Simple Convention Automapper for two-way Mapping (Entities to/from ViewModels)

Question

UPDATE: this stuff has evolved into a nice project, see it at http://valueinjecter.codeplex.com

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check this out, I just wrote a simple automapper, it takes the value from the property with the same name and type of one object and puts it into another, and you can add exceptions (ifs, switch) for each type you may need

so tell me what do you think about it ?

I did it so I could do something like this:

Product –> ProductDTO

ProductDTO –> Product

that's how it begun:

I use the "object" type in my Inputs/Dto/ViewModels for DropDowns because I send to the html a IEnumerable<SelectListItem> and I receive a string array of selected keys back

 public void Map(object a, object b)
    {
        var pp = a.GetType().GetProperties();
        foreach (var pa in pp)
        {
            var value = pa.GetValue(a, null);

            // property with the same name in b
            var pb = b.GetType().GetProperty(pa.Name);
            if (pb == null)
            {
                //no such property in b
                continue;
            }

            if (pa.PropertyType == pb.PropertyType)
            {
                pb.SetValue(b, value, null);
            }

        }
    }

UPDATE: the real usage:
the Build methods (Input = Dto):

        public static TI BuildInput<TI, T>(this T entity) where TI: class, new()
        {
            var input = new TI();
            input = Map(entity, input) as TI;
            return input;
        }

        public static T BuildEntity<T, TI, TR>(this TI input)
            where T : class, new()
            where TR : IBaseAdvanceService<T>
        {               
            var id = (long)input.GetType().GetProperty("Id").GetValue(input, null);
            var entity = LocatorConfigurator.Resolve<TR>().Get(id) ?? new T();
            entity = Map(input, entity) as T;
            return entity;
        }

        public static TI RebuildInput<T, TI, TR>(this TI input)
            where T: class, new()
            where TR : IBaseAdvanceService<T>
            where TI : class, new()
        {

                return input.BuildEntity<T, TI, TR>().BuildInput<TI, T>();
            }

in the controller:

    public ActionResult Create()
    { 
        return View(new Organisation().BuildInput<OrganisationInput, Organisation>());
    }

    [AcceptVerbs(HttpVerbs.Post)]
    public ActionResult Create(OrganisationInput o)
    {
        if (!ModelState.IsValid)
        {
            return View(o.RebuildInput<Organisation,OrganisationInput, IOrganisationService>());                
        }
        organisationService.SaveOrUpdate(o.BuildEntity<Organisation, OrganisationInput, IOrganisationService>());
        return RedirectToAction("Index");
    }

The real Map method

public static object Map(object a, object b)
        {
            var lookups = GetLookups();

            var propertyInfos = a.GetType().GetProperties();
            foreach (var pa in propertyInfos)
            {
                var value = pa.GetValue(a, null);

                // property with the same name in b
                var pb = b.GetType().GetProperty(pa.Name);
                if (pb == null)
                {
                    continue;
                }

                if (pa.PropertyType == pb.PropertyType)
                {
                    pb.SetValue(b, value, null);
                }
                else if (lookups.Contains(pa.Name) && pa.PropertyType == typeof(LookupItem))
                {
                    pb.SetValue(b, (pa.GetValue(a, null) as LookupItem).GetSelectList(pa.Name), null);
                }
                else if (lookups.Contains(pa.Name) && pa.PropertyType == typeof(object))
                {
                    pb.SetValue(b, pa.GetValue(a, null).ReadSelectItemValue(), null);
                }
                else if (pa.PropertyType == typeof(long) && pb.PropertyType == typeof(Organisation))
                {
                    pb.SetValue(b, pa.GetValue<long>(a).ReadOrganisationId(), null);
                }
                else if (pa.PropertyType == typeof(Organisation) && pb.PropertyType == typeof(long))
                {
                    pb.SetValue(b, pa.GetValue<Organisation>(a).Id, null);
                }
            }

            return b;
        }

Answer 1

One thing you might want to add is to cache the reflection bits. If you map an object twice, you probably don't want to look up all the reflection stuff again. Also, things like GetValue and SetValue are quite slow, I switched to late-bound delegates + Reflection.Emit to speed things up.