我如何ModelBind与MVC 3和Entity Framework code首先一个多一对多的关系？ [英] How do I ModelBind a many-to-many relationship with MVC 3 and Entity Framework Code First?

问题描述

我在同样的问题，在未来我的MVC 3应用程序。我有一个视图以创建一个新的产品，并且产品可以被分配到一个或多个类别。这里是我的EF code首先模型类：

I'm coming across the same problem in my MVC 3 applications. I've got a view to create an new product and that product can be assigned to one or more categories. Here are my EF Code First Model Classes:

public class Product 
{
    public int ProductID { get; set; }
    public string Name { get; set; }
    public virtual ICollection<Category> Categories { get; set; }
}

public class Category 
{
    public int CategoryID { get; set; }
    public string Name { get; set; }
    public virtual ICollection<Product> Products { get; set; }
}

所以，我创建了创建产品视图视图模型，包括产品和类别的列表：

So, I create a view model for the create product view and include the product and a list of the categories:

public class ProductEditViewModel
{
    public Product Product { get; set; }
    public List<SelectListItem> CategorySelections { get; set; }

    public ProductEditViewModel(Product product, List<Category> categories)
    {
        this.Product = product;
        CategorySelections = categories.Select(c => new SelectListItem()
        {
            Text = c.Name,
            Value = c.CategoryID.ToString(),
            Selected = (product != null ? product.Categories.Contains(c) : false)
        }).ToList();
    }
}

所以，我渲染为名称的输入和复选框为每个类别的列表的视图（名为Product.Categories）。当我得到的形式调回我要保存的产品，其相关的类别（或如的ModelState是无效的，重新显示与类别选择用户所做的完整视图）。

So, I render a view with an input for the name and a list of checkboxes for each category (named "Product.Categories"). When my form gets posted back I want to save the product with its associated categories (or if the ModelState is invalid, to redisplay the view with the category selections the user made intact).

[HttpPost]
public ActionResult Create(Product product)
{
    if (ModelState.IsValid)
    {
        db.Products.Add(product);
        db.SaveChanges();
        return RedirectToAction("Index");
    }

    return View(new ProductEditViewModel(product, db.Categories.ToList()));
}

当我这样做，并选择一个或多个类别的ModelState中是无效的，并将它与下面的验证错误返回编辑观点：

When i do that and select one or more categories, the ModelState is invalid and it returns the Edit view with the following validation error:

值为'25 2'是无效的。 // 25和2作为CategoryIDs

The value '25,2' is invalid. // 25 and 2 being the CategoryIDs

这是有道理的，我认为这不能结合25和2成实际类别对象，但有使用自定义的模型绑定器，让我来标识转化为分类，并将其附加到上下文的标准方式？

It makes sense to me that it can't bind 25 and 2 into actual category objects, but is there a standard way to use a custom ModelBinder that would allow me to translate IDs into Categories and attach them to the context?

推荐答案

感谢@Slauma，这让我在正确的轨道上。这是我的创建和编辑方法后，详细说明如何管理关系（编辑是有点棘手，因为它有添加不存在于数据库中，并删除已被删除的项目，并在数据库中确实存在项目）。我添加了一个SelectedCategories属性（整数列表）我ProductEditViewModel持有从形式的结果。

Thanks @Slauma, that got me on the right track. Here is my Create and Edit post methods that detail how to manage the relationships (the edit is a bit trickier, because it has to add items that don't exist in the database and delete items that have been removed and do exist in the database). I added a SelectedCategories property (List of ints) to my ProductEditViewModel to hold the result from the form.

[HttpPost]
public ActionResult Create(ProductEditViewModel)
{
    viewModel.Product.Categories = new List<Category>();

    foreach (var id in viewModel.SelectedCategories)
    {
        var category = new Category { CategoryID = id };
        db.Category.Attach(category);

        viewModel.Product.Categories.Add(category);
    }

    if (ModelState.IsValid)
    {
        db.Products.Add(viewModel.Product);
        db.SaveChanges();
        return RedirectToAction("Index");
    }

    return View(new ProductEditViewModel(viewModel.Product, GetCategories()));
}

有关编辑的方法，我不得不在数据库中查询当前的产品，然后比较，与视图模型。

For the Edit method I had to query the database for the current product and then compare that with the viewModel.

[HttpPost]
public ActionResult Edit(ProductEditViewModel viewModel)
{
    var product = db.Products.Find(viewModel.Product.ProductID);

    if (ModelState.IsValid)
    {
        UpdateModel<Product>(product, "Product");

        var keys = product.CategoryKeys; // Returns CategoryIDs

        // Add categories not already in database
        foreach (var id in viewModel.SelectedCategorys.Except(keys))
        {
            var category = new Category { CategoryID = id }; // Create a stub
            db.Categorys.Attach(category);

            product.Categories.Add(Category);
        }

        // Delete categories not in viewModel, but in database
        foreach (var id in keys.Except(viewModel.SelectedCategories))
        {
            var category = product.Categories.Where(c => c.CategoryID == id).Single();

            product.Categories.Remove(category);
        }

        db.SaveChanges();
        return RedirectToAction("Index");
    }
    else
    {
        // Update viewModel categories so it keeps users selections
        foreach (var id in viewModel.SelectedCategories)
        {
            var category = new Category { CategoryID = id }; // Create a stub
            db.Categories.Attach(category);

            viewModel.Product.Categories.Add(category);
        }
    }

    return View(new ProductEditViewModel(viewModel.Product, GetCategories()));
}

这是更code，我希望它会是这样，但它实际上是pretty高效利用存根，只添加/删除了什么变化。

It is more code that I was hoping it would be, but it is actually pretty efficient with using the stubs and only adding/deleting what has changed.

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