AutoMapper: Merging values of items in a collection from one instance to another

Question

I am trying to figure out how to merge two complex object instances using AutoMapper. The parent object has a property which is a collection of child objects:

Answer 1

It's looking more and more likely that I will be unable to come up with mappings to handle this scenario; fair enough really as AutoMapper was never intended to be used to merge values in this way.

So I have resorted to handling the collection manually within a loop. For the purposes of this answer, I am assuming that Parent.A is uniquely identifying property:

Mapper.CreateMap()
    .ForMember(parent => parent.Children, opt => opt.Ignore());

Mapper.CreateMap()
    .ForMember(child => child.C, opt => opt.Ignore());

Mapper.Map(parentOne, parentTwo);

foreach (var childTwo in parentTwo.Children)
{
    var childOne = parentOne.Children.Where(child => child.A == childTwo.A).Single();
    Mapper.Map(childOne, childTwo);
}