Asp.net mvc 如何在编辑具有空值的条目时从DB获取值

错误消息： ObjectStateManager中已存在具有相同密钥的对象。ObjectStateManager无法跟踪具有相同密钥的多个对象

如果fileupload有空值（不更改），我想从数据库中获取图像Url。 我的意思是，如果我改变了smallImage而没有改变LargeImage，那么它应该从DB中得到LargeImage值

[HttpPost]
    public ActionResult Edit(Blog blog, HttpPostedFileBase smallImage, HttpPostedFileBase largeImage)
    {
        if (ModelState.IsValid)
        {
            if (smallImage != null)
            {
                blog.SmallImage = smallImage.ContentLength + "_" + smallImage.FileName;
                string filepath = Path.Combine(Server.MapPath("~/Content/Blog/"), smallImage.ContentLength + "_" + smallImage.FileName);
                smallImage.SaveAs(filepath);
            }
            else
            {
                blog.SmallImage = db.Blogs.Find(blog.ID).SmallImage;
            }
            if (largeImage != null)
            {
                blog.LargeImage = largeImage.ContentLength + "_" + largeImage.FileName;
                string filepath = Path.Combine(Server.MapPath("~/Content/Blog/"), largeImage.ContentLength + "_" + largeImage.FileName);
                largeImage.SaveAs(filepath);
            }
            else
            {
                blog.LargeImage = db.Blogs.Find(blog.ID).LargeImage;
            }
            blog.PostDate = Convert.ToDateTime(DateTime.Now.ToShortDateString());
            db.Entry(blog).State = EntityState.Modified;
            db.SaveChanges();
            return RedirectToAction("Index");
        }
        return View(blog);
    }

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谢谢。

看起来这里的问题是，您两次加载同一个博客

改为加载一次，如下所示：

Blog existingBlog = db.Blogs.Find(blog.ID);
if (smallImage != null)
            {
                blog.SmallImage = smallImage.ContentLength + 
                                        "_" + smallImage.FileName;
                string filepath = Path.Combine(Server.MapPath("~/Content/Blog/"),
                           smallImage.ContentLength + "_" + smallImage.FileName);
                smallImage.SaveAs(filepath);
            }
            else
            {
                blog.SmallImage = existingBlog.SmallImage;
            }
            if (largeImage != null)
            {
                blog.LargeImage = largeImage.ContentLength + "_" +
                                     largeImage.FileName;
                string filepath = Path.Combine(Server.MapPath("~/Content/Blog/"),
                                                 largeImage.ContentLength + "_" +
                                                 largeImage.FileName);
                largeImage.SaveAs(filepath);
            }
            else
            {
                blog.LargeImage = existingBlog.LargeImage;
            }

---

你们都在加载博客的副本

 db.Blogs.Find(blog.ID)

以及将具有相同id的另一个附加到上下文

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

这意味着你在上下文中有两个相同的博客副本（不允许）

我建议用viewmodel替换回发的，比如

public ActionResult Edit(BlogViewModel viewModel, HttpPostedFileBase smallImage, HttpPostedFileBase largeImage)
{
    if (!ModelState.IsValid)
    {
        return View(viewModel);
    }
        var blog =  db.Blogs.Find(viewModel.ID);
        if (smallImage != null)
        {
            blog.SmallImage = smallImage.ContentLength + "_" + smallImage.FileName;
            string filepath = Path.Combine(Server.MapPath("~/Content/Blog/"), smallImage.ContentLength + "_" + smallImage.FileName);
            smallImage.SaveAs(filepath);
        }

        if (largeImage != null)
        {
            blog.LargeImage = largeImage.ContentLength + "_" + largeImage.FileName;
            string filepath = Path.Combine(Server.MapPath("~/Content/Blog/"), largeImage.ContentLength + "_" + largeImage.FileName);
            largeImage.SaveAs(filepath);
        }


        blog.Title = viewModel.Title;
        blog.Body = viewModel.Body; //etc

        db.SaveChanges();
        return RedirectToAction("Index");
}

---

您正在使用实体框架吗？