How to get ObjectSet<T>'s entity key name?

Question

I've created a generic ObjectSet<T> in my generic repository.

What I would like to get is the name of the EntityKey of ObjectSet<T> so that I can use it in the DataContext.GetObjectByKey.

I've searched around and dug deep, but I can't seem to find this value anywhere in the ObjectSet class.

Answer 1

I looked a while ago for a nice way to do this and failed to find one. I generally end up building a GetEntityByKey extension method somewhere and within that, contatenating strings to build Entity Keys for TryGetObjectByKey calls. The general idea for building the entity key goes something like this:

internal class Program
{
    private static void Main(string[] args)
    {
        var dc = new AdventureWorksLT2008Entities();
        object c;
        dc.TryGetObjectByKey(GetEntityKey(dc.Customers, 23), out c);
        var customer = c as Customer;
        Console.WriteLine(customer.EmailAddress);
    }

    private static EntityKey GetEntityKey<T>(ObjectSet<T> objectSet, object keyValue) where T : class
    {
        var entitySetName = objectSet.Context.DefaultContainerName + "." + objectSet.EntitySet.Name;
        var keyPropertyName = objectSet.EntitySet.ElementType.KeyMembers[0].ToString();
        var entityKey = new EntityKey(entitySetName, new[] {new EntityKeyMember(keyPropertyName, keyValue)});
        return entityKey;
    }
}

You may be able to do something similar. This example assumes a single field per EntityKey for simplicity - for multiple value keys you would need to do something slightly more sophisticated with ObjectSet<T>.ElementType.KeyMembers and pass all your keys into the EntityKey constructor.

Answer 2

Generic:

public class GenericoRepositorio<T> : IGenericoRepositorio<T> where T : class
{
    protected readonly ObjectSet<T> ObjetoSet;
    protected readonly ModeloContainer Contexto;

    public GenericoRepositorio(ModeloContainer contexto)
    {
        Contexto = contexto;
        ObjetoSet = Contexto.CreateObjectSet<T>();
    }

    public T Carregar(int id)
    {
        object objeto;
        Contexto.TryGetObjectByKey(GetEntityKey(ObjetoSet, id), out objeto);
        return (T)objeto;
    }

    private static EntityKey GetEntityKey<T>(ObjectSet<T> objectSet, object keyValue) where T : class
    {
        var entitySetName = objectSet.Context.DefaultContainerName + "." + objectSet.EntitySet.Name;
        var keyPropertyName = objectSet.EntitySet.ElementType.KeyMembers[0].ToString();
        var entityKey = new EntityKey(entitySetName, new[] { new EntityKeyMember(keyPropertyName, keyValue) });
        return entityKey;
    }
}