Question

My problem is hydrating a Viewmodel from a Linq2Sql object that has been returned from the database. We have done this in a few areas and have a nice layered pattern worked up for it but the latest item calls for some enums to be used and this has caused headaches all round. Currently we pull back from the database then use Automapper to hydrate (or flatten) into our Viewmodels but having the enums in the model seems to be causing issues with Automapper. I’ve tried to create custom resovlers which have sufficed for all my other mapping requirements but it doesn’t work in this instance.

A sample of the code looks like:

public class CustomerBillingTabView{
    public string PaymentMethod {get; set;}
    ...other details
}

public class BillingViewModel{
    public PaymentMethodType PaymentMethod {get; set;}
    ...other details
}

public enum PaymentMethodType {
    Invoice, DirectDebit, CreditCard, Other
}

public class PaymentMethodTypeResolver : ValueResolver<CustomerBillingTabView, PaymentMethodType>
{
    protected override PaymentMethodType ResolveCore(CustomerBillingTabView source)
    {

        if (string.IsNullOrWhiteSpace(source.PaymentMethod))
        {
            source.PaymentMethod = source.PaymentMethod.Replace(" ", "");
            return (PaymentMethodType)Enum.Parse(typeof(PaymentMethodType), source.PaymentMethod, true);
        }

        return PaymentMethodType.Other;
    }
}

        CreateMap<CustomerBillingTabView, CustomerBillingViewModel>()
        .ForMember(c => c.CollectionMethod, opt => opt.ResolveUsing<PaymentMethodTypeResolver>())

I get the following error

[ArgumentException: Type provided must be an Enum.
Parameter name: enumType]
   System.Enum.TryParseEnum(Type enumType, String value, Boolean ignoreCase, EnumResult& parseResult) +9626766
   System.Enum.Parse(Type enumType, String value, Boolean ignoreCase) +80
   AutoMapper.Mappers.EnumMapper.Map(ResolutionContext context, IMappingEngineRunner mapper) +231
   AutoMapper.MappingEngine.AutoMapper.IMappingEngineRunner.Map(ResolutionContext context) +720

I’d like to stick with Automapper for all of our mapping actions but I’ve seen a lot of people say that it doesn’t do this type of mappings so I’m starting to wonder if I’m using it in the wrong way? Also, I’ve seen a few mentions of ValueInjecter – is this an alternative to Automapper, or will it be useful to just plug the holes in Automapper for the hydration of models and use Automapper for flattening?

Yes I could just use a string in my ViewModel, but I’m not a fan of magic strings, and this particular item is used by helpers to perform some logic in a number of places.

Answer 1

This is an issue with the AutoMapper documentation. If you download the AutoMapper source there are examples in there. The code you want will look like this:

public class PaymentMethodTypeResolver : ValueResolver<CustomerBillingTabView, PaymentMethodType>
{
    protected override PaymentMethodType ResolveCore(CustomerBillingTabView source)
    {

        string paymentMethod = source.Context.SourceValue as string;

        if (string.IsNullOrWhiteSpace(paymentMethod))
        {
            paymentMethod  = paymentMethod.Replace(" ", "");
            return source.New((PaymentMethodType)Enum.Parse(typeof(PaymentMethodType), paymentMethod, true));
        }

        return source.New(PaymentMethodType.Other);
    }
}