Adam Finzel

Do developers make things hard for themselves and fellow developers

Today has made me wonder if we are doing something wrong as developers. This weekend I gave myself two tasks. The first was to replace some immersion heaters. (Ours had stopped working and we have been without hot water for a couple of weeks. The shower and washing machine heat their own water so it hadn’t been a huge priority.) The second was to do some more work on a private project to try and get my head more around windsor, nhibernate, etc.

The immersion heater was relatively painless. I found, http://www.ultimatehandyman.co.uk/plumb_immersion_heater.htm on the internet which armed me with enough knowledge to go to screwfix direct and buy the bits. So the process was:

1. Buy bits.
2. Unwire old heaters
3. Remove heaters (this took a while as they didn’t want to budge)
4. Screw new heaters in.
5. Wire them back up.
6. Try and plug leak with sealant

The whole process was relatively painless and I never felt like I didn’t know what I was doing or felt like hitting my head against a wall. Now the second task my private project, wire up automapper and write data to a repository. I see automapper as a component, just like the immersion heater. If you don’t know Automapper is an awsome library that will try its best to map from one object to another without having to say object1.FieldX maps to object2.FieldX.

So the first step to get automapper to work is to register the mappers. Some googling later brings up this suggestion:

 public static class AutoMapperRegistrar 
    {
       public static void RegisterMappings()
       {
           var autoMapperClasses = Assembly.GetAssembly(typeof(AutoMapperRegistrar)).GetTypes().Where(t => String.Equals(t.Namespace, "restaurantBooker.Automapper.Maps", StringComparison.Ordinal));
           
           foreach (var autoMapperClass in autoMapperClasses)
           {
               autoMapperClass.InvokeMember(
                    "CreateMap",
                    BindingFlags.InvokeMethod | BindingFlags.Instance | BindingFlags.Public |
                        BindingFlags.Static,
                    null,
                    null,
                    null);
           }
       }

    }

So far so good. I add the relevant classes and I get my basic mapping working. I now have my objects mapping nicely. I try to save my object to the repository only to find I have forgotten to add a resolver to map from an Id to an entity in the database. I had done this at work so a quick google on resolveusing, refreshes my memory and I create a resolver.

public class RestaurantResolver : ValueResolver
    {
        private INHibernateRepository _restaurantRepository;

        public RestaurantResolver(INHibernateRepository restaurantRepository)
        {
            _restaurantRepository = restaurantRepository;
        }
      
        protected override Restaurant ResolveCore(int source)
        {
            return _restaurantRepository.Load(source);
        }
    }

and update my mapping file

 public class Table_KoViewModelsTable : BaseMapper, ITable_KoViewModelsTable
    {
        
        private readonly INHibernateRepository _restaurantRepository;

      
        public Table_KoViewModelsTable(INHibernateRepository restaurantRepository)
        {
            _restaurantRepository = restaurantRepository;
        }

        protected override void CreateMap()
        {
            Mapper.CreateMap();
            Mapper.CreateMap()
                .ForMember(dest => dest.Restaurant, opt => opt
                                                            .ResolveUsing()
                                                            .FromMember(src => src.RestaurantId)
                                                            .ConstructedBy(() => new RestaurantResolver(_restaurantRepository))
                                                            );
        }

       
    }

So I run the code and find that _restaurantRepository is null. So the _restaurantRepository should be injected in by Castle Windsor but because I am using reflection to call the createMap, it doesn’t inject. After around an hours worth of googling, I draw blanks so I log onto work and see how we do it there. I then spent around another 40 minutes trying to work out how the create map is working. Eventually I find that all the mappers derive from a base mapper which has a constructor which setups the mappers. During the component registration, castle windsor runs the constructors on each of the classes, thus creating the maps. I then went on to create a similar setup and at last I have it working.

So whats my point?

Well with the immersion heater, the immersion heaters diameters are standard. Wiring the heater up consists of 3 wires, each are standardized in their colours. You can get either 11″ or 22″ in length immersion heaters but its obvious which one will fit in the boiler. Now if we look at the fun with automapper and windsor, we find that we have significantly more ways that we can implement these libraries, not all of which solve all the problems, so we have to play about to try and get the right combination that works for us. I think design patterns goes some way to help us try and standardize our code but this doesn’t help with implementation. When we design our code it is designed to be consumed in different ways. Sometimes I do wonder if we should try and have more standard ways of using libraries. After all if I can fit an immersion heater after reading one web page, it does suggest that as developers we make things difficult for ourselves.