AutoMapper custom TypeConverter not working

Question

I'm trying to integrate AutoMapper into my project and it's mostly working out, now that I know how to project EntityFramework objects , but I keep getting this exception: Unable to create a map expression from System.Byte to System.Int32 . So, I figure I'll make a custom type converter and it will work, except it doesn't:

public sealed class ByteToInt32Converter : TypeConverter<byte, int> {
    protected override int ConvertCore(
        byte source) {
        return (int)source;
    }
}

Mapper.CreateMap<byte, int>().ConvertUsing<ByteToInt32Converter>();

Looking at the documentation and other search results, this should be correct, but I'm still getting an exception. What do?

Update

Per Scott's request, here's my source object, Company , and the destination object SelectItem :

public partial class Company {
    public byte Id { get; set; }
    public string Name { get; set; }

    #region Relationship Properties
    public byte? ParentCompanyId { get; set; }

    public virtual ICollection<Company> Companies { get; private set; }
    public virtual ICollection<Employee> Employees { get; private set; }
    public virtual Company ParentCompany { get; set; }
    public virtual ICollection<State> States { get; private set; }
    #endregion

    public Company() {
        this.Companies = new List<Company>();
        this.Employees = new List<Employee>();
        this.States = new List<State>();
    }
}

public sealed class SelectItem : ISelectItem {
    public string Key { get; set; }
    public int Value { get; set; }
}

public interface ISelectItem : IItem {
    string Key { get; set; }
    int Value { get; set; }
}

public interface IItem {
}

And here's the mapping code:

Mapper.CreateMap<Company, SelectItem>()
    .ForMember(
        d => d.Key,
        o => o.MapFrom(
            s => s.Name))
    .ForMember(
        d => d.Value,
        o => o.MapFrom(
            s => s.Id));

I'm basically trying to flatten the Company object down to a "key-value pair" object that I can pass into the MVC Html.DropDownList() . I didn't particularly care to match the types of the Key Id since I was only using it to generate the drop down list so I just left it all as int . Granted, I could try to be generic, pass in the key type, etc, but it just feels way too complicated for not much gain.

Pretty much all of the objects I would want to use as drop down list options, follow the same convention.

Answer 1

Try this converter

 public class ByteToInt32Converter : ITypeConverter<byte, int>
    {
        public int Convert(ResolutionContext context)
        {
            return System.Convert.ToInt32(context.SourceValue);
        }
    }

Mapper.CreateMap<byte, int>().ConvertUsing<ByteToInt32Converter>();

// your Company to SelectItem mapping code.