DD4T model builders must die. But before that they must learn to play nicely with Unity DI. Here's how.

BuilderFactory.cs

using System;
using System.Collections.Generic;
using System.Linq;
using Microsoft.Practices.ServiceLocation;
using Microsoft.Practices.Unity;

namespace Alitalia.ConsumerWeb.Mapping.Tridion
{
    public class BuilderFactory
    {
        private static readonly IDictionary<string, IBuilder> BuilderCache = new Dictionary<string, IBuilder>();

        private static IUnityContainer container;

        public static IBuilder GetBuilder(string viewName)
        {
            IBuilder builder;

            if (!BuilderCache.TryGetValue(viewName, out builder))
            {
                Type builderType = typeof(BuilderFactory).Assembly.GetTypes()
                    .FirstOrDefault(t => typeof(IBuilder).IsAssignableFrom(t) && t.Name.StartsWith(viewName));
                
                if (builderType != null)
                {
                    builder = GetContainer().Resolve(builderType) as IBuilder;
                    if (builder != null)
                        BuilderCache.Add(viewName, builder);
                }
            }

            return builder;
        }

        private static IUnityContainer GetContainer()
        {
            return container ?? (container = ServiceLocator.Current.GetInstance<IUnityContainer>());
        }
    }
}