Generic Repository and Transaction

Question

I have implemented my first Generic repository in MVC app. Works fine but how to put repositories in Transaction scope?

 public interface IRepository<TEntity> where TEntity : class
    {
        List<TEntity> FetchAll();
        IQueryable<TEntity> Query { get; }
        void Add(TEntity entity);
        void Delete(TEntity entity);
        void Save();
    }


    public class Repository<T> : IRepository<T> where T : class
    {
        private readonly DataContext _db;

        public Repository(DataContext db)
        {
            _db = db;
        }

        #region IRepository<T> Members

        public IQueryable<T> Query
        {
            get { return _db.GetTable<T>(); }
        }

        public List<T> FetchAll()
        {
            return Query.ToList();
        }

        public void Add(T entity)
        {
            _db.GetTable<T>().InsertOnSubmit(entity);
        }

        public void Delete(T entity)
        {
            _db.GetTable<T>().DeleteOnSubmit(entity);
        }

        public void Save()
        {
            _db.SubmitChanges();
        }

        #endregion
    }

        private void RegisterDependencyResolver()
        {
            var kernel = new StandardKernel();         
            var connectionString = ConfigurationManager.ConnectionStrings["ConnectionString"].ConnectionString;
            kernel.Bind(typeof(DataContext)).ToMethod(context => new DataContext(connectionString));
            kernel.Bind(typeof(IRepository<>)).To(typeof(Repository<>));            
            DependencyResolver.SetResolver(new NinjectDependencyResolver(kernel));
        }


    public class AdminController : Controller
    {

        private readonly IRepository<User> _userRepository;
        private readonly IRepository<Order> _orderRepository;

public AdminController(IRepository<User> userRepository, IRepository<Order> orderRepository)
        {
            _userRepository = userRepository;
            _orderRepository = orderRepository;
        }






 public ActionResult InsertUser(UserViewModel model)
        {

//Skip Code
//Do not commit data to database if _orderRepository is failed to save data
       _userRepository.Add(user);
            _userRepository.Save();


//Skip Code
      _orderRepository.Add(order);
            _orderRepository.Save();

}


}

What would be best method to wrap repository code with Transaction scope in InsertUser action?

Answer 1

You are missing an abstraction here. You should place all your business logic inside command handlers and create a command handler decorator that implements transaction behavior. This article describes how to do this, but in short:

1. Define an ICommandHandler<TCommand> interface:

   public interface ICommandHandler<TCommand>
   {
       void Handle(TCommand command);
   }
   

2. Create commands that define the contract of a business operation. Commands are simply DTOs (with only data and no behavior). For instance:

   public class ShipOrderCommand
   {
       public int OrderId { get; set; }
   
       public ShippingInfo Info { get; set; }
   }
   

3. Implement command handlers that will contain the business logic / behavior for those commands:

   public class ShipOrderCommandHandler 
       : ICommandHandler<ShipOrderCommand>
   {
       private readonly IRepository<Order> repository;
   
       public ShipOrderCommandHandler(
           IRepository<Order> repository)
       {
           this.repository = repository;
       }
   
       public void Handle(ShipOrderCommand command)
       {
           // do some useful stuf with the command and repository.
       }
   }
   

4. Let your MVC Controllers depend on the ICommandHandler<T> abstraction:

   public ShipOrderController : Controller
   {
       private readonly ICommandHandler<ShipOrderCommand> handler;
   
       public ShipOrderController(
           ICommandHandler<ShipOrderCommand> handler)
       {
           this.handler = handler;
       }
   
       public void Ship(int orderId, ShippingInfo info)
       {
           this.handler.Handle(new ShipOrderCommand
           {
               OrderId = orderId,
               Info = info
           });
       }
   }
   

5. Define a generic decorator that implements transaction logic:

   public TransactionalCommandHandlerDecorator<TCommand>
       : ICommandHandler<TCommand>
   {
       private ICommandHandler<TCommand> decoratedHandler;
   
       public TransactionalCommandHandlerDecorator(
           ICommandHandler<TCommand> decoratedHandler)
       {
           this.decoratedHandler = decoratedHandler;
       }
   
       public void Handle(TCommand command)
       {
           using (var scope = new TransactionScope())
           {
               this.decoratedHandler.Handle(command);
               scope.Complete();
           }
       }
   }
   

6. Ensure that each ShipOrderCommandHandler is decorated with a TransactionalCommandHandlerDecorator and injected into ShipOrderController. You can do this with your favorite DI container, or by hand:

   protected override IController GetControllerInstance(
       RequestContext requestContext, Type controllerType)
   {
       if (controllerType == typeof(ShipOrderController))
       {
           return new ShipOrderController(
               new TransactionalCommandHandlerDecorator<ShipOrderCommand>(
                   new ShipOrderCommandHandler(
                       new OrderRepository())));
       }
   
       return base.GetControllerInstance(requestContext, controllerType);
   }
   

With this in place you can run all your business logic inside a transaction, without the need for the business logic to be aware of that.