Unit of work, generic repository and business layer

Question

First sorry if this was asked already but i cannot find an answer for this 'particular case'.

I've a Interface of Unit of Work:

public interface IUnitOfWork
{
    DbContext Context { get; set; }
    void Dispose();
    void Save();
}

And use a Generic Repository class:

public class GenericRepository<TEntity> where TEntity : class
    {

        private DbSet<TEntity> dbSet;

        private IUnitOfWork UnitOfWork { get; set; }
        private DbContext context { get { return UnitOfWork.Context; } }

        public GenericRepository(IUnitOfWork unitOfWork)
        {
            UnitOfWork = unitOfWork;
            this.dbSet = context.Set<TEntity>();
        }

        public virtual IEnumerable<TEntity> Get(
            Expression<Func<TEntity, bool>> filter = null,
            Func<IQueryable<TEntity>, IOrderedQueryable<TEntity>> orderBy = null,
            string includeProperties = "")
        {
            IQueryable<TEntity> query = dbSet;

            if (filter != null)
            {
                query = query.Where(filter);
            }

            foreach (var includeProperty in includeProperties.Split
                (new char[] { ',' }, StringSplitOptions.RemoveEmptyEntries))
            {
                query = query.Include(includeProperty);
            }

            if (orderBy != null)
            {
                return orderBy(query).ToList();
            }
            else
            {
                return query.ToList();
            }
        }

        public virtual TEntity GetByID(object id)
        {
            return dbSet.Find(id);
        }

        public virtual void Insert(TEntity entity)
        {
            dbSet.Add(entity);
        }

        public virtual void Delete(object id)
        {
            TEntity entityToDelete = dbSet.Find(id);
            Delete(entityToDelete);
        }

        public virtual void Delete(TEntity entityToDelete)
        {
            if (context.Entry(entityToDelete).State == EntityState.Detached)
            {
                dbSet.Attach(entityToDelete);
            }
            dbSet.Remove(entityToDelete);
        }

        public virtual void Update(TEntity entityToUpdate)
        {
            dbSet.Attach(entityToUpdate);
            context.Entry(entityToUpdate).State = EntityState.Modified;
        }
    }

I don't want to do my logic in my MVC controler, so I added a businesslayer. My question is, where should I instantiate (and dispote) my IUnitOfWork, in my controler and pass it to my business layer? Example:

 public static class CircleLogic
    {
        public static void DeleteCircle(IUnitOfWork uow, int id)
        {
            try
            {
                var circleRep = new GenericRepository<Circle>(uow);

                var circle = circleRep.GetByID(id);
                 ......
                  circleRep.Delete(id);            

                uow.Save();

            }
            catch (Exception ex)
            {
                throw;
            }
        }
    }

I've seen this but I don't want to instantiate it in my business layer. What is the best approach?

Thanks!

Answer 1

I see no harm in passing it into your Business Layer like you have suggested. However, if you want to keep your Business Layer completely persistence ignorant I would suggest introducing an IRepository<T> interface and passing that in instead.

In terms of disposing of the objects, I would make both your IUnitOfWork /Repository classes implement IDisposable so you can make use of the using statement eg

public ActionResult DeleteCircle(int id)
{
    using (IUnitOfWork uow = new UnitOfWork())
    {
        using (IRepository<Circle> repo = new GenericRepository<Circle>(uow))
        {
            CircleLogic.DeleteCircle(repo, id);
        }
        uow.Save();
    }
}

...

public static class CircleLogic
{
    public static void DeleteCircle(IRepository<Circle> repo, int id)
    {
        var circle = repo.GetById(id);
        ...
        repo.Delete(id);
    }
}

Answer 2

Because your concrete UnitOfWork implementation would most likely live in your persistence layer, it'd be sensible to instantiate it in either the persistence layer or 1 layer above in the business layer. Your UI should have no knowledge of what technology you're using to persist your entities/data.