Dynamically mapping with Automapper

Question

I'm trying to conditionally map two objects based on ExtendedField.type. So if the type is textbox then I would map to the TextBox class, but if it's checkbox then I would map to Checkbox class. And of course this needs to be open for extension to map to other IHtmlElement derived types.

Mapper.Map<IEnumerable<ExtendedField, IEnumerable<IHtmlElement>>(extendedFields);

A sample of the objects:

public class ExtendedField {
    public string type { get; set; }
    public string prompt { get; set; }
    public string value { get; set; }
}

public Interface IHtmlElement {
    string label { get; set; }
    string type { get; set; }
    string value { get; set; }
}

public class TextBox : IHtmlElement {
    public string label { get; set; }
    public string type { get { return "textbox"; } }
    public string value { get; set; }
}

public class CheckBox : IHtmlElement {
    public string label { get; set; }
    public string type { get { return "checkbox"; } }
    public string value { get; set; }
}

I have created the mapping to map to IHtmlElement but I can't think of how to dynamically tell AutoMapper which concrete class to map to based off the type property.

Mapper.CreateMap<ExtendedField, IHtmlElement>()
      .ForMember(dest => dest.label, opt => opt.MapFrom(src => src.prompt))
      .ForMember(dest => dest.type, opt => opt.MapFrom(src => src.type))
      .ForMember(dest => dest.value, opt => opt.MapFrom(src => src.extendedFieldValue));

alxndr · Accepted Answer · 2013-09-26 23:40:32Z

2

in ExtendedField.type you must contain full qualified type name. write type converter:

public class ExtFieldToIHtmlElementConverter : TypeConverter<ExtendedField, IHtmlElement>
    {
        protected override IHtmlElement ConvertCore(ExtendedField source)
        {
            var obj = Activator.CreateInstance(Type.GetType(source.type)) as IHtmlElement;
            obj.label = source.prompt;
            obj.value = source.value;

            return obj;
        }
    }

mapping:

mapper.CreateMap<ExtendedField, IHtmlElement>().ConvertUsing<ExtFieldToIHtmlElementConverter>();

example of using:

var element = Mapper.Map<IHtmlElement>(extFieldObj); // become instance that implement IHtmlElement interface.

edited Sep 26, 2013 at 23:40

answered Sep 26, 2013 at 19:29

alxndr

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3 Comments

bflemi3 Over a year ago

Thank you, I really like this idea but I don't have the freedom to change ExtendedField.type value to be the fully qualified name of the class to be mapped to.

alxndr Over a year ago

mb you can create helper, that will contains private dictionary with string like "textbox", "checkbox" etc. as a key, and concrete type as a value and public method that become string as param and return necessary type for mapping. make some changes in ExtFieldToIHtmlElementConverter. see example here: pastebin.com/8neMdXhb

bflemi3 Over a year ago

yep, that's exactly the impl I was thinking of :)

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