Understanding and Implementing Repository and Unit of Work Pattern in ASP.NET MVC Application

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;

namespace RepoUowSample.Models
{
    public class UnitOfWork : IDisposable
    {
        private SampleDatabaseEntities entities = null;

        // This will be called from controller default constructor
        public UnitOfWork()           
        {
            entities = new SampleDatabaseEntities();
            BooksRepository = new BooksRepositoryEn(entities);
        }

        // This will be created from test project and passed on to the
        // controllers parameterized constructors
        public UnitOfWork(IBooksRepository booksRepo)
        {
            BooksRepository = booksRepo;
        }

        public IBooksRepository BooksRepository
        {
            get;
            private set;
        }

        #region IDisposable Members

        public void Dispose()
        {
            Dispose(true);
            
            GC.SuppressFinalize(this);
        }

        protected virtual void Dispose(bool disposing)
        {
            if (disposing == true)
            {
                entities = null;
            }
        }

        ~UnitOfWork()
        {
            Dispose(false);
        }

        #endregion
    }
}