Mapping open generics is possible in Automapper, however I have come accros some issue trying to combine it with custom type converters.
The following
cfg.CreateMap(typeof(IEnumerable<>), typeof(MyCustomCollectionType<>))
.ConvertUsing(typeof(MyConverter));
with MyConverter looking like this:
class MyConverter : ITypeConverter<object, object>
{
public object Convert(object source, object destination, ResolutionContext context)
{
//... do conversion
}
}
does just throw an exception when the mapping is created:
'System.InvalidOperationException' in mscorlib.dll
Additional information: This operation is only valid on generic types.
How can I define a custom type converter for open generic types? What interface do I need to implement?
Converters for open generics need to be generic types. It would look something like:
public class MyConverter<TSource, TDest>
: ITypeConverter<IEnumerable<TSource>, MyCustomCollectionType<TDest>> {
public MyCustomCollectionType<TDest> Convert(
IEnumerable<TSource> source,
MyCustomCollectionType<TDest> dest,
ResolutionContext context) {
// you now have the known types of TSource and TDest
// you're probably creating the dest collection
dest = dest ?? new MyCustomCollectionType<TDest>();
// You're probably mapping the contents
foreach (var sourceItem in source) {
dest.Add(context.Mapper.Map<TSource, TDest>(sourceItem));
}
//then returning that collection
return dest;
}
}
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