How to avoid error regarding 1:0..1 in Entity Framework??

Question

Database

Hello, my task is that I pull the image path from the database and display it on the page, the image itself is stored in the file system. Here is my model 1:0..1

public class Album
    {

      
        public string Title { get; set; }
        public virtual Genre Genre { get; set; }

        public virtual ICollection<FileDetail> FileDetails { get; set; }
       
        [Key]
        public int AlbumId { get; set; }
        [DisplayName("Genre")]
        public int GenreId { get; set; }
        [DisplayName("Artist")]
        public int  ArtistId { get; set; }


        public decimal Price { get; set; }

        [DisplayName("Album Art URL")]
        [StringLength(1024)]
        public string AlbumArtUrl { get; set; }

        public virtual Artist Artist { get; set; }

        public virtual  MainFileDetails MainFileDetails { get; set; }

    }
}
 public class MainFileDetails
    {
        

        public Guid Id { get; set; }
        public string FileName { get; set; }
        public string Extension { get; set; }
        [Key, ForeignKey("Album")]

        public int AlbumId { get; set; }

       
        public virtual Album Album { get; set; }


    }
}

And here is the Edit method where we can upload a new photo:

[HttpPost]
        [ValidateAntiForgeryToken]
        public ActionResult Edit([Bind(Include = "AlbumId,Title,GenreId,ArtistId,Price,AlbumArtUrl")] Album album)
        {
            if (ModelState.IsValid)
            {
                //New Files
                for (int i = 0; i < Request.Files.Count; i++)
                {
                    var file = Request.Files[i];

                    if (file != null && file.ContentLength > 0)
                    {
                        var fileName = Path.GetFileName(file.FileName);
                        MainFileDetails fileDetail = new MainFileDetails()
                        {
                            FileName = fileName,
                            Extension = Path.GetExtension(fileName),
                            Id = Guid.NewGuid(),
                            AlbumId = album.AlbumId
                        };
                        var path = Path.Combine(Server.MapPath("~/Upload/"), fileDetail.Id + fileDetail.Extension);
                        file.SaveAs(path);


                        db.Entry(fileDetail).State = EntityState.Modified;


                    }
                }

                db.Entry(album).State = EntityState.Modified;
                db.SaveChanges();
                return RedirectToAction("Index");
            }
            ViewBag.ArtistId = new SelectList(db.Artists, "ArtistId", "Name", album.ArtistId);
            ViewBag.GenreId = new SelectList(db.Genres, "GenreId", "Name", album.GenreId);
            ViewBag.AlbumId = new SelectList(db.MainFileDetails, "AlbumId", "FileName", album.AlbumId);
            return View(album);
        }

But there is a problem, the fact is that when I made this relationship 1: 0..1, then the data in the Albums table already existed, and if, for example, go to the Edit page, with a product whose Id does not exist in the MainFileDetails linking table, then we the program does not allow to go to the Edit page, because it throws an exception in the view: "object reference not set to an instance of an object", here:

<img src="~/Upload/@(Model.MainFileDetails.Id + Model.MainFileDetails.Extension)" width="240" height="240" />

If you create a new product, then a new record with an ID will be linked to the MainFileDetails table and there will be no excepption. And what then to do with already existing data? I have to manually add data to the MainFileDetails table so that there are no exceptions, well, I have a couple of records, but what if there were a million? What to do in such a situation? Thanks

Answer 1

Isn't it better to check before the place that causes the exception?