Use an enum to select which class to instantiate

Question

I have an enum that I am trying to associate to dto's:

 public enum DtoSelection
 {
     dto1,
     dto2,
     dto3,
 }

There are 108 and values in this enum.

I have a dto object for each of these dto's:

 public class dto1 : AbstractDto
 {
       public int Id { get; set; }
       //some stuff specific to this dto
 }

I am trying to make a method (eventually a service) that will return me a new dto object of the type associated to the the dto in question:

 private AbstractDto(int id)
 {
      if (id == DtoSelection.Dto1.ToInt()) //extension method I wrote for enums
            return new Dto1();
      if (id == DtoSelection.Dto2.ToInt())
            return new Dto2();
 }

Obviously I do not want to do this 108 times. For whatever reason my brain is just missing something obvious. What is the best way to handle this.

Answer 1

This class will do what you want as long as the Dto classes are defined in the same namespace as AbstractDto (you'll need to tweak it if not):

Given the following enums and classes:

public enum DtoSelection
{
    Dto1,
    Dto2,
    Dto3,
}

public abstract class AbstractDto
{
}

public class Dto1 : AbstractDto
{
}

public class Dto2 : AbstractDto
{
}

public class Dto3 : AbstractDto
{
}

This method will resolve them:

public static class DtoFactory
{
    public static AbstractDto Create(DtoSelection dtoSelection)
    {
        var type = Type.GetType(typeof(AbstractDto).Namespace + "." + dtoSelection.ToString(), throwOnError: false);

        if (type == null)
        {
            throw new InvalidOperationException(dtoSelection.ToString() + " is not a known dto type");
        }

        if (!typeof(AbstractDto).IsAssignableFrom(type))
        {
            throw new InvalidOperationException(type.Name + " does not inherit from AbstractDto");
        }

        return (AbstractDto)Activator.CreateInstance(type);
    }
}