using interfaces/abstract classes with Entity Framework CodeFirst

Question

I have an Entity Framework CodeFirst Class (POCO) :

class Contract : IMyContract
{
   ...
}

interface IMyContract
{
   public int DateSigned{get;}
}

why am I not able to intercept context change operations in this way when a Contract is being modified by a client :

void context_SavingChanges(object sender, EventArgs e)
{

    foreach (ObjectStateEntry entry in
        ((ObjectContext)sender).ObjectStateManager.GetObjectStateEntries(
        EntityState.Added | EntityState.Modified | EntityState.Deleted))
    {

        IMyContract myContract = entry.Entity as IMyContract;
        if(myContract != null) 
        { 
           ...
        }
    }
}

Ladislav Mrnka · Accepted Answer · 2011-04-04 06:02:00Z

3

You mentioned Code-first but in the same time you are handling event of ObjectContext and casting sender to ObjectContext

Try this instead:

public class MyContext : DbContext
{
    private static EntityState[] states = new EntityState[] 
        { 
             EntityState.Added,
             EntityState.Modified,
             EntityState.Deleted,
        };

    ...

    public override int SaveChanges()
    {
        // If Entires<IMyContract> doesn't work use Entries() and check type 
        // inside the loop
        foreach(var entry in ChangeTracker.Entries<IMyContract>()
                                          .Where(e => states.Contains(e.State))
        {
           ...
        }
    }
}

answered Apr 4, 2011 at 6:02

Ladislav Mrnka

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4 Comments

Attilah Over a year ago

I'm using this to get to the Context object : var context = ((IObjectContextAdapter)database).ObjectContext; context.SavingChanges += new EventHandler(context_SavingChanges);

Attilah Over a year ago

the problem lies not with ObjectContext but with the fact that this never evaluates to true : DiscountEntity discountEntity = entry.Entity as DiscountEntity;

Ladislav Mrnka Over a year ago

And if you debug your application what type of the entity do you see in watch window?

Attilah Over a year ago

I can't get the WCF Data Service to run in debug mode and to hit breakpoints. really weird. I thought this (WCF Data Service) was the easiest way to expose data.

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