How to handle updating entities. NHibernate + ASP.NET MVC

Question

I cannot update created previously entity. I'm getting a StaleObjectException exception with message:

Row was updated or deleted by another transaction (or unsaved-value mapping was incorrect): [Project.DomainLayer.Entities.Employee#00000000-0000-0000-0000-000000000000]

I don't share the update process with anyone. What's the problem?

Data Access / DI

public class DataAccessModule : Ninject.Modules.NinjectModule
{
    public override void Load()
    {
        this.Bind<ISessionFactory>()
            .ToMethod(c => new Configuration().Configure().BuildSessionFactory())
            .InSingletonScope();

        this.Bind<ISession>()
            .ToMethod(ctx => ctx.Kernel.TryGet<ISessionFactory>().OpenSession())
            .InRequestScope();

        this.Bind(typeof(IRepository<>)).To(typeof(Repository<>))
            .InRequestScope();
    }
}

Data Access / Mappings

<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="Project.DomainLayer"   namespace="Project.DomainLayer.Entities">
<class name="Employee" optimistic-lock="version">
    <id name="ID" column="EmployeeID" unsaved-value="00000000-0000-0000-0000-000000000000">
        <generator class="guid.comb" />
    </id>
    <version name="Version" type="Int32" column="Version" />
    <!-- properties -->
    <property name="EmployeeNumber" />
    <!-- ... -->
    <property name="PassportRegistredOn" not-null="true" />
    <!-- sets -->
    <set name="AttachedInformation" cascade="all">
        <key column="EmployeeID" />
        <element column="Attachment" />
    </set>
    <set name="TravelVouchers" cascade="all">
        <key column="EmployeeID" />
        <one-to-many class="TravelVoucher" />
    </set>
  </class>
</hibernate-mapping>

Data Access / Repository

public class Repository<T> : IRepository<T> where T : AbstractEntity<T>, IAggregateRoot
{
    private ISession session;

    public Repository(ISession session)
    {
        this.session = session;
    }

    // other methods are omitted

    public void Update(T entity)
    {            
        using(var transaction = this.session.BeginTransaction())
        {
            this.session.Update(entity);
            transaction.Commit();
        }
    }
    public void Update(Guid id)
    {            
        using(var transaction = this.session.BeginTransaction())
        {
            this.session.Update(this.session.Load<T>(id));
            transaction.Commit();
        }
    }
} 

Inside a Controller

public class EmployeeController : Controller
{
    private IRepository<Employee> repository;

    public EmployeeController(IRepository<Employee> repository)
    {
        this.repository = repository;
    }        
    public ActionResult Edit(Guid id)
    {
        var e = repository.Load(id);
        return View(e);
    }
    [AcceptVerbs(HttpVerbs.Post)]
    public ActionResult Edit(Employee employee)
    {
        if(ModelState.IsValid)
        {
            repository.Update(employee);
            return RedirectToAction("Deatils", "Employee", new { id = employee.ID });
        }
        else
        {
            return View(employee);
        }
    }
}

How do I update my entities? Thanks!

EDIT

So I added unsaved-value="{Guid.Empty goes here}" to my markup. Moreover I've tried to do the next thing:

public void Update(T entity)
{
    using(var transaction = this.session.BeginTransaction())
    {
        try
        {
            this.session.Update(entity);
            transaction.Commit();
        }
        catch(StaleObjectStateException ex)
        {
            try
            {
                session.Merge(entity);
                transaction.Commit();
            }
            catch
            {
                transaction.Rollback();
                throw;
            }
        }

    }
}

And this gives me the same effect.. I mean transaction.Commit(); after Merge gives the same exception.

Also I'm wondering should I expose, using hidden input, the entity ID on the Edit view?

EDIT

So entity really detaches. When it passes to controller the ID equals Guid.Empty. How do I handle it, Merge or Reattach?

Answer 1

There are two scenarios that you can run into, given your code pattern.

1. You could retrieve the object from the db using ISession.Get() which can be followed by a change/update to the retrieved object. For this change to be effective, all you need to do is flush the session or commit the transaction as Nhibernate will track all the changes for you automatically.

2. You have a transient instance, an object that is not associated with the ISession in context, from which you want to update. In this case, from my experience, the best practice is to ISession.Get() the object and make the corresponding changes to the object you just retrieve. (usually your view model is different from your domain model as well, don't mix both) This pattern is shown below. It works all the time. Make sure you also use ISession.SaveOrUpdate().

[AcceptVerbs(HttpVerbs.Post)]
public ActionResult Edit(Employee employee)
{
    if(ModelState.IsValid)
    {
        var persistentEmployee = repository.Get(employee.Id);
        if(  persistentEmployee == null){
            throw new Exception(String.Format("Employee with Id: {0} does not exist.", employee.Id));
        }
        persistentEmployee.Name = employee.Name;
        persistentEmployee.PhoneNumber = employee.PhoneNumber;
        //and so on
        repository.Update(persistentEmployee);
        return RedirectToAction("Deatils", "Employee", new { id = employee.ID });
    }
    else
    {
        return View(employee);
    }
}

Also, notice that your controller is probably instantiated on a per-request basis, hence, the lifetime of your ISession does not span multiple calls to the different methods you have in your controller. In other words, every method is almost always working within the context of a new ISession (unit of work).

Answer 2

Your logic is not good, becouse you use domain model like Employee as ViewModel. Best practice is use CreateEmploeeViewModel and EditEmployeeViewModel and separate Domain Logic and View Model logic. For Example:

public class Employee 
 {
        public virtual int Id { get; set; }

        public virtual string FirstName { get; set; }

        public virtual string LastName { get; set; }

        public virtual string MiddleName { get; set; }
 }

public class CreateEmployeeViewModel 
 {
        public virtual string FirstName { get; set; }

        public virtual string LastName { get; set; }

        public virtual string MiddleName { get; set; }
 }

public class EditEmployeeViewModel : CreateEmployeeViewModel  
 {
        public virtual int Id { get; set; }
 }

To convert from Employee to ViewModel I prefer yo use Automapper.

So controller Actions become to looks like:

[HttpGet]
    public virtual ActionResult Edit(int id)
    {
        Employee entity = GetEntityById(id);
        EmployeeEditViewModel model = new EmployeeEditViewModel();

        Mapper.Map(source, destination);            

        return View("Edit", model);
    }

    [HttpPost]
    public virtual ActionResult Edit(EmployeeEditViewModel model)
    { 
        if (ModelState.IsValid)
        {
            Employee entity = GetEntityById(model.Id);

            entity = Mapper.Map(model, entity);               
            EntitiesRepository.Save(entity);

            return GetIndexViewActionFromEdit(model);
        }           

        return View("Edit", model);
    }

In this case NHibernate knows that you update Employee, and you can`t remove some properties which not exist in your View.