Automapper flatten from three levels to two levels - automapper

Question

I use automapper v. 9 and I need to transform a 3 levels structure to a 2 levels structure.
I already tried with the IncludeMembers option, but I can't achieve the result I want.
Here is my model classes (simplified)
public partial class Mail
{
public Mail()
{
Mail_Files = new HashSet<Mail_Files>();
}
[Key]
public int Id { get; set; }
public string Oggetto { get; set; }
public string Testo { get; set; }
[InverseProperty("IdMailNavigation")]
public virtual ICollection<Mail_Files> Mail_Files { get; set; }
}
public partial class Mail_Files
{
[Key]
public int Id { get; set; }
public int IdMail { get; set; }
public int IdFile { get; set; }
[ForeignKey(nameof(IdFile))]
[InverseProperty(nameof(Files.Mail_Files))]
public virtual Files IdFileNavigation { get; set; }
[ForeignKey(nameof(IdMail))]
[InverseProperty(nameof(Mail.Mail_Files))]
public virtual Mail IdMailNavigation { get; set; }
}
public partial class Files
{
public Files()
{
Mail_Files = new HashSet<Mail_Files>();
}
[Key]
public int Id { get; set; }
public int IdTipoFile { get; set; }
public string FileName { get; set; }
public int? FileSize { get; set; }
[InverseProperty("IdFileNavigation")]
public virtual ICollection<Mail_Files> Mail_Files { get; set; }
}
I have to flatten this object to this:
public class MailFileResource
{
public int Id { get; set; }
public string FileName { get; set; }
}
public class MailResource
{
public int Id { get; set; }
public string Testo { get; set; }
public IEnumerable<MailFileResource> Files { get; set; }
}

Answer 1

I do it this way:
CreateMap<Files, MailFileResource>()
.ForMember(d => d.FileName, opt => opt.MapFrom(s => s.FileName))
.ForMember(d => d.Id, opt => opt.MapFrom(s => s.Id));
CreateMap<Mail_Files, MailFileResource>().IncludeMembers(s => s.IdFileNavigation);
CreateMap<Mail, MailResource>()
.ForMember(d => d.Files , opt => opt.MapFrom(s => s.Mail_Files))
.ForMember(d => d.Protezione, opt => opt.MapFrom(s => s.Protezione));
My mistake was to use IncludeMembers in Mail -> MailResource mapping too