Запрос к вложенному классу

public class Article
    {
        [Key]
        public int Id { get; set; }
        [Required]
        public string Title { get; set; }
        public string Text { get; set; }
        public string Author { get; set; }
      
        [Display(Name = "Организация")]
        public int OrgId { get; set; }
        [ForeignKey("OrgId")]
        public virtual Organisation Organisation { get; set; }
 
        public List<AttachmentArticle> Attachment { set; get; }
 
    }
    
     public class AttachmentArticle
    {
        [Key]
        public int Id { get; set; }
        public byte[] Content { get; set; }
    }

FileResult GetBytes(int? id){
        var articles = _db.Article.Find(id);
            articles.Attachment = new List<AttachmentArticle>() { new AttachmentArticle() }
            ........}

@model Contacts.Models.Article

AttachmentArticle.Content

public FileResult GetBytes(int? id)
        {
            var articles = _db.Article.Include(i => i.Attachment).Where(i => i.Id == id).FirstOrDefault();
            byte[] mas = articles.Attachment.FirstOrDefault().Content;
            string file_type = "application/doc";
            string file_name = "doc.doc";
            return File(mas, file_type, file_name);
        }

 byte[] mas = articles.Attachment.FirstOrDefault().Content