Edit entity in Ef - UnitOfWork - asp.net-mvc

Question

I am using this template for my project
public interface IUnitOfWork
{
IDbSet<TEntity> Set<TEntity>() where TEntity : class;
int SaveChanges();
void RejectChanges();
DbEntityEntry<TEntity> Entry<TEntity>(TEntity entity) where TEntity : class;
}
Implementation:
public class BookStoreDbContext : DbContext, IUnitOfWork
{
public DbSet<Categori> Categoris { get; set; }
public new DbEntityEntry<TEntity> Entry<TEntity>(TEntity entity) where TEntity : class
{
return base.Entry(entity);
}
public override int SaveChanges()
{
return base.SaveChanges();
}
Controler:
public class CategoriController : Controller
{
private IUnitOfWork _uw;
private ICategoriService _categoriService;
public CategoriController(IUnitOfWork uw,ICategoriService categoriservice )
{
_uw = uw;
_categoriService = categoriservice;
}
public ActionResult Edit(int id = 0)
{
var categori = _categoriService.Find(i => i.Id == id);
if (categori == null)
{
return HttpNotFound();
}
return View(categori);
}
[HttpPost]
public ActionResult Edit(Categori categori)
{
if (ModelState.IsValid)
{
_uw.Entry(categori).State = EntityState.Modified;
_uw.SaveChanges();
}
return View(categori);
}
}
Repository or Servis layer:
public interface IGenericService<T> : IDisposable where T : class
{
void Add(T entity);
void Delete(T entity);
T Find(Func<T, bool> predicate);
IList<T> GetAll();
IList<T> GetAll(Func<T, bool> predicate);
}
public interface ICategoriService : IGenericService<DomainClasses.Models.Categori>
{
}
impliment repository:
public class EfGenericService<TEntity> : IGenericService<TEntity> where TEntity : class
{
protected IUnitOfWork _uow;
protected IDbSet<TEntity> _tEntities;
public EfGenericService(IUnitOfWork uow)
{
_uow = uow;
_tEntities = _uow.Set<TEntity>();
}
public virtual void Add(TEntity entity)
{
_tEntities.Add(entity);
}
public void Delete(TEntity entity)
{
_tEntities.Remove(entity);
}
public TEntity Find(Func<TEntity, bool> predicate)
{
return _tEntities.Where(predicate).FirstOrDefault();
}
public IList<TEntity> GetAll()
{
return _tEntities.ToList();
}
public IList<TEntity> GetAll(Func<TEntity, bool> predicate)
{
return _tEntities.Where(predicate).ToList();
}
public class EfCategoriService : EfGenericService<Categori>,ICategoriService
{
public EfCategoriService(IUnitOfWork uow)
: base(uow)
{
}
}
Global.asax
private static void InitStructureMap()
{
ObjectFactory.Initialize(
x =>
{
x.For<IUnitOfWork>().HttpContextScoped().Use(() => new BookStoreDbContext());
x.ForRequestedType<ServiceLayer.Interfaces.ICategoriService>()
.TheDefaultIsConcreteType<EfCategoriService>();
}
But I get this error when update entity:
Store update, insert, or delete statement affected an unexpected number of rows (0). Entities may have been modified or deleted since entities were loaded. Refresh ObjectStateManager entries
Please help me to resolve this error?

Answer 1

The only relevant lines in your snippets are:
_uw.Entry(categori).State = EntityState.Modified;
_uw.SaveChanges();
Now, look at the exception you get:
Store update, insert, or delete statement affected an unexpected
number of rows (0). Entities may have been modified or deleted since
entities were loaded.
Does setting the entity state to Modified insert an entity? No.
Does it delete an entity? No.
Does it update an entity? Yes.
May the entity that EF tries to update have been deleted? Well, perhaps. How to check that? When an entity is deleted the database must know the key in order to know which row to delete. To confirm if the key is correct use a debugger in your controller post action, inspect the key value of categori that is passed into the method. Does it have the expected value? If not, you probably have a problem in your view or with binding the form and route values to the categori model. If yes, check in the database if the entity with that key is in the database table. If yes, next point.
May the entity have been modified? It could happen that EF "thinks" it has been modified in the database (even if it hasn't) if you have marked another property in your Categori model as a concurrency token. If that property has changed in the database or in the view between loading the entity in the GET request and reattaching (setting the state to Modified) and SaveChanges in the POST request you'll get a concurrency violation.
Priority has the test in bold above because it is the most likely cause of the problem in my opinion. If it turns out that the key doesn't have the expected value better ask a new question because it will be a pure ASP.NET MVC question that has nothing to do with EF and your UOW and service architecture.