I have a problem mapping a property containing a custom list that inherits from IEnumerable
(if i remove that inheritance, this example works). I have simplified the problem into this model:
public interface IMyEnumerable<T> : IEnumerable<T> { }
public class MyIEnumerable<T> : IMyEnumerable<T>
{
private readonly IEnumerable<T> _items;
public MyIEnumerable(IEnumerable<T> items)
{
_items = items;
}
public IEnumerator<T> GetEnumerator()
{
return _items.GetEnumerator();
}
IEnumerator IEnumerable.GetEnumerator()
{
return GetEnumerator();
}
}
public class Source
{
public List<SourceItem> Items { get; set; }
}
public class Destination
{
public IMyEnumerable<DestinationItem> Items { get; set; }
}
public class SourceItem
{
public string Name { get; set; }
}
public class DestinationItem
{
public string Name { get; set; }
}
Then i try to use is this way:
public class MyResolver : ValueResolver<Source, IMyEnumerable<DestinationItem>>
{
protected override IMyEnumerable<DestinationItem> ResolveCore(Source source)
{
var destinationItems = Mapper.Map<List<SourceItem>, IEnumerable<DestinationItem>>(source.Items);
return new MyIEnumerable<DestinationItem>(destinationItems);
}
}
// Mappings
Mapper.CreateMap<Source, Destination>()
.ForMember(x => x.Items, m => m.ResolveUsing<MyResolver>());
Mapper.CreateMap<SourceItem, DestinationItem>();
// Using the mappings
var source = // not really relevant
var destination = Mapper.Map<Destination>(source);
This gives me the following exception (slightly edited for readability):
Mapping types:
MyIEnumerable`1 -> IMyEnumerable`1
MyIEnumerable`1[[DestinationItem]] -> IMyEnumerable`1[[DestinationItem]]
Destination path:
Destination.Items.Items
Source value:
MyIEnumerable`1[DestinationItem]
----> System.ArgumentException : Object of type System.Collections.Generic.List`1[DestinationItem] cannot be converted to type IMyEnumerable`1[DestinationItem].
Any idea how i can fix the mapping so that i can get this to work?
Assuming the following:
Then the following work:
Nothing else seems to work due to some combination of covariance and contravariance between
List<T>
,IEnumerable<T>
andIMyEnumerable<T>