The unit of work pattern within a asp.net mvc application

Question

I have been looking at this excellant blog titled "NHibernate and the Unit of Work Pattern" and have a question regarding the best place to use UnitOfWork.Start in a asp.net mvc project.

My SLN is broken down into the following projects:-

 MVC project
 Repository
 NHibernateUnitOfWork

I have an interface:-

 public interface INameRepository
 ...
       IList<Name> GetByOrigin(int OriginId)
 ...

I have a concrete implementation

     public class NameRepository : INameRepository
     ...
          public  IList<Name> GetByOrigin(int OriginId) {
                using (UnitOfWork.Start()) {
                     var query = session.Linq<...
                     return query;
                }
          }
     ...

My question is do I wrap all my methods inside all my repositories with using(UnitOfWork.Start()) or is there a better approach?

I am using nHibernate, asp.net mvc.

Answer 1

I think Sharp Architecture solves this quite well. What they do is put the unit of work inside an ASP .Net MVC Action Filter. Basically you can define a transaction Action filter such as

public class TransactionAttribute : ActionFilterAttribute
{
      public override void OnActionExecuting(ActionExecutingContext filterContext)
      {
         UnitOfWork.Start();
      }

      public override void OnActionExecuted(ActionExecutedContext filterContext)
      {
         UnitOfWork.Stop();
      }
}

and in your controller class put the Transaction attribute on your Action Result method

Answer 2

With the unit of work pattern, you don't put every dataaccess method in a separate unit of work. You use the unit of work around the whole work that needs to be done, which is in most cases in a web application a webrequest. The idea is that a request can fail, or succeed. When you add 2 items to the database during one request, the should be both added, or not. Not just one of them. In most cases, the easiest way to start a unit of work in a mvc (or other web) application is in the begin and end request methods of the global.asax

class Global
{
    BeginRequest()
    {
        servicelocater.get<unitofwork>().start();
    }

    EndRequest()
    {
        var unit = servicelocater.Get<Unitofwork>();
        try
        {
            unit.commit();
        }
        catch
        {
            unit.rollback();
            throw;
        }
    }
}

class Repository<T>
{
     public Repository(INHibernateUnitofwork unitofwork)
     {
         this.unitofwork = unitofwork;
     }

     public void Add(T entity)
     {
         unitofwork.session.save(entity);
     }
}