Question

我有一个简单的应用程序，它应该显示列表的元素，但它在调试时返回一个空数组。我需要这些元素以动态显示。我想知道程序是否因为以下代码而无法正常工作......

StoreController.cs

using GetMed.Models;

namespace GetMed.Controllers
{
    public class StoreController : Controller
    {
        GetMedEntities storeDB = new GetMedEntities();
        //
        // GET: /Store/
        public ActionResult Index()
        {
            var categories = storeDB.Categories.ToList();

            return View(categories);
        }
    }
}

SampleData.cs：

using System.Data.Entity;

namespace GetMed.Models
{
    public class SampleData : DropCreateDatabaseIfModelChanges<GetMedEntities>
    {
        protected override void Seed(GetMedEntities context)
        {
            var categories = new List<Category>
            {
                new Category { Name = "Infections" },
                new Category { Name = "Antibiotics" },
                new Category { Name = "Vitamins" },
                new Category { Name = "Cosmetics" }
            };
        }
    }
}

GetMedEntities.cs

namespace GetMed.Models
{
    public class GetMedEntities : DbContext
    {
        public DbSet<Category> Categories { get; set; }
    }
}

Index.cs：

@model IEnumerable<GetMed.Models.Category>

@{
    ViewBag.Title = "Index";
}

<h3>Browse Categories</h3>
<p>Select from @Model.Count() categories:</p>
<ul>
    @foreach (var category in Model)
    {
        <li>@Html.ActionLink(category.Name, "Browse", new { category = category.Name })</li>
    }
</ul>

Answer 1

如果查看数据库，您会发现其中没有数据。看看你的Seed方法：你期望它做什么？

创建数据后，您还需要执行两个步骤：

将其添加到DbContext
将其保存到数据库

这导致了这些额外的行：

context.Categories.AddRange(categories);
context.SaveChanges();

Answer 2

永远不要初始化EF背景，一旦它会打击你，相信我

通过EF向DB添加记录时，您必须致电

using (var context = new GetMedEntities)
{
    // YOUR ADD ROUTINE GOES HERE

    context.SaveChanges();
}

<强>更新

更改班级SampleData

    public class SampleData : DropCreateDatabaseIfModelChanges<GetMedEntities>
    {
        protected override void Seed(GetMedEntities context)
        {
//I STRICTLY RECOMMEND NOT TO PROVIDE CONTEXT AS A METHOD PARAMETER 
//YOU HAVE TO WRITE PROPER DB LAYER TO DO SO

            context.Categories.AddRange( new List<Category>()
            {
                new Category { Name = "Infections" },
                new Category { Name = "Antibiotics" },
                new Category { Name = "Vitamins" },
                new Category { Name = "Cosmetics" }
            });
            context.SaveChanges();
        }
    }

但简单的解决方案如下：

public class SampleData 
{
  public void SeedSampleData() 
  {
    var context = new GedMedEntities();
    context.Categories.AddRange( new List<Category>()
    {
      new Category { Name = "Infections" },
      new Category { Name = "Antibiotics" },
      new Category { Name = "Vitamins" },
      new Category { Name = "Cosmetics" }
    });
    context.SaveChanges();

无法从EF数据库中检索数据

2 个答案: