In this recipe, I'll show you how we can set up the data access layer to wrap all data access in NHibernate transactions automatically.
Complete the Eg.Core model and mappings from Chapter 1.
- Create a new class library named
Eg.Core.Data. - Add a reference to
NHibernate.dlland theEg.Coreproject. - Add the following two DAO classes:
public class DataAccessObject<T, TId> where T : Entity<TId> { private readonly ISessionFactory _sessionFactory; private ISession session { get { return _sessionFactory.GetCurrentSession(); } } public DataAccessObject(ISessionFactory sessionFactory) { _sessionFactory = sessionFactory; } public T Get(TId id) { return Transact(() => session.Get<T>(id)); } public T Load(TId id) { return Transact(() => session.Load<T>(id)); } public void Save(T entity) { Transact(() => session.SaveOrUpdate(entity)); } public void Delete(T entity) { Transact(() => session.Delete(entity)); } private TResult Transact<TResult>(Func<TResult> func) { if (!session.Transaction.IsActive) { // Wrap in transaction TResult result; using (var tx = session.BeginTransaction()) { result = func.Invoke(); tx.Commit(); } return result; } // Don't wrap; return func.Invoke(); } private void Transact(Action action) { Transact<bool>(() => { action.Invoke(); return false; }); } } public class DataAccessObject<T> : DataAccessObject<T, Guid> where T : Entity { }
NHibernate requires that all data access occurs inside an NHibernate transaction. As we saw with the Transaction action filter recipe in Chapter 4, this can be easily accomplished with AOP.
This recipe shows a more explicit approach. To ensure that at least all our data access layer calls are wrapped in transactions, we create a private
Transact function that accepts a delegate, consisting of some data access methods, such as
session.Save or session.Get
. This Transact function first checks if the session has an active transaction. If it does, Transact simply invokes the delegate. If it doesn't, it creates an explicit NHibernate transaction, then invokes the delegate, and finally commits the transaction. If the data access method throws an exception, the transaction will be rolled back automatically as the exception bubbles up through the
using block.
This transactional auto-wrapping can also be set up using SessionWrapper from the unofficial NHibernate AddIns project at
http://code.google.com/p/unhaddins. This class wraps a standard NHibernate session. By default, it will throw an exception when the session is used without an NHibernate transaction. However, it can be configured to check for and create a transaction automatically, much in the same way I've shown you here. This is the same SessionWrapper we used in the Conversation per Business Transaction recipe in Chapter 3.