Question

我的Asp.Net Mvc项目中有以下模型。创建新对象时，还会创建一个包含“选项”和“照片”的新列表，以便您只需向对象添加新的“选项和图片”。

public class VehicleModels
{
    [Key]
    public virtual int Id { get; set; }
    public virtual string Naam { get; set; }
    public virtual string Merk { get; set; }
    public virtual string Brandstof { get; set; }
    public virtual string Kleur { get; set; }
    public virtual string TypeVanMerk { get; set; }
    public virtual string TypeVanTransmissie { get; set; }
    public virtual int Kilometerstand { get; set; }
    public virtual int Bouwjaar { get; set; }
    public virtual int AantalDeuren { get; set; }
    public List<Optie> Options { get; set; }
    public List<Foto> Fotos { get; set; }

    public VehicleModels()
    {
        Options = new List<Optie>();
        Fotos = new List<Foto>();
    }  

}

我在控制器中有这个编辑

[HttpPost]
        [ValidateAntiForgeryToken]
        public ActionResult Edit(int? id, HttpPostedFileBase upload)
        {
            if (id == null)
            {
                return new HttpStatusCodeResult(HttpStatusCode.BadRequest);
            }
            var VehicleToUpdate = db.VehicleModels.Find(id);
            if (TryUpdateModel(VehicleToUpdate))
            {
                try
                {
                    if (upload != null && upload.ContentLength > 0)
                    {
                        if (VehicleToUpdate.Fotos.Any(f => f.VehicleModelsID == VehicleToUpdate.Id))
                        {
                            db.Fotos.Remove(VehicleToUpdate.Fotos.First(f => f.VehicleModelsID == VehicleToUpdate.Id));
                        }

                        var picture = new Foto
                        {
                            FotoNaam = System.IO.Path.GetFileName(upload.FileName),
                            ContentType = upload.ContentType
                        };
                        using (var reader = new System.IO.BinaryReader(upload.InputStream))
                        {
                            picture.Content = reader.ReadBytes(upload.ContentLength);
                        }
                        VehicleToUpdate.Fotos.Add(picture);
                    }
                    db.Entry(VehicleToUpdate).State = EntityState.Modified;
                    db.SaveChanges();

                    return RedirectToAction("Index");
                }
                catch (RetryLimitExceededException /* dex */)
                {
                    //Log the error (uncomment dex variable name and add a line here to write a log.
                    ModelState.AddModelError("", "Unable to save changes. Try again, and if the problem persists, see your system administrator.");
                }
            }
            return View(VehicleToUpdate);

        }

我的问题：

调试时我发现我的Edit方法中的这行代码（var VehicleToUpdate = db.VehicleModels.Find(id);）创建了一个新的模型对象，似乎将属性绑定到该新对象。但是因为它通过了构造函数，所以两个列表都被擦掉了。

当我尝试更改对象的图片时问题就出现了，因为列表是空的，它不会删除任何内容而且它也不会添加新图像，而只是再次添加旧图像，留下我与2x相同的图像。

我应该在其他地方实例化我的列表吗？如果是的话，哪里适当的地方？

旁注：我按照this教程将图像添加到项目中。

Answer 1

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如果他们没有填充并且变为空，那么请检查您的数据库。要么数据不存在。如果数据存在，则外键约束被破坏。检查并更正相同的内容。更正数据库后，请在项目中的Entity Framework的edmx文件中更新模型。之后，实体框架应适当填充数据，图像将更新，而不是添加副本。

在哪里实例化新列表<t>？

1 个答案: