Improve general factory-type patterns to more SOLID-oriented?

Question

I was wondering how best to write such code so that it uses more SOLID principles ...

public static T TransformXmlToEntity<T>(string xml) { if(typeof(T) == typeof(EntityA)) { return TransformXmlToEntityA(xml); } else if (typeof(T) == typeof(EntityB)) { return TransformXmlToEntityB(xml); } } private static T TransformXmlToEntityA(string xml) { var entityA = new EntityA(); //mapping occurs; sudo code entityA.Person = xml.element(Person).value; ... return entityA; } private static T TransformXmlToEntityB(string xml) { var entityB = new EntityB(); //mapping occurs; sudo code entityB.Product = xml.element(Product).value; ... return entityB; } 

This code just feels wrong. But I can’t figure out how to do it better.

Answer 1

How about a conversion card?

 private static Dictionary<Type, Func<string,object>> conversionMap = new Dictionary<Type, Func<string,object>> { {typeof(EntityA), TransformXmlToEntityA}, {typeof(EntityB), TransformXmlToEntityB}, // .... } public static T TransformXmlToEntity<T>(string xml) { return (T)conversionMap[typeof(T)](xml); } 

Answer 2

I would do something like this

 interface IXmlTransformer { string Transform(object entity); } class EntityAXmlTransformer : IXmlTransformer { string Transform(object entity) { /* implementation */ } } class EntityBXmlTransformer : IXmlTransformer { string Transform(object entity) { /* implementation */ } } // ideally an IoC container would do this - but here is a naive factory implementation class XmlTransformerFactory { private static readonly Dictionary<Type, IXmlTransformer> transformers = new Dictionary<Type, IXmlTransformer> { { typeof(EntityA), new EntityAXmlTransformer() }, { typeof(EntityB), new EntityBXmlTransformer() } } public IXmlTransformer Get<T>() // could be static { IXmlTransformer transformer; if (!transformers.TryGetValue(typeof(T), out transformer)) { return null; } return transformer; } } 

Then you can do:

 var factory = new XmlTransformerFactory(); var transformerA = factory.Get<EntityA>(); string xmlA = transformerA.Transform(entityAInstance); var transformerB = factory.Get<EntityB>(); string xmlB = transformerB.Transform(entityBInstance);