不能在ASP.Net MVC 3项目，实体框架的SaveChanges [英] Can't SaveChanges with Entity Framework in ASP.Net MVC 3 project

问题描述

学习asp.net MVC 3 + EF code-第一。我是新来的两个。我的例子很简单，但我仍然不能使它发挥作用。失去了一些东西简单明了...

Studying asp.net mvc 3 + EF code-first. I am new to both. My example is trivial, but I still can't make it work. Missing something simple and obvious...

我有一个类：

 public class Product
 {
    [HiddenInput(DisplayValue = false)]
    public int ProductID { get; set; }

    [Required(ErrorMessage = "Please enter a product name")]
    public string Name { get; set; }

    [Required(ErrorMessage = "Please enter a description")]
    [DataType(DataType.MultilineText)]
    public string Description { get; set; }

    [Required]
    [Range(0.01, double.MaxValue, ErrorMessage = "Please enter a positive price")]
    public decimal Price { get; set; }

    [Required(ErrorMessage = "Please specify a category")]
    public string Category { get; set; }
}

和的DbContext ：

public class EFDbContext : DbContext
{
    public DbSet<Product> Products { get; set; }
}

和存储库：

public class EFProductRepository : IProductRepository
{
    private EFDbContext context = new EFDbContext();

    public IQueryable<Product> Products
    {
        get
        {
            return context.Products;
        }
    }

    public void SaveProduct(Product product)
    {
        if (product.ProductID == 0)
            context.Products.Add(product);

        context.SaveChanges();
    }
}

MVC的控制器：

The mvc controller:

public class AdminController : Controller
{
    private IProductRepository repository;

    public AdminController(IProductRepository repo)
    {
        repository = repo;
    }

    public ViewResult Index()
    {
        return View(repository.Products);
    }

    public ViewResult Edit(int productId)
    {
        Product product = repository.Products.FirstOrDefault(p => p.ProductID == productId);
        return View(product);
    }

    [HttpPost]
    public ActionResult Edit(Product product)
    {
        if (ModelState.IsValid)
        {
            repository.SaveProduct(product);
            TempData["message"] = string.Format("{0} has been saved", product.Name);
            return RedirectToAction("Index");
        }
        else
        {
            // there is something wrong with the data values
            return View(product);
        }
    }
}

它让我看到的产品列表中，打开编辑视图，验证一切按属性集...

It lets me see the list of products, opens the edit view, validates everything according to the set of attributes...

当我保存验证它进入HTTP POST 修改方法的变化并进行必要的的SaveChanges（）。

When I save validated changes it goes to the Http Post Edit method and makes the necessary SaveChanges().

它不抛出任何异常，它的推移和重定向我的产品清单。

It doesn't throw any exceptions, it goes on and redirect me to the list of products.

编辑的项目保持不变。

的基础数据库（在到的ConnectionStrings 连接的w​​eb.config ）保持不变为好。

The underlying database (connected through connectionstrings in web.config) stays unchanged as well.

推荐答案

您需要附加EF之外创建实体实例，让EF知道它已被修改。

You need to attach the entity instance created outside EF and let EF know that it has been modified.

public void SaveProduct(Product product)
{
    if (product.ProductID == 0)
    {
        context.Products.Add(product);
    }
    else
    {
        context.Products.Attach(product);
        context.Entry(product).State = EntityState.Modified;
    }

    context.SaveChanges();
}

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