entity framework error - simultaneous db reads - asp.net-mvc

Question

I have a MVC page that reads data from db. Also on the page I have some image links to /MyController/Photo which also makes some reads on the db. Now the photos are being fetched by the browser "simultaneously" so I notice that some photos don't show up and I also logged some errors:
System.NullReferenceException Object reference not set to an instance of an object.
at System.Data.SqlClient.SqlConnection.TryOpenInner(TaskCompletionSource`1 retry)
at System.Data.SqlClient.SqlConnection.TryOpen(TaskCompletionSource`1 retry)
at System.Data.SqlClient.SqlConnection.Open()
at System.Data.EntityClient.EntityConnection.OpenStoreConnectionIf(Boolean openCondition, DbConnection storeConnectionToOpen, DbConnection originalConnection, String exceptionCode, String attemptedOperation, Boolean& closeStoreConnectionOnFailure)
at System.Data.EntityClient.EntityConnection.Open()
......
Here is my code:
In the view:
<img src="#Url.Action("Photo", "Profile", new { type = "listing", uID = f.uID })" />
In the controller action:
public ActionResult Photo(string type, int uID)
{
User u = null;
if (uID == 0)
u = Repository.repository.GetUserByName(User.Identity.Name);
else
u = Repository.repository.GetUserByID(uID);
if (u != null)
{
...
}
}
My question how can I synchronize the entity framework access to the context to make sure I don't get these errors?

Answer 1

I do this with IoC/Dependancy Injection and a singleton DatabaseFactory that gets passed into each repository. The DatabaseFactory class holds the only DbContext for the site, this way there is only one and don't get into any weird issues. And I also inject my repositories into my controllers.. I'm just lazy like that.
DatabaseFactory
public class DatabaseFactory : Disposable, IDatabaseFactory
{
private CragDbContext _dataContext;
private string _connectionString;
public string ConnectionString
{
get { return _connectionString; }
set { _connectionString = value; }
}
public DatabaseFactory(string connectionString)
{
if (connectionString == null)
throw new ArgumentNullException("connectionString");
_connectionString = connectionString;
}
public CragDbContext Get()
{
if (string.IsNullOrEmpty(_connectionString))
return _dataContext ?? (_dataContext = new CragDbContext());
return _dataContext ?? (_dataContext = new CragDbContext(_connectionString));
}
protected override void DisposeCore()
{
if (_dataContext != null)
_dataContext.Dispose();
}
}
BaseRepository (that all my respositories inherit from)
public class BaseRepository<T> : IRepository<T> where T : BaseEntity
{
protected CragDbContext DbContext;
protected readonly IDbSet<T> DbSet;
protected IDatabaseFactory DatabaseFactory { get; private set; }
protected CragDbContext Context
{
get { return DbContext ?? (DbContext = DatabaseFactory.Get()); }
}
#region Ctor
public BaseRepository(IDatabaseFactory databaseFactory)
{
if (databaseFactory == null)
throw new ArgumentNullException("databaseFactory");
DatabaseFactory = databaseFactory;
DbSet = Context.Set<T>();
}
#endregion
public virtual void Add(T entity)
{
DbSet.Add(entity);
}
.... etc
}
I actually have a UnitOfWork class in the middle, but you can do it without that. Hope this helps.