Occasional "The underlying provider failed on Open" errors when using EF4 (edmx model)

Question

I hope someone can help me with a solution to the following error. The application in which the error happens is running in production and I never experience the error myself. However around 20 times a day I receive an error mail telling me:

The underlying provider failed on Open. ---> System.InvalidOperationException: The connection was not closed. The connection's current state is connecting.

Here's the stack trace

System.Data.EntityException: The underlying provider failed on Open. ---> System.InvalidOperationException: The connection was not closed. The connection's current state is connecting. at System.Data.ProviderBase.DbConnectionBusy.OpenConnection(DbConnection outerConnection, DbConnectionFactory connectionFactory) at System.Data.SqlClient.SqlConnection.Open() at HibernatingRhinos.Profiler.Appender.ProfiledDataAccess.ProfiledConnection.Open() at System.Data.EntityClient.EntityConnection.OpenStoreConnectionIf(Boolean openCondition, DbConnection storeConnectionToOpen, DbConnection originalConnection, String exceptionCode, String attemptedOperation, Boolean& closeStoreConnectionOnFailure) --- End of inner exception stack trace --- at System.Data.EntityClient.EntityConnection.OpenStoreConnectionIf(Boolean openCondition, DbConnection storeConnectionToOpen, DbConnection originalConnection, String exceptionCode, String attemptedOperation, Boolean& closeStoreConnectionOnFailure) at System.Data.EntityClient.EntityConnection.Open() at System.Data.Objects.ObjectContext.EnsureConnection() at System.Data.Objects.ObjectQuery1.GetResults(Nullable1 forMergeOption) at System.Data.Objects.ObjectQuery1.System.Collections.Generic.IEnumerable<T>.GetEnumerator() at System.Linq.Enumerable.FirstOrDefault[TSource](IEnumerable1 source) at System.Data.Objects.ELinq.ObjectQueryProvider.b__1[TResult](IEnumerable1 sequence) at System.Data.Objects.ELinq.ObjectQueryProvider.ExecuteSingle[TResult](IEnumerable1 query, Expression queryRoot) at System.Data.Objects.ELinq.ObjectQueryProvider.System.Linq.IQueryProvider.Execute[S](Expression expression) at System.Linq.Queryable.FirstOrDefault[TSource](IQueryable`1 source)
at GuideSites.DomainModel.Repositories.ClinicTermRepository.GetClinicTermByGuideSiteId(Int32 guideSiteId) in C:\Projects\GuideSites\GuideSites.DomainModel\Repositories\ClinicTermRepository.cs:line 20 at GuideSites.Web.Frontend.Helpers.VerifyUrlHelper.RedirectOldUrls() in C:\Projects\GuideSites\GuideSites.Web.Frontend\Helpers\VerifyUrlHelper.cs:line 91 at GuideSites.Web.Frontend.MvcApplication.Application_BeginRequest(Object sender, EventArgs e) in C:\Projects\GuideSites\GuideSites.Web.Frontend\Global.asax.cs:line 412 at System.Web.HttpApplication.SyncEventExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously)

I use EF4 through an EDMX model and I the way I connect to the database (MS SQL 2008) is through an HttpContext-based per-request object context so that connections to the database aren't opened and closed for every single piece of data I need on a given pageload.

My Database context class looks like this:

public class DatabaseContext : IDisposable
{
    private const string ContextName = "context";
    private static dbEntities _dbEntities;

    public dbEntities GetDatabaseContext()
    {
        SqlConnection.ClearAllPools();

        if (HttpContext.Current == null)
            return _dbEntities ?? (_dbEntities = new dbEntities());

        if (HttpContext.Current.Items[ContextName] == null)
            HttpContext.Current.Items[ContextName] = new dbEntities();

        _dbEntities = (dbEntities)HttpContext.Current.Items[ContextName];
        if (_dbEntities.Connection.State == ConnectionState.Closed)
        {
            _dbEntities.Connection.Open();
            return _dbEntities;
        }

        return _dbEntities;
    }


    public void RemoveContext()
    {
        if (HttpContext.Current != null && HttpContext.Current.Items[ContextName] != null)
        {
            ((dbEntities)HttpContext.Current.Items[ContextName]).Dispose();
            HttpContext.Current.Items[ContextName] = null;
        }

        if (_dbEntities != null)
        {
            _dbEntities.Dispose();
            _dbEntities = null;
        }
    }


    public void Dispose()
    {
        RemoveContext();
    }

}

In my repositories I use the database context like this:

public class SomeRepository
{
    private static readonly object Lock = new object();
    private readonly dbEntities _dbEntities;

    public SomeRepository()
    {
        var databaseContext = new DatabaseContext();
        _dbEntities = databaseContext.GetDatabaseContext();
    }


    public IEnumerable<SomeRecord> GetSomeData(int id)
    {
        lock (Lock)
        {
            return
                _dbEntities.SomeData.Where(c => c.Id == id);
        }
    }
 }

The lock(Lock) thing was something I read about should help this problem but in my case it hasn't. And generally it's been difficult finding threads that describe exactly my problem let alone a solution to the problem.

The application is an ASP.NET MVC3 application and it's setup as one application running for 9 different websites (the domain determines the content to be served to the client). The 9 websites doesn't have more than 2.000 pageviews daily, so the database should be stressed on that account.

I hope someone can help and please let me know if there is something I forgot to mention.

Answer 1

As per my comment, Dispose() has to be called by something at the end of the request. You can do this with an HttpModule like so:

public class ContextDisposer : IHttpModule
{
    private readonly DatabaseContext _context = new DatabaseContext();

    public void Init(HttpApplication context)
    {
        context.EndRequest += (sender, e) => this.DisposeContext(sender, e);
    }

    private static bool DoesRequestCompletionRequireDisposing(
        string requestPath)
    {
        string fileExtension = Path.GetExtension(requestPath)
            .ToUpperInvariant();

        switch (fileExtension)
        {
            case ".ASPX":
            case string.Empty:
            case null:
                return true;
        }

        return false;
    }

    private void DisposeContext(object sender, EventArgs e)
    {
        // This gets fired for every request to the server, but there's no 
        // point trying to dispose anything if the request is for (e.g.) a 
        // gif, so only call Dispose() if necessary:
        string requestedFilePath = ((HttpApplication)sender).Request.FilePath;

        if (DoesRequestCompletionRequireDisposing(requestedFilePath))
        {
            this._context.Dispose();
        }
    }
}

You then plug the module into the request pipeline like this (you put it into system.web and system.webserver so it's included for IIS and the VS dev web server):

<system.web>
    <httpModules>
        <add name="ContextDisposer" 
             type="MyNamespace.ContextDisposer" />
    </httpModules>
</system.web>

<system.webServer>
    <modules runAllManagedModulesForAllRequests="true">
        <add name="ContextDisposer" 
             type="MyNamespace.ContextDisposer" />
    </modules>
</system.webServer>