entity framework programming against interface and repository pattern

Question

I am developing in ASP.NET MVC3 and EntityFramework.

I want my model to follow an interface :

public class Account : IAccount
{
    public string Id { get; set; }

    public DateTime Date { get; set; }

    public string Language { get; set; }
}

public interface IAccount
{
    string Id { get; set; }

    DateTime Date { get; set; }

    string Language { get; set; }
}

Here's my Context

public class EFContext : DbContext, IContext
{
    public DbSet<Account> Accounts { get; set; }
}

And here's the repository :

public interface IRepository<T> where T : class
{
    IQueryable<T> All { get; }
    int Count { get; }

    bool Contains(Expression<Func<T, bool>> predicate);

    void Create(T item);

    void Update(T item);

    void Delete(Expression<Func<T, bool>> predicate);
    void Delete(T item);
}

public class EFRepository<T> : IRepository<T> where T : class
{
    private EFContext _context;

    public EFRepository(IUnitOfWork uow)
    {
        this._context = (EFContext)uow.Context;
    }

    protected DbSet<T> DbSet
    {
        get
        {
            return _context.Set<T>();
        }
    }

    public IQueryable<T> All
    {
        get
        {
            return DbSet.AsQueryable();
        }
    }

    public virtual int Count
    {
        get
        {
            return DbSet.Count();
        }
    }

    public bool Contains(Expression<Func<T, bool>> predicate)
    {
        return DbSet.Count(predicate) > 0;
    }

    public virtual void Create(T item)
    {
        DbSet.Add(item);
    }

    public virtual void Update(T TObject)
    {
        var item = DbSet.Attach(TObject);

        _context.SetItemState(TObject, EntityState.Modified);
    }

    public virtual void Delete(Expression<Func<T, bool>> predicate)
    {
        var objects = DbSet.Where(predicate);

        foreach (var obj in objects)
        {
            DbSet.Remove(obj);
        }
    }

    public virtual void Delete(T TObject)
    {
        DbSet.Remove(TObject);
    }
}

Now, I want to use IRepository<IAccount> but this will ask the context for DbSet<IAccount>. This leads to an error since the Context contains a DbSet<Account>.

I then tried the solution proposed here for Linq2Sql : http://iridescence.no/post/Linq-to-Sql-Programming-Against-an-Interface-and-the-Repository-Pattern.aspx

So I added this function to my EFContext

public new DbSet<T> Set<T>() where T : class
{
    var ciccio = TableMaps[typeof(T)];
    return (DbSet<T>)base.Set(ciccio).Cast<T>();
}

But it doesn't work.

Do anyone have a suggestion? Thx

"It doesn't work" is not an intelligent way to debug a problem. What is the error message? — usr
– usr, Commented Mar 31, 2012 at 16:01
@Slauma, an interface is not incompatible with T when a where T : class is present. — smartcaveman
– smartcaveman, Commented Nov 15, 2012 at 15:38
@smartcaveman: True, I even didn't know that until now. Deleted my comment which was obvious nonsense then. Thanks! — Slauma
– Slauma, Commented Nov 15, 2012 at 15:55

Erik Funkenbusch · Accepted Answer · 2012-03-31 16:37:00Z

3

What benefit are you receiving from using an interface for your entities? I don't see any value here. Typically, you use Interfaces to remove dependencies upon the implementation, but that's not what you're achieving here because you're returning a concrete DbSet of objects.

Your entities are already Poco's. They don't have dependencies on other implemntations, and they have no code in them other than a getter/setter. Using an interface is redundant and pointless.

answered Mar 31, 2012 at 16:37

Erik Funkenbusch

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8 Comments

user1012750 Over a year ago

I am using interfaces because I need to switch between EF and Linq2Sql. In this way the controllers use the interface and EF and Linq2Sql can implement their own classes for the model

Erik Funkenbusch Over a year ago

@user1012750 - You can use a common Poco model for both, without interfaces. For how to do poco in L2S see the answer to this question stackoverflow.com/questions/1407342/…

Erik Funkenbusch Over a year ago

@user1012750 - this is a textbook example of the XY problem. meta.stackexchange.com/questions/66377/what-is-the-xy-problem - Instead of asking how to share a common model between L2S and EF, you instead come up with a silly solution that you can't make work, and then ask how to make your silly solution work.

user1012750 Over a year ago

Well, first of all I didn't ask how to make my silly solution work... I just asked for suggestions. So, thanks for the suggestion, but I dont see how to share a common model between the two techs.

Erik Funkenbusch Over a year ago

@user1012750 - Hey, no sweat off my back. I gave you a solution to your real problem and you choose to ignore it and get huffy. Getting mad at people trying to help you does not do you any good, it just alienates those that try to help you.

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user1012750 · Accepted Answer · 2012-04-01 12:36:24Z

-1

I've found a workaround. I kind of like it so I want to share it.

I rewritten my EFRepository :

public class EFRepository<T, W> : 
IRepository<T> where T : class
    where W : class, T
{
    private EFContext _context;

    public EFRepository(IUnitOfWork uow)
    {
        this._context = (EFContext)uow.Context;
    }

    protected DbSet<W> DbSet
    {
        get
        {                
            return _context.Set<W>();
        }
    }

    public IQueryable<T> All
    {
        get
        {
            return DbSet.AsQueryable<T>();
        }
    }

    public virtual int Count
    {
        get
        {
            return DbSet.Count();
        }
    }

    public bool Contains(Expression<Func<T, bool>> predicate)
    {
        return All.Count(predicate) > 0;
    }

    public virtual void Create(T item)
    {
        DbSet.Add(item as W);
    }

    public virtual void Update(T TObject)
    {
        var item = DbSet.Attach(TObject as W);

        _context.SetItemState(TObject, EntityState.Modified);
    }

    public virtual void Delete(Expression<Func<T, bool>> predicate)
    {
        var objects = All.Where(predicate);

        foreach (var obj in objects)
        {
            DbSet.Remove(obj as W);
        }
    }

    public virtual void Delete(T TObject)
    {
        DbSet.Remove(TObject as W);
    }
}

So now basically all I need to do now is

IRepository<IAccount>> accRepository = new EFRepository<IAccount, Account>(uow);

I am happy with this solution, but still I'm not sure it is the best one, so any comments will be appreciated.

Thanks

answered Apr 1, 2012 at 12:36

user1012750

13312 bronze badges

6 Comments

Erik Funkenbusch Over a year ago

How exactly do you intend to do navigational properties? These work different between L2S and EF. For instance, EF supports many-to-many while L2S does not.

user1012750 Over a year ago

Well, databases do not support many-to-many relationship, so I will just pass by the intermediate table. See here : iaingalloway.com/many-to-many-relationships-in-linq-to-sql

Erik Funkenbusch Over a year ago

If you're going to degrade the performance and functionality of EF to match L2S, why even bother with EF?

user1012750 Over a year ago

I am working with ef but my host provider has problem with it. So i switch between ef and l2s.

Erik Funkenbusch Over a year ago

That's not possible. EF is an entirely client-side tool, your hosting provider has nothing to do with it. He can't support or not support EF so long as he supports .NET

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