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:

• One is to create yourself the condition to execute the map on childrens:

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

  Other ifs for other behaviour

• One is to 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.