IOC Containers - Part 3

A little thinking after the last post lead me to the idea of persisting objects beyond the scope of a running program, a super singleton. Because an IOC container abstracts the source, and in some ways the lifespan, of an object, there is nothing stopping me from persisting the object and using it between application instances or other systems. The code would never have to know.

I used db4o in my code because of the simplicity, and native object storage. If you have never used db4o, I suggest it.

Also, this provider required explicit disposal, so I went back and implemented IDisposable on the Repository and the SingleServiceProvider.

Usage:

    var r = new Repository();

    r.RegisterServiceProvider(new SingleServiceProvider());

    r.Register<IObjectContainer, SingleServiceProvider>(() => Db4oFactory.OpenFile("test.db"));
    r.RegisterServiceProvider(new DB4OSingleServiceProvider(r.GetInstance<IObjectContainer>()));

    r.Register<IMyClass, DB4OSingleServiceProvider>(() => new MyClass("a"));

    IMyClass m = r.GetInstance<IMyClass>();

    r.Dispose();

Code:

    public class DB4OSingleServiceProvider : IRepositoryServiceProvider, IDisposable
    {
        private readonly Dictionary<Type, object> objects = new Dictionary<Type, object>();
        private readonly IObjectContainer container;

        public DB4OSingleServiceProvider(IObjectContainer container)
        {
            this.container = container;
        }

        ~DB4OSingleServiceProvider() { this.Dispose(false); }

        public void Remove(Type targetType)
        {
            var resultSet = this.container.Query(targetType);
            while (resultSet.HasNext())
            {
                this.container.Delete(resultSet.Next());
            }
            this.container.Commit();
        }

        public void Update(object o)
        {
            this.container.Store(o);
        }

        #region IRepositoryServiceProvider Members

        public void RegisterService(Type targetType, FactoryDelegate factoryMethod)
        {
            var resultSet = this.container.Query(targetType);
            if (resultSet.Count < 1)
            {
                this.container.Store(factoryMethod());
            }
        }

        #endregion

        #region IServiceProvider Members

        public object GetService(Type serviceType)
        {
            return this.container.Query(serviceType).Next();
        }

        #endregion

        [ IDisposable Members … ]
    }

I have not resolved how to handle events when the object has not been re-hydrated or dealing with multiple applications touching the same object database. Perhaps I will think about that some other time.

The biggest thing I have learned from this is that building something myself helps me understand. Now I am going to to try Autofac.