Question

我尝试更新我的Products表但我不能因为抛出错误。

这是我的硬编码控制器：

[HttpPost]
public ActionResult EditProduct(ProductsViewModel productViewModel)
{
    TechStoreEntities context = new TechStoreEntities();

    Product newProduct = new Product
    {
        ProductId = productViewModel.ProductId,
        Name = productViewModel.Name,
        Price = productViewModel.Price,
        Discount = productViewModel.Discount,
        Quantity = productViewModel.Quantity,
        Size = productViewModel.Size,
        Description = productViewModel.Description,
        ProducerName = productViewModel.ProducerName,
        PaymentMethods = productViewModel.PaymentMethods,
        CategoryID = productViewModel.CategoryID,
        SubcategoryID = productViewModel.SubcategoryID,
        IsNew = productViewModel.IsNew,
        IsEnable = productViewModel.IsEnable
    };

    context.Entry(newProduct).State = EntityState.Modified;
    context.SaveChanges();

    ViewBag.CategoryID = new SelectList(context.Categories.Where(c => c.SubCategoryID == null), "CategoryID", "Name");
    ViewBag.SubcategoryID = new SelectList(context.Categories.Where(c => c.SubCategoryID != null), "CategoryID", "Name");

    return RedirectToAction("Products");
}

这是一个模型：

public class ProductsViewModel
{
    public int ProductId { get; set; }
    public string Name { get; set; }
    public int Price { get; set; }
    public int Discount { get; set; }
    public int Quantity { get; set; }
    public string Size { get; set; }
    public string Description { get; set; }
    public string ProducerName { get; set; }
    public string PaymentMethods { get; set; }
    public bool IsNew { get; set; }
    public bool IsEnable { get; set; }
    public string Category { get; set; }
    public int CategoryID { get; set; }
    public string Subcategory { get; set; }
    public int SubcategoryID { get; set; }
    public DateTime? CreateDate { get; set; }
}

我使用强类型视图：

@model MyTechStore.Models.ProductsViewModel

我添加了一个视图：

@Html.HiddenFor(model => model.ProductId)

当我启动应用程序并输入一些数据来更新现有数据并按保存时，抛出异常：

System.Data.Entity.Infrastructure.DbUpdateConcurrencyException

当我调试时，我看到只有ProductId为0.其他一切都没问题。我用脚手架控制器测试但是没关系。我想使用视图模型，而不是脚手架控制器使用我的数据库中的模型。

有人可以告诉我哪里错了吗？

我的GET方法：

public ActionResult EditProduct(int? id)
{
    TechStoreEntities context = new TechStoreEntities();

    ProductsManipulate product = new ProductsManipulate();

    ProductsViewModel editProduct = product.EditProduct(id);

    ViewBag.CategoryID = new SelectList(context.Categories.Where(c => c.SubCategoryID == null), "CategoryID", "Name");
    ViewBag.SubcategoryID = new SelectList(context.Categories.Where(c => c.SubCategoryID != null), "CategoryID", "Name");
    return View(editProduct);
}

我的数据访问层：

public ProductsViewModel EditProduct(int? id)
{
    TechStoreEntities context = new TechStoreEntities();
    Product dbProduct = context.Products.Find(id);
    ProductsViewModel product new ProductsViewModel
    {
        Name = dbProduct.Name,
        Price = dbProduct.Price,
        Quantity = dbProduct.Quantity,
        CategoryID = dbProduct.CategoryID,
        SubcategoryID = dbProduct.SubcategoryID,
        IsNew = dbProduct.IsNew
    };
    return product;
}

Answer 1

您需要在ProductId

中填充ProductsViewModel

public ProductsViewModel EditProduct(int? id)
{
    TechStoreEntities context = new TechStoreEntities();

    Product dbProduct = context.Products.Find(id);

    ProductsViewModel product = new ProductsViewModel()
    {
        // You need this line to pass the value to View
        ProductId = dbProduct.ProductId,

        Name = dbProduct.Name,
        Price = dbProduct.Price,
        Quantity = dbProduct.Quantity,
        CategoryID = dbProduct.CategoryID,
        SubcategoryID = dbProduct.SubcategoryID,
        IsNew = dbProduct.IsNew
    };

    return product;
}

Answer 2

该错误说的是，EF试图用这些字段更新Product，但它返回0 RowCount，因此它知道出现了问题。

正如您之前提到的，ProductId是0，这意味着您可能没有带有该ID的Product，因此当EF尝试更新它时，行count为0，这会导致EF抛出DbUpdateConcurrencyException。

如果您想要更新现有产品，则需要确保填充了您的ID。

否则，如果您需要upsert（更新或插入），首先需要检查给定ProductId是否存在记录，如果存在，请更新，否则执行插入。

存储更新，插入或删除语句影响了意外的行数（0）

2 个答案: