Question

I want to make a cloning or mapping function where I can specify (once) which properties to copy to the target object.

The whole point here was a usage that looks something like this
(inspired by using GroupBy),

var botchedOrder = db.BuildingOrders.Find(id);
var redo = db.BuildingOrders.Create();
botchedOrder.MapTo(redo, x => new { x.BasePrice, x.FileAttachments, x.Notes });

This is over my head, but I was guessing at something like this,

public static void MapTo<TObject, TProps>(
    this TObject source,
    TObject target,
    Action<TProps> properties) //?
{
    //copy the defined properties from source to target somehow?
    //originally I thought I could make an array of delegates..
}

If this works then I can more easily handle different sets of properties in different ways when I am explicitly cloning or mapping objects. I’d like to stick w/ .NET to do this.

EDIT: forgot to indicate void

Answer 1

I’d recommend looking at AutoMapper since it kind of solves same kinds of problems. Also, different ORM sources (like Massive, Petapoco etc.) all have some implementations (since they need to map data from a DB to an object).

Basically, it works either using reflection – to iterate over given fields/properties and set them to another object (also via refleciton). There are approaches to dynamic method generation using IL Generator or Expression Trees that wrap all the reflection code into one nice and fast method generated and compiled at runtime (thus giving performance boost).

Another way to do would be using dynamics or Dictionaries instead of anonymous class – that would remove “anonimity” problem and would just require to map specific keys on to properties – may be done with reflection again (using for example [MappingAttribute(“Key”)] for distinction – attribute is a fiction, just to give a general idea).