Question

Following the directions from many articles, I’ve decided to implement the Unit of work pattern to my Linq2SQL DataContexts in my ASP.Net WebForms Application, but I’m not sure if I’m on the right way.

Here’s what I’m accomplishing so far:

1 – On every Request, I catch the Application_AcquireRequestState event (which has access to Session data) in Global.asax and instantiate a new DataContext to bind it to the user’s Session:

void Application_AcquireRequestState(object sender, EventArgs e)
{
    // Check if the request is for a Page, Page Method or Handler
    if (new Regex(@"\.(aspx|ashx)(/.*)?$").IsMatch(HttpContext.Current.Request.Url.AbsolutePath))
    {
        MyCompany.MyDatabaseDataContext myDatabaseDataContext = new MyCompany.MyDatabaseDataContext();

        HttpContext.Current.Session["myDatabaseDataContext"] = myDatabaseDataContext;
    }
}

2 – Every Data Access Layer Object (DAO) inherits from a base DAO: GenericDAO:

public class GenericDAO
{
    private MyDatabaseDataContext _dbMyDatabase;

    protected MyDatabaseDataContext dbMyDatabase
    {
        get
        {
            if (_dbMyDatabase == null)
                _dbMyDatabase = HttpContext.Current.Session["myDatabaseDataContext"] as MyDatabaseDataContext;

            return _dbMyDatabase;
        }
    }
}

3 – So, in every operation, the DAO use the DataContext Property from its parent class:

public class MyTableDAO : GenericDAO
{
    public List<MyTable> getAll()
    {
        return dbMyDatabase.GetTable<MyTable>().ToList();
    }
}

Here’s my concerns…

1. First of all, is it ok to store the DataContext in the user’s Session? What would be another option? My app has a lot of PageMethods calls, so I’m worried the DTX would be invalidated between their async requests if it is stored in the session.
2. Do I need to capture the Application_ReleaseRequestState event to Dispose() of the DataContext and remove it from the session?
3. If I don’t need to Dispose of it, in every Application_AcquireRequestState, would it be better to Remove DTX from Session - Create DTX - Store it or just Refresh it?
4. Also, if I don’t need to Dispose of it, what about Connections? Would it handle them automatically or I would need to control them too?

I appreciate your time and help 🙂

— EDIT

Here’s the code I’ve reached, following @ivowiblo’s suggestion:

Global.asax

void Application_BeginRequest(object sender, EventArgs e)
{
    if (new Regex(@"\.(aspx|ashx)(/.*)?$").IsMatch(HttpContext.Current.Request.Url.AbsolutePath))
    {
        MyCompany.MyDatabaseDataContext myDatabaseDataContext = new MyCompany.MyDatabaseDataContext();

        HttpContext.Current.Items["myDatabaseDataContext"] = ceabsDataContext;
    }
}

void Application_EndRequest(object sender, EventArgs e)
{
    if (new Regex(@"\.(aspx|ashx)(/.*)?$").IsMatch(HttpContext.Current.Request.Url.AbsolutePath))
    {
        if (HttpContext.Current.Items["myDatabaseDataContext"] != null)
        {
            System.Data.Linq.DataContext myDbDtx = HttpContext.Current.Items["myDatabaseDataContext"] as System.Data.Linq.DataContext;

            if (myDbDtx != null)
                myDbDtx.Dispose();
        }
    }
}

GenericDAO

public class GenericDAO
{
    protected MyDatabaseDataContext dbMyDatabase
    {
        get
        {
            return HttpContext.Current.Items["myDatabaseDataContext"] as MyDatabaseDataContext;
        }
    }
}

Simple as that!

Answer 1

The best approach is to put it on HttpContext.Current.Items, creating the DataContext on RequestBegin and dispose it in RequestEnd. In msdn there’s an interesting article about the better management of the DataContext, where it’s suggested to have short-time DataContext instances.

This pattern is called Open session in view and was created for using NHibernate in web environments.