A buddy class is more or less the direction your code snippet is journeying, except your manually coded partial Person class would have an inner class, like:
[MetadataType(typeof(Person.Metadata))]
public partial class Person {
private sealed class MetaData {
[RegularExpression(...)]
public string Email { get; set; }
}
}
Or you could have your manually partial Person class and a separate Meta class like:
[MetadataType(typeof(PersonMetaData))]
public partial class Person { }
public class PersonMetaData {
[RegularExpression(...)]
public string Email;
}
These are workarounds and having a mapped Presentation class may be more suitable.