Validation of nested collections about wcfdataannotations HOT 2 CLOSED

[DataContract(IsReference = true)]
public class MyDto : MyBase
{
   [DataMember]
   [Required]
   public string OrderNo { get; set; }
   
   [DataMember]
   public ICollection<MySubDto> MySubDtoCollection { get; set; } = new  List<MySubDto>();
}

And my subcollection class:

[DataContract(IsReference = true)]
public class MySubDto : IValidatableObject
{
    [DataMember]
    [Required]
    public string IssueNo { get; set; }

    public IEnumerable<ValidationResult> Validate(ValidationContext validationContext)
    {
        throw new NotImplementedException();
    }
}