Using ValueInjecter, is there a way to only inject a given property one time

Question

Given 3 classes,

A, and B which each have an ID property, and then various other properties

and C, which has an ID, and the combined properties of A and B,

I want to

C.InjectFrom(A);
C.InjectFrom(B);

such that the ID from A is preserved and not overwritten by B.

Obviously in this simple case, I could just reverse the order of the two calls, but in my real world example, it is slightly more complicated where I cannot just solve the problem with ordering.

Esentially I want the second injection to ignore anything that the first injection has already handled, and this may be continued down a chain of several injections. Some of these injections may be from the same objects too

C.InjectFrom(A);
C.InjectFrom<SomeInjector>(A);
C.InjectFrom<SomeInjector2>(A);
C.InjectFrom<SomeInjector3>(A);

etc.

Answer 1

here you go:

using System;
using System.Collections.Generic;
using Omu.ValueInjecter;

namespace ConsoleApplication2
{
    class Program
    {
        static void Main(string[] args)
        {

            var a = new { Id = 1, P1 = "p1" };
            var b = new { Id = 2, P2 = "p2" };

            var c = new C();

            var propList = new List<string>();
            c.InjectFrom(new HandlePropOnce(propList), a);
            c.InjectFrom(new HandlePropOnce(propList), b);

            Console.WriteLine("Id = {0} P1 = {1} P2 = {2}", c.Id, c.P1, c.P2);
        }
    }

    public class C
    {
        public int Id { get; set; }

        public string P1 { get; set; }

        public string P2 { get; set; }
    }

    public class HandlePropOnce : ConventionInjection
    {
        private readonly IList<string> handledProps;

        public HandlePropOnce(IList<string> handledProps)
        {
            this.handledProps = handledProps;
        }

        protected override bool Match(ConventionInfo c)
        {
            if (handledProps.Contains(c.SourceProp.Name)) return false;

            var isMatch = c.SourceProp.Name == c.TargetProp.Name && c.SourceProp.Type == c.TargetProp.Type;

            if (isMatch) handledProps.Add(c.SourceProp.Name);
            return isMatch;
        }
    }
}