Question

我正在尝试使用dropdownList和两个外键，分别是modelId和categoryId。我正在使用带有selectList的ViewBag。

public ActionResult Create()
    {
        ViewBag.categoryId = new SelectList(db.Category, "categoryId", "name");
        ViewBag.modelId = new SelectList(db.Model, "modelId", "name");
        return View();
    } 

    //
    // POST: /Product/Create

    [HttpPost]
    public ActionResult Create(Product product)
    {
        if (ModelState.IsValid)
        {
            db.Product.Add(product);
            db.SaveChanges();
            return RedirectToAction("Index");  
        }
        ViewBag.categoryId = new SelectList(db.Category, "categoryId", "name", product.categoryId);
        ViewBag.modelId = new SelectList(db.Model, "modelId", "name", product.modelId);
        return View(product);
    }

这是我的Create.cshtml。

<div class="editor-label">
        @Html.LabelFor(model => model.Category)
    </div>
    <div class="editor-field">
        @Html.DropDownList("categoryId", "--Select--")
    </div>

    <div class="editor-label">
        @Html.LabelFor(model => model.Model)
    </div>

    <div class="editor-field">
        @Html.DropDownList("modelId", "--Select--")
    </div>

按下提交按钮的时候，出现错误， '已经添加了具有相同键的项目' 有什么问题？模型中有问题吗？

这是我的模特。

--Prodruct.cs--

public class Product
{
    [Key] public int productId { get; set; }

    [Required(ErrorMessage = "Please select category")]
    public int categoryId { get; set; }

    [Required(ErrorMessage = "Please select model")]
    public int modelId { get; set; }

    [DisplayName("Model name")]
    public String model { get; set; }

    public virtual Category Category { get; set; }
    public virtual Model Model { get; set; }
}

--Category.cs--
public class Category
{
    [Key] public int categoryId { get; set; }
    public String name { get; set; }
}

--Model.cs--
public class Model
{
    [Key] public int modelId { get; set; }
    public String name { get; set; }
}

--RentalDB.cs--
public class rentalDB : DbContext
{
    public DbSet<Product> Product { get; set; }
    public DbSet<Model> Model { get; set; }
    public DbSet<Customer> Customer { get; set; }
    public DbSet<Order> Order { get; set; }
    public DbSet<Cart> Cart { get; set; }
    public DbSet<Category> Category { get; set; }
    public DbSet<OrderDetails> OrderDetails { get; set; }

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        modelBuilder.Conventions.Remove<PluralizingTableNameConvention>();
    }
}

哪里错了？ “创建”中的索引页面可以获取类别数据和模型数据。但是，当我提交它时，它有错误，“已经添加了具有相同键的项目”。你能帮我解决问题吗？谢谢。

- 增加了更多编码 -

我正在使用这个LINQ。可能这里有问题。

如何在此处添加“模型”实体？

var product = from a in db.Product.Include(a => a.Category)
                      select a;

Answer 1

我就是这样做的。

我建议您不要将您的域模型发送到视图，而是为每个视图创建一个视图模型。这样做只会包含屏幕上的内容。

为您的创建视图创建新的视图模型：

public class ProductCreateViewModel
{
     // Include other properties if needed, these are just for demo purposes

     public string Name { get; set; }
     public string SKU { get; set; }
     public string LongDescription { get; set; }

     // This is the unique identifier of your category,
     // i.e. foreign key in your product table
     public int CategoryId { get; set; }
     // This is a list of all your categories populated from your category table
     public IEnumerable<Category> Categories { get; set; }

     // This is the unique identifier of your model,
     // i.e. foreign key in your product table
     public int ModelId { get; set; }
     // This is a list of all your models populated from your model table
     public IEnumerable<Model> Models { get; set; }
}

分类：

public class Category
{
     public int Id { get; set; }
     public string Name { get; set; }
}

模特课：

public class Model
{
     public int Id { get; set; }
     public string Name { get; set; }
}

在您的“创建”视图中，您将拥有以下内容：

@model MyProject.ViewModels.ProductCreateViewModel

@using (Html.BeginForm())
{
     <table>
          <tr>
               <td><b>Category:</b></td>
               <td>
                    @Html.DropDownListFor(x => x.CategoryId,
                         new SelectList(Model.Categories, "Id", "Name", Model.CategoryId),
                         "-- Select --"
                    )
                    @Html.ValidationMessageFor(x => x.CategoryId)
               </td>
          </tr>
          <tr>
               <td><b>Model:</b></td>
               <td>
                    @Html.DropDownListFor(x => x.ModelId,
                         new SelectList(Model.Models, "Id", "Name", Model.ModelId),
                         "-- Select --"
                    )
                    @Html.ValidationMessageFor(x => x.ModelId)
               </td>
          </tr>
     </table>

     <!-- Add other HTML controls if required and your submit button -->
}

您的创建操作方法：

public ActionResult Create()
{
     ProductCreateViewModel viewModel = new ProductCreateViewModel
     {
          // Here you do database calls to populate your dropdowns
          Categories = categoryService.GetAllCategories(),
          Models = modelService.GetAllModels()
     };

     return View(viewModel);
}

[HttpPost]
public ActionResult Create(ProductCreateViewModel viewModel)
{
     // Check that viewModel is not null

     if (!ModelState.IsValid)
     {
          viewModel.Categories = categoryService.GetAllCategories();
          viewModel.Models = modelService.GetAllModels();

          return View(viewModel);
     }

     // Mapping
     Product product = ...  // Do your mapping here

     // Insert product in database
     productService.Insert(product);

     // Return the view where you need to be
}

我还建议您使用AutoMapper在域模型和视图模型之间为您进行映射。我还建议您查看Fluent Validation以处理您的视图模型验证。

我希望这会有所帮助。

更新的答案

用于获取所有类别的服务可能如下所示：

public class CategoryService : ICategoryService
{
     private readonly ICategoryRepository categoryRepository;

     public CategoryService(ICategoryRepository categoryRepository)
     {
          // Check if category repository is not null, throw exception if it is

          this.categoryRepository = categoryRepository;
     }

     public IEnumerable<Category> GetAllCategories()
     {
          return categoryRepository.GetAllCategories();
     }
}

categoryRepository由Autofac注入。

类别服务界面：

public interface ICategoryService
{
     IEnumerable<Category> GetAllCategories();
}

我目前仍然使用Entity Framework 4.1代码。

我的类别存储库：

public class CategoryRepository : ICategoryRepository
{
     MyContext db = new MyContext();

     public IEnumerable<Category> GetAllCategories()
     {
          return db.Categories
               .OrderBy(x => x.Name);
     }
}

我的类别存储库界面：

public interface ICategoryRepository
{
     IEnumerable<Category> GetAllCategories()
}

Answer 2

public class Test
{
    rentalDB db = new rentalDB();
    public Product LoadProductById(int pId)
    {
        return db.Products.Include(p => p.Model).Include(p => p.Category).Where(p => p.productId == pId).SingleOrDefault();
    } // To get specific product.

    public IEnumerable<Product> LoadAllProducts()
    {
        return db.Products.Include(p => p.Model).Include(p => p.Category).ToList();
    } // To get all products.
}

我已将您的DbSet更改为产品使其更清晰。这是您加载一个产品或所有产品的所有引用的方式，以便迭代它们。

ViewBag多个SelectList用于下拉列表

2 个答案: