Generic DAO with NHibernate

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4/28/06 Update:  The NHibernate codeproject.com article wins ASP.NET article of the month.  Woohoo!
3/14/06 Update:  See how this is used in a sample application at http://www.codeproject.com/useritems/NHibernateBestPractices.asp.
 
 
Hibernate.org has a great article on creating a generic DAO for Hibernate in Java.  Below is what I use for the C# port.
 
The interface for common CRUD functionality...
 
public interface GenericDAO {
  T GetById(IdDataType id, bool shouldLock);
  List GetAll();
  List GetByExample(T exampleInstance, string[] propertiesToExclude);
  T SaveOrUpdate(T entity);
  void Delete(T entity);
}
 
The generic DAO implementation...
 
public abstract class GenericNHibernateDAO : GenericDAO
{
  /// Could be set using contruction injection IoC
  public GenericNHibernateDAO(ISessionManager sessionManager) {
    this.sessionManager = sessionManager;
  }
 
  public T GetById(IdDataType id, bool shouldLock) {
    ISession session = GetSession();
    T entity;
 
    if (shouldLock) {
      entity = (T) session.Load(persitentType, id, LockMode.Upgrade);
    }
    else {
      entity = (T) session.Load(persitentType, id);
    }
 
    return entity;
  }
 
  public List GetAll() {
    return GetByCriteria();
  }
 
  protected List GetByCriteria(params ICriterion[] criterion) {
    ISession session = GetSession();
    ICriteria criteria = session.CreateCriteria(persitentType);
    
    foreach (ICriterion criterium in criterion) {
      criteria.Add(criterium);
    }
    
    GenericUtils genericUtils = new GenericUtils();
    return genericUtils.ConvertToGenericList(criteria.List());
  }
 
  public List GetByExample(T exampleInstance, string[] propertiesToExclude) {
    ISession session = GetSession();
    ICriteria criteria = session.CreateCriteria(persitentType);
    Example example = Example.Create(exampleInstance);
 
    foreach (string propertyToExclude in propertiesToExclude) {
      example.ExcludeProperty(propertyToExclude);
    }
 
    criteria.Add(example);
 
    GenericUtils genericUtils = new GenericUtils();
    return genericUtils.ConvertToGenericList(criteria.List());
  }
 
  public T SaveOrUpdate(T entity) {
    ISession session = GetSession();
    session.SaveOrUpdate(entity);
 
    return entity;
  }
 
  public void Delete(T entity) {
    ISession session = GetSession();
    session.Delete(entity);
  }
 
  private ISession GetSession() {
    Check.Require(sessionManager != null, "sessionManager was not set");
    return sessionManager.OpenSession();
  }
 
  private Type persitentType = typeof(T);
  private ISessionManager sessionManager;
}
 
And for using this within your code...
 
public class ProjectDAONHibernate : GenericNHibernateDAO<Project, int> {
  public ProjectDAONHibernate(ISessionManager sessionManager) : base(sessionManager) {}
}
 

Notes: