Question

美好的一天，我是ASP.NET的新手，我无法弄清楚为什么我的代码不起作用。我有模特：

using System.ComponentModel.DataAnnotations;
using System.Drawing;
using System.Globalization;

namespace WebApp.Models
{
public class News
{
    public int NewsId { get; set; }
    public string title { get; set; }
    public string description { get; set; }
    public virtual Picture picture { get; set; }
    public int guid { get; set; }
}

public class Picture
{
    public int PictureId { get; set; }
    public byte[] image { get; set; }
    public int width { get; set; }
    public int height { get; set; }
    public int hash { get; set; }
}
}

我正在努力创造新的＆＃34;新闻＆＃34;通过邮寄表格：

    // POST: News/Create
    // To protect from overposting attacks, please enable the specific properties you want to bind to, for 
    // more details see http://go.microsoft.com/fwlink/?LinkId=317598.
    [HttpPost]
    [ValidateAntiForgeryToken]
    public ActionResult Create(News news, HttpPostedFileBase uploadImage)
    {
        if (ModelState.IsValid && uploadImage != null)
        {
            byte[] imageData = null;
            using (var binaryReader = new BinaryReader(uploadImage.InputStream))
            {
                imageData = binaryReader.ReadBytes(uploadImage.ContentLength);
            }
            news.picture = new Picture()
            {
                hash = 0,
                image = imageData,
                width = 0,
                height = 0
            };
            db.News.Add(news);
            db.SaveChanges();
            return RedirectToAction("Index");
        }
        return View(news);
    }

但是当我从db检索数据时，我得到空指针异常：当我打电话给调试器时，我发现了＆＃34; news.picture＆＃34; value为null。但在db.SaveChanges（）之前它100％不为null。看起来我正在做一些愚蠢的错误，但是我找不到那些遇到这个问题的人。 THX。

Answer 1

尝试以下

[HttpPost]
    [ValidateAntiForgeryToken]
    public ActionResult Create(News news, HttpPostedFileBase uploadImage)
    {
        if (ModelState.IsValid && uploadImage != null)
        {
            byte[] imageData = null;
            using (var binaryReader = new BinaryReader(uploadImage.InputStream))
            {
                imageData = binaryReader.ReadBytes(uploadImage.ContentLength);
            }
            var picture = new Picture()
            {
                hash = 0,
                image = imageData,
                width = 0,
                height = 0
            };
            db.Pictures.Add(picture); // make sure that the picture was tracked by the EF
            news.picture = picture;
            db.News.Add(news);
            db.SaveChanges();
            return RedirectToAction("Index");
        }
        return View(news);
    }

Answer 2

我会做出以下更改，看看是否有帮助。

namespace WebApp.Models
{
  public class News
  {
      public int Id { get; set; }
      public string Title { get; set; }
      public string Description { get; set; }

      [ForeignKey("Picture")]
      public int PictureId { get; set; }
      public virtual Picture Picture { get; set; }

      // not sure why this is here
      public int guid { get; set; }
  }

  public class Picture
  {
      public int Id { get; set; }

      public byte[] ImageData { get; set; }
      public string ContentType { get; set; }

      public int width { get; set; }
      public int height { get; set; }
      public int hash { get; set; }
  }
}

控制器：

// POST: News/Create
// To protect from overposting attacks, please enable the specific properties you want to bind to, for 
// more details see http://go.microsoft.com/fwlink/?LinkId=317598.
[HttpPost]
[ValidateAntiForgeryToken]
public ActionResult Create(NewsDto news, HttpPostedFileBase uploadImage)
{
    if (ModelState.IsValid && uploadImage != null)
    {
        var imageData = byte[uploadImage.ContentLength];
        using (var binaryReader = new BinaryReader(uploadImage.InputStream))
        {
            imageData = binaryReader.ReadBytes(uploadImage.ContentLength);
        }

        var newsEntity = new New {
          Title = news.Title,
          Description = news.Description,
          Picture = new Picture()
          {
              ImageData = imageData,
              ContentType = contentType // I would get that from the HttpPostedFileBase
          }
        }

        // I always wrap my database connections in a using.
        using (var db = new DbContext()) {
          db.News.Add(newsEntity);
          db.SaveChanges();
        }

        return RedirectToAction("Index");
    }
    return View(news);
}

Answer 3

我不知道为什么，但是当我添加虚拟财产时，所有工作都有效：

public virtual Picture picture { get; set; }

ASP.NET保存复杂的实体模型

3 个答案: