Automapper with NHibernate - How to persist mapped objects? - asp.net-mvc

Question

I have an ASP.NET MVC application that uses Fluent NHibernate and AutoMapper.
I am primarily using AutoMapper to map my Models to ViewModels and vice versa.
When doing the latter, mapping from my viewmodel back to a model, I am wondering how I can map this to a specific instance from the DB, so when I commit the changes back to the DB (using my NHibernate repository layer, via my service layer), the changes are persisted.
Example:
var advert = Mapper.Map<AdvertViewModel, Advert>(model);
_advertService.UpdateAdvert(advert); // then calls repo which commits current NHibernate trans * Nothing in the DB changes *
If I attempt to commit my NHibernate session, so as to UPDATE this advert in the DB, despite the advert being assigned the correct Key/Id as part of the mapping, I guess because the NHibernate session knows nothing about this advert instance(?) it doesn't write away the changes.
Therefore, I am wondering how to handle this mapping scenario in conjunction with NHibernate?

Answer 1

You could do the following:
// fetch the domain model to update
var domainModelToUpdate = _advertService.Get(viewModel.Id);
// Map the properties that are present in the view model to the domain model
// leaving other properties intact
Mapper.Map<AdvertViewModel, Advert>(viewModel, domainModelToUpdate);
// Update the domain model
_advertService.UpdateAdvert(domainModelToUpdate);
But if the view model already contains everything, you don't need to fetch the domain model before updating. All you have to do is to specify the unsaved-value on your identity column mapping to so that NHibernate knows whether an instance is transient or not and then use SaveOrUpdate:
Id(x => x.ID).WithUnsavedValue(0);
or if you are using nullable integers for your identities pass null.

