AutoMapper mapping objects in source child list to existing objects in destination child entity collection

Question

I have the following situation:

public class Parent : EntityObject
{
    EntityCollection<Child> Children { get; set; }
}

public class Child : EntityObject
{
    int Id { get; set; }
    string Value1 { get; set; }
    string Value2 { get; set; }
}

public class ParentViewModel
{
    List<ChildViewModel> Children { get; set; }
}

public class ChildViewModel
{
    int Id { get; set; }
    string Value1 { get; set; }
    string Value2 { get; set; }
}

Mapper.CreateMap<ParentViewModel, Parent>();

Mapper.CreateMap<ChildViewModel, Child>();

Is it possible to get AutoMapper to:

• Map objects in the ParentViewModel.Children list to objects in the Parent.Children EntityCollection with matching Ids.
• Create new objects in Parent.Children for objects in ParentViewModel.Children where an object with the id from source is not found in the destination list.
• Remove objects from Parent.Children where the destination id does not exist in the source list.

Am I going about this all wrong?

Answer 1

I'm afraid automapper is not meant to be used for mapping to a populated object, it will erase the Parent.Children wen you invoke Map(). You have several approaches here:

• Create the condition to execute the map on children youself:

   foreach (var childviewmodel in parentviewmodel.Children)
   {
       if (!parent.Children.Select(c => c.Id).Contains(childviewmodel.Id))
       {
           parent.Children.Add(Mapper.Map<Child>(childviewmodel));
       }
   }
  

Add more if()s for other behaviour

• Create an IMappingAction and hook it in the BeforeMap method:

   class PreventOverridingOnSameIds : IMappingAction<ParentViewModel, Parent>
   {
       public void Process (ParentViewModel source, Parent destination)
       {
           var matching_ids = source.Children.Select(c => c.Id).Intersect(destination.Children.Select(d => d.Id));
           foreach (var id in matching_ids)
           {
               source.Children = source.Children.Where(c => c.Id != id).ToList();
           }
       }
   }
  

..and later on

    Mapper.CreateMap<ParentViewModel, Parent>()
        .BeforeMap<PreventOverridingOnSameIds>();

this way you let automapper do the job.