T>
{
  public Specification(Expression<System.Func<T, bool>> predicate)
  {
    _predicate = predicate;
  }

  internal Expression<System.Func<T, bool>> Predicate
  {
    get { return _predicate; }
  }

  private readonly Expression<System.Func<T, bool>> _predicate;
}

A call example:

var specification = ProductSpecification.InStock();
var product = Repository.Find(specification).FirstOrDefault();

And finally, the ProductSpecification class:

internal static class ActionSpecification
{
  internal static Specification<Product> InStock()
  {
    return new Specification<Product>(p => p.IsInStock == true);
  }
}