unable to query EntityFramework shared dbcontext reliably

Question

I'm trying to share a simple DbContext with 4 DbSets among multiple repositories, each of my repositories inherit from this base class

 public class CodeFirstRepository : IDisposable
    {
        private static MyContext _ctx = new MyContext();
        protected MyContext Context
        {
            get { return _ctx; }
        }

        public void Dispose()
        {
            if (Context != null)
            {
                Context.Dispose();
            }
        }
    }

Question: is this an appropriate way to share a connection between repositories?

I'm getting intermittent failures in my unit tests when accessing the various repositories. An exception is thrown from the repository method GetEntityByName

public IOfferResult GetEntityByName(string name)
{
   return Context.Entities.Where(o => o.Name == name).FirstOrDefault()
}

Test method Tests.Service.TestDelete threw exception: System.ObjectDisposedException: The ObjectContext instance has been disposed and can no longer be used for operations that require a connection.

if the database already exists, the code executes as expected. it also works when i change the implementation of GetEntityByName(string name) to the following non-performant code

public IOfferResult GetEntityByName(string name)
{
   foreach (OfferResult offer in Context.Offers)
   {
       if (offerName.ToLower() == offer.Name.ToLower())
       {
           return offer;
       }
   }
}

Question: what is going on here?

bear in mind that if the database exists when i run the tests i don't get the error at all.

tia, jt

StriplingWarrior · Accepted Answer · 2011-10-04T17:56:54.633

This problem is arising because you are treating the DbContext like a singleton by declaring it as a static field, but then you are treating it like it like a transient instance by disposing it as soon as any instance of CodeFirstRepository gets disposed. For example:

using (var r = new PersonRepository())
{
   // do something
} // When you hit the end of this block, your static DbContext is disposed.
using (var r = new IOfferRepository())
{
    r.GetEntityByName("test"); // this will fail because the context is still disposed.
}

You should not share contexts this way. If you really want all of your repositories to use a single instance of the DbContext, remove the call to Context.Dispose(). This would fix the problem you're getting right now, but it will likely introduce other problems in the future.

But I would strongly caution against using a single DbContext in a scenario where multiple threads could be trying to access it simultaneously. According to the DbContext specs:

Any instance members are not guaranteed to be thread safe.

You'd be better off just removing the static keyword from your field.

would injecting the context class into the repositories using UnityContainer and the transient lifecycle be a better alternative? also can you tell me why it's considered poor form? — Jason, Oct 04 '11 at 17:48
@Jason: I fleshed out my answer a little. The most important thing is to not have the field be static. Beyond that, I would say dependency injection is preferable to instantiating it directly. You can use a transient lifecycle and continue disposing it with your repository. That would probably be simplest. There are other strategies (per-request if it's a web app, e.g.) that could work, but unless you can guarantee you won't try accessing the context from multiple threads at once, the transient lifecycle is the safest. — StriplingWarrior, Oct 04 '11 at 18:02

unable to query EntityFramework shared dbcontext reliably

1 Answers1