Entity Framework Context in Singleton

Question

I'm building a App that use Context of EF in Singleton Pattern like NHibernate work with Session:

public class DbContextFactory
{
    private static volatile DbContextFactory _dbContextFactory;
    private static readonly object SyncRoot = new Object();
    public DbContext Context;

    public static DbContextFactory Instance
    {
        get
        {
            if (_dbContextFactory == null)
            {
                lock (SyncRoot)
                {
                    if (_dbContextFactory == null)
                        _dbContextFactory = new DbContextFactory();
                }
            }
            return _dbContextFactory;
        }
    }

    public DbContext GetOrCreateContext()
    {
        if (this.Context == null)
            this.Context = new DbContext(ConfigurationManager.AppSettings["DefaultConnectionString"]);

        return Context;
    }
}

I'm using Ninject to Inject the Context:

public class DbContextModule : NinjectModule
{
    public override void Load()
    {
        Bind<IDbContext>().ToConstant(DbContextFactory.Instance.GetOrCreateContext());
    }
}

I'm reading about that approach and some people are saying that is bad practice and I'll have problems.

Someone that know about this with EF can explain me in more details?

Solution

NHibernate doesn't use Session as singleton ... Such scenario has only meaning in very rare cases where your application is very short batch representing single transaction / unit of work.

Here are described reasons why you should not use shared / long living context. In case of multithreaded or server application serving multiple clients you must not use shared context.

Comments

[Gert Arnold]

Did you only read it's bad practice? Without explanation?

[Acaz Souza]

What's Singleton in NHibernate? The SessionFactory?

[Acaz Souza]

Look at my approach, exist any problem? I can say to Ninject use in a RequestScope.

[Ladislav Mrnka]

Yes the factory can be used as a singleton and create a new Session each time it is required. Request scope is normally used for context in web application scenarios.

[Acaz Souza]

I'm confusing, look at my approach, I'm resolving the problem put InRequestScope in Ninject Configuration?

[Ladislav Mrnka]

I don't see any request scope in your code and still using your singleton factory in request scope will not solve it because it will return the same context instance every time.

[Acaz Souza]

please, you can fix my code using a context in request scope? Or have some code of example? Thanks, I'll very grateful;

[Ladislav Mrnka]

You must not use ToConstant. You must use To like: Bind<IDbContext>().To<YourDerivedContext>().InRequestScope()

[Onots]

Please add the relevant parts of the article to your answer. That way if the link fails your answer will still make sense.

[Pétur Ingi Egilsson]

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