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?

Did you *only* read it's bad practice? Without explanation? – Gert Arnold May 06 '14 at 08:07 — Gert Arnold, May 06 '14 at 08:07

score 3 · Answer 1 · edited May 23 '17 at 12:13

3

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.

edited May 23 '17 at 12:13

Community

1
1

answered Sep 21 '11 at 11:59

Ladislav Mrnka

349,807
56
643
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What's Singleton in NHibernate? The SessionFactory? – Acaz Souza Sep 21 '11 at 12:07
Look at my approach, exist any problem? I can say to Ninject use in a RequestScope. – Acaz Souza Sep 21 '11 at 12:08
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. – Ladislav Mrnka Sep 21 '11 at 12:10
I'm confusing, look at my approach, I'm resolving the problem put InRequestScope in Ninject Configuration? – Acaz Souza Sep 21 '11 at 12:27
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. – Ladislav Mrnka Sep 21 '11 at 12:34
please, you can fix my code using a context in request scope? Or have some code of example? Thanks, I'll very grateful; – Acaz Souza Sep 21 '11 at 12:38
You must not use `ToConstant`. You must use `To` like: `Bind().To().InRequestScope()` – Ladislav Mrnka Sep 21 '11 at 13:00

score 0 · Answer 2 · answered May 06 '14 at 07:48

0

You read this article. Why you shouldn't use singleton DataContexts in Entity Framework? http://www.britishdeveloper.co.uk/2011/03/dont-use-singleton-datacontexts-entity.html

answered May 06 '14 at 07:48

Marcos

19
1

10

Please add the relevant parts of the article to your answer. That way if the link fails your answer will still make sense. – Onots May 06 '14 at 08:13

score 0 · Answer 3 · answered Feb 08 '18 at 08:02

public class Dock
{
    // Statik field
    private static Dock _dock;
    // lock object
    private static object lockObject = new object();

    // We prevent the constructive method from being modeled with new by 
    //making it secret.
    private Dock()
    {

    }
    // Class in Instance
    public static Dock Instance()
    {   
        if (_dock == null)
        {
            lock (lockObject)
            {
                if (_dock == null)
                    _dock = new Dock();
            }
        }
        return _dock;
    }

}

meziantou · Answer 4 · 2011-09-21T12:10:01.553

A good pratice is to use a datacontext per unit of work To have more information about unit of work with EF you should read http://blogs.msdn.com/b/adonet/archive/2009/06/16/using-repository-and-unit-of-work-patterns-with-entity-framework-4-0.aspx

When sharing the same datacontext you are probably saving a few 10s of milliseconds. The word micro optimisation springs to mind - in which case you probably shouldn't be using Entity Framework.

Having a DataContext that is never closed allows you to lazy load whenever you want. You may have left your Service and now be in your Controller or worse still, your View. Accessing the database from a View is asking for performance problems as I'm sure you didn't allow that intentionally. It is most likely because you forgot to eager load all the data you need to populate your view.

Article no longer available. – Pétur Ingi Egilsson Mar 26 '17 at 18:02 — Pétur Ingi Egilsson, Mar 26 '17 at 18:02

Entity Framework Context in Singleton

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