Question

I’m trying to implement the Repository/Unit-of-Work pattern for EF5 on .NET 4.5 as described here: http://www.asp.net/mvc/tutorials/getting-started-with-ef-using-mvc/implementing-the-repository-and-unit-of-work-patterns-in-an-asp-net-mvc-application. This all works great until I try to use self-referencing entities as described here: http://www.codeproject.com/Articles/206410/How-to-Configure-a-Self-Referencing-Entity-in-Code. When I try to do anything (get a specify entity, get all entities, add an entity, etc.) with the repository that contains the self referencing entity (FieldType) I get a stackoverflowexception on the getter of the FieldTypeRepository in my UnitOfWork class. Don’t worry, the irony of posting a stackoverflowexception on stackoverflow isn’t lost on me. I’ve read quite a few SO articles about the repository pattern for EF but haven’t seen anything combining them with self-referencing entities.

Things I’ve tried:

• Using FluentAPI instead of attributes on the FieldType entity – no change
• Using the Context object directly – this works perfectly, entities are added to the DB and reference each other properly, unfortunately that defeats the purpose of the repository pattern
• Using the repository for non-self referencing entities – works great
• Using EF5 for .NET 4.0 and .NET 4.5 – same results

My code:

FieldType.cs

public class FieldType
{
    [Key]
    [DatabaseGeneratedAttribute(System.ComponentModel.DataAnnotations.Schema.DatabaseGeneratedOption.Identity)]
    public int FieldTypeId { get; private set; }

    public string Name { get; set; }

    public string Description { get; set; }

    public int? ParentFieldTypeId { get; set; }

    [ForeignKey("ParentFieldTypeId")]
    public virtual FieldType ParentFieldType { get; set; }
}

UnitOfWork.cs

public class UnitOfWork : IDisposable
{
    private Context context = new Context();

    private Repository<FieldType> fieldTypeRepository;

    public Repository<FieldType> FieldTypeRepository
    {
        // EXCEPTION OCCURS HERE
        get
        {
            if (this.fieldTypeRepository == null)
            {
                this.fieldTypeRepository = new Repository<FieldType>(this.context);
            }

            return this.FieldTypeRepository;
        }
    }

    public void Save()
    {
        this.context.SaveChanges();
    }
}

Context.cs

public class Context : DbContext
{
    public Context()
        : base("echo")
    {
    }

    public DbSet<FieldType> FieldTypes { get; set; }
}

Repository.cs

public class Repository<TEntity> where TEntity : class
{
    private Context context;

    private DbSet<TEntity> dbSet;

    public Repository(Context context)
    {
        this.context = context;
        this.dbSet = context.Set<TEntity>();
    }

    public virtual IEnumerable<TEntity> Get(
        Expression<Func<TEntity, bool>> filter = null,
        Func<IQueryable<TEntity>, IOrderedQueryable<TEntity>> orderBy = null,
        string includedProperties = "")
    {
        IQueryable<TEntity> query = this.dbSet;

        if (filter != null)
        {
            query = query.Where(filter);
        }

        foreach (var includeProperty in includedProperties.Split(new char[] { ',' }, StringSplitOptions.RemoveEmptyEntries))
        {
            query = query.Include(includeProperty);
        }

        if (orderBy != null)
        {
            return orderBy(query).ToList();
        }
        else
        {
            return query.ToList();
        }
    }

    public virtual TEntity GetById(object id)
    {
        return this.dbSet.Find(id);
    }

    public virtual void Insert(TEntity entity)
    {
        this.dbSet.Add(entity);
    }

    public virtual void Delete(object id)
    {
        TEntity entityToDelete = this.dbSet.Find(id);
        this.Delete(entityToDelete);
    }

    public virtual void Delete(TEntity entityToDelete)
    {
        if (this.context.Entry(entityToDelete).State == EntityState.Detached)
        {
            this.dbSet.Attach(entityToDelete);
        }

        this.dbSet.Remove(entityToDelete);
    }

    public virtual void Update(TEntity entityToUpdate)
    {
        this.dbSet.Attach(entityToUpdate);
        this.context.Entry(entityToUpdate).State = EntityState.Modified;
    }
}

SecurityController.cs (or any class really)

public class SecurityController : Controller
{
    public ActionResult Login()
    {
        using (UnitOfWork unitOfWork = new UnitOfWork())
        {
            var fieldType = unitOfWork.FieldTypeRepository.GetById(1);
            //THIS COULD BE ANY TYPE OPERATION
        }

        return this.View();
    }

Answer 1

Thanks Gert, for helping me realize that it’s not a problem with EF or self-referencing types but rather that I was calling the get method for the FieldTypeRepository from itself… http://www.youtube.com/watch?v=g6GuEswXOXo