Question

I’m using Table per Hierarchy (TPH).
For example we have a base class for all entities:

public abstract class Entity
    {
        public virtual int Id { get; set; }

        public virtual bool IsTransient()
        {
            return Id == default(int);
        }
    }

And base class for several entitites:

public abstract class Event:Entity
    {
        [MaxLength(50)]
        [Required]
        public string Name { get; set; }

        [Required]
        public string Description { get; set; }

        [Required]
        [MaxLength(100)]
        public string ShortDescription { get; set; }

        [Required]
        public DateTime PublishDate { get; set; }

        public int  Duration { get; set; }
    }

public class Film:Event
    {
        public string Director { get; set; }

        public string ActorList { get; set; }

        public override string ToString()
        {
            return Name;
        }
    }

public class Concert:Event
    {
        public string Genre { get; set; }

        public override string ToString()
        {
            return Name;
        }
    }

My context:

public class MyContext:DbContext
    {
        public MyContext():base(ConfigurationManager.ConnectionStrings["MyContext"].ConnectionString)
        {
        }

        public DbSet<Event> Events { get; set; }

        public virtual void Commit()
        {
            base.SaveChanges();
        }

    }

This is base repository:

public class GenericRepository : IRepository
{
  //...   

    public IEnumerable<TEntity> GetAll<TEntity>() where TEntity : class
            {
                return GetQuery<TEntity>().AsEnumerable();
            } 

    public IQueryable<TEntity> GetQuery<TEntity>() where TEntity : class
            {          
                var entityName = GetEntityName<TEntity>();
                return ((IObjectContextAdapter)DbContext).ObjectContext.CreateQuery<TEntity>(entityName);
            }

private string GetEntityName<TEntity>() where TEntity : class
        {
            string entitySetName = ((IObjectContextAdapter)DbContext).ObjectContext
                 .MetadataWorkspace
                 .GetEntityContainer(((IObjectContextAdapter)DbContext).ObjectContext.DefaultContainerName, DataSpace.CSpace)  
                 .BaseEntitySets.First(bes => bes.ElementType.Name == typeof(TEntity).Name).Name;

            return string.Format("{0}.{1}", ((IObjectContextAdapter)DbContext).ObjectContext.DefaultContainerName, entitySetName);
        }

    }

Next, create context and repository:

var context = new MyContext();
EventRepository repository = new EventRepository(context);
var films = repository.GetAll<Film>();

But I get exception (in the GetEntityName method): the sequence does not have elements.
I think it because there are no Film table in the DB. How to solve this problem?

Answer 1

I don’t see the need of GetEntityName in the repository you are showing. For GetQuery you can use the DbContext API directly and don’t need to access the underlying ObjectContext or MetadataWorkspace:

public IQueryable<TEntity> GetQuery<TEntity>() where TEntity : class
{          
    return DbContext.Set<TEntity>();
}

This returns a DbSet<TEntity> (which is an IQueryable<TEntity>). I am not 100% sure if that also works if TEntity is derived but the MSDN documentation about DbSet<TEntity> says: “The type can be derived type as well as base type.” So, I would hope that the Set<TEntity>() method is allowed for derived types as well.