Answer 2

If it is indeed a session issue - the following singleton might help you out
/// <summary>
/// Handles creation and management of sessions and transactions. It is a singleton because
/// building the initial session factory is very expensive. Inspiration for this class came
/// from Chapter 8 of Hibernate in Action by Bauer and King. Although it is a sealed singleton
/// you can use TypeMock (http://www.typemock.com) for more flexible testing.
/// </summary>
public sealed class NHibernateSessionManager
{
#region Thread-safe, lazy Singleton
System.IO.StreamWriter ConsoleWriter = null;
/// <summary>
/// This is a thread-safe, lazy singleton. See http://www.yoda.arachsys.com/csharp/singleton.html
/// for more details about its implementation.
/// </summary>
public static NHibernateSessionManager Instance
{
get
{
return Nested.NHibernateSessionManager;
}
}
/// <summary>
/// Initializes the NHibernate session factory upon instantiation.
/// </summary>
private NHibernateSessionManager()
{
InitSessionFactory();
}
/// <summary>
/// Assists with ensuring thread-safe, lazy singleton
/// </summary>
private class Nested
{
static Nested() { }
internal static readonly NHibernateSessionManager NHibernateSessionManager =
new NHibernateSessionManager();
}
#endregion
private void InitSessionFactory()
{
// Hold the config var
FluentConfiguration config = Fluently.Configure();
// Set the DB config
MsSqlConfiguration dbConfig = MsSqlConfiguration.MsSql2005.ConnectionString(ConfigurationManager.ConnectionStrings["iSearchConnection"].ConnectionString);
config.Database(dbConfig);
// Load mappings from this assembly
config.Mappings(m => m.FluentMappings.AddFromAssembly(Assembly.GetExecutingAssembly()));
// Create session factory
sessionFactory = config.BuildSessionFactory();
}
/// <summary>
/// Allows you to register an interceptor on a new session. This may not be called if there is already
/// an open session attached to the HttpContext. If you have an interceptor to be used, modify
/// the HttpModule to call this before calling BeginTransaction().
/// </summary>
public void RegisterInterceptor(IInterceptor interceptor)
{
ISession session = ContextSession;
if (session != null && session.IsOpen)
{
throw new CacheException("You cannot register an interceptor once a session has already been opened");
}
GetSession(interceptor);
}
public ISession GetSession()
{
return GetSession(null);
}
/// <summary>
/// Gets a session with or without an interceptor. This method is not called directly; instead,
/// it gets invoked from other public methods.
/// </summary>
private ISession GetSession(IInterceptor interceptor)
{
ISession session = ContextSession;
if (session == null)
{
if (interceptor != null)
{
session = sessionFactory.OpenSession(interceptor);
}
else
{
session = sessionFactory.OpenSession();
}
ContextSession = session;
}
return session;
}
/// <summary>
/// Flushes anything left in the session and closes the connection.
/// </summary>
public void CloseSession()
{
ISession session = ContextSession;
if (session != null && session.IsOpen)
{
session.Flush();
session.Close();
}
if (ConsoleWriter != null)
{
ConsoleWriter.Flush();
ConsoleWriter.Close();
}
ContextSession = null;
}
public void BeginTransaction()
{
ITransaction transaction = ContextTransaction;
if (transaction == null)
{
transaction = GetSession().BeginTransaction();
ContextTransaction = transaction;
}
}
public void CommitTransaction()
{
ITransaction transaction = ContextTransaction;
try
{
if (HasOpenTransaction())
{
transaction.Commit();
ContextTransaction = null;
}
}
catch (HibernateException)
{
RollbackTransaction();
throw;
}
}
public bool HasOpenTransaction()
{
ITransaction transaction = ContextTransaction;
return transaction != null && !transaction.WasCommitted && !transaction.WasRolledBack;
}
public void RollbackTransaction()
{
ITransaction transaction = ContextTransaction;
try
{
if (HasOpenTransaction())
{
transaction.Rollback();
}
ContextTransaction = null;
}
finally
{
CloseSession();
}
}
/// <summary>
/// If within a web context, this uses <see cref="HttpContext" /> instead of the WinForms
/// specific <see cref="CallContext" />. Discussion concerning this found at
/// http://forum.springframework.net/showthread.php?t=572.
/// </summary>
private ITransaction ContextTransaction
{
get
{
if (IsInWebContext())
{
return (ITransaction)HttpContext.Current.Items[TRANSACTION_KEY];
}
else
{
return (ITransaction)CallContext.GetData(TRANSACTION_KEY);
}
}
set
{
if (IsInWebContext())
{
HttpContext.Current.Items[TRANSACTION_KEY] = value;
}
else
{
CallContext.SetData(TRANSACTION_KEY, value);
}
}
}
/// <summary>
/// If within a web context, this uses <see cref="HttpContext" /> instead of the WinForms
/// specific <see cref="CallContext" />. Discussion concerning this found at
/// http://forum.springframework.net/showthread.php?t=572.
/// </summary>
private ISession ContextSession
{
get
{
if (IsInWebContext())
{
return (ISession)HttpContext.Current.Items[SESSION_KEY];
}
else
{
return (ISession)CallContext.GetData(SESSION_KEY);
}
}
set
{
if (IsInWebContext())
{
HttpContext.Current.Items[SESSION_KEY] = value;
}
else
{
CallContext.SetData(SESSION_KEY, value);
}
}
}
private bool IsInWebContext()
{
return HttpContext.Current != null;
}
private const string TRANSACTION_KEY = "CONTEXT_TRANSACTION";
private const string SESSION_KEY = "CONTEXT_SESSION";
private ISessionFactory sessionFactory;
}
Got this off some NHibernate gurus website - though I can't remember which one - it basically tracks and reconstructs a session for you in whichever app context you are in - works great for my project.
Then you just call the standard methods on the manager:
ISession ctx = NHibernateSessionManager.Instance.GetSession();
try
{
ctx.BeginTransaction();
ctx.Update(entity);
ctx.CommitTransaction();
}
You might have a great session handling already implemented - but from the info, what you are experiencing sounds like a session problem so let me know if that helps