Question

错误： ObjectContext实例已被处理，不能再用于需要连接的操作。

在我的应用程序中呈现视图时，我收到此错误。我已经查看了类似问题的各种SO答案，并且无法解决我的问题。这是我的班级：

public class categoryList
{
    public static Dictionary<string, string> getCategories()
    {
        Dictionary<string, string> myList = new Dictionary<string, string>();
        using (ProductContext context = new ProductContext())
        {
            List<CategoryModel> list = 
                 (from c in context.Categories select c)
                .ToList<CategoryModel>();

            myList = list
              .GroupBy(c => c.category, StringComparer.OrdinalIgnoreCase)
              .ToDictionary(g => g.Key, g => g.First().category, StringComparer.OrdinalIgnoreCase);
            return myList;
        }

    }
}

然后这是我的视图代码调用：

<div class="form-group">
                @Html.LabelFor(model => model.Category, "Category", new { @class = "control-label col-md-2" })
                <div class="col-md-10">
                    @Html.DropDownListFor(model => model.Category.category, newBestPlay.Models.ProductModel.getCategories(), new { @class = "form-control"})
                    @Html.ValidationMessageFor(model => model.Category)
                </div>
            </div>

编辑：为了帮助别人弄清楚我的问题，我粘贴了整个ProductModel类：

public class ProductModel
{
    public int ID { get; set; }

    [Display(Name = "Item #")]
    public int itemNumber { get; set; }

    [Required(ErrorMessage = "Required")]
    [Display(Name = "Product")]
    [MaxLength(50)]
    public String product { get; set; }

    [Required(ErrorMessage = "Required")]
    [Display(Name = "Description")]
    [MaxLength(500)]
    public String description { get; set; }

    [DefaultValue(true)]
    [Display(Name = "Active?")]
    public bool active { get; set; }

    [Display(Name = "Image Name")]
    public String imageName { get; set; }

    [Display(Name = "PDF Name")]
    public String PDFName { get; set; }

    [ForeignKey("Category")]
    public virtual int CategoryID { get; set; }

    public virtual CategoryModel Category { get; set; }

    public IEnumerable<SelectListItem> CategoryList { get; set; }

    public static SelectList getCategories()
    {
        Dictionary<string, string> requestList = newBestPlay.Models.categoryList.getCategories();

        return new SelectList(requestList, "Key", "Value");
    }


}

这是CategoryModel：

public class CategoryModel
{
    public int ID { get; set; }

    [Required(ErrorMessage = "Required")]
    [Display(Name = "Category")]
    [MaxLength(50)]
    public String category { get; set; }

    [DefaultValue(true)]
    [Display(Name = "Active?")]
    public bool active { get; set; }
}

Answer 1

当您的上下文配置为使用LazyLoading时，将抛出此异常。如果启用延迟加载，EF将仅检索您在select子句中指定的对象。

如果“CategoryModel”类包含嵌套对象，并且您正在使用延迟加载，则不会从数据库中检索这些对象。
由于您将select包含在using块中，因此在放置控制器之后，连接以及上下文已经处理完毕。
如果要在视图中引用其中一个内部类对象，例如“Model.InnerClass.Property”，则会出现此异常。

如果之前的陈述属实，您可以尝试以下方法：

public class categoryList
{
   public static Dictionary<string, string> getCategories()
   {
       Dictionary<string, string> myList = new Dictionary<string, string>();
       using (ProductContext context = new ProductContext())
       {
           List<CategoryModel> list = 
                   (from c in context.Categories.Include("PropertyName") select c)
                   .ToList<CategoryModel>();

           myList = list
           .GroupBy(c => c.category, StringComparer.OrdinalIgnoreCase)
           .ToDictionary(g => g.Key, g => g.First().category, StringComparer.OrdinalIgnoreCase);
           return myList;
       }
    }
}

如果内部对象包含其他对象，则应在include中指定该对象，因此EF在处置上下文之前检索该信息：

.Include("InnerProperty.NestedProperty")

我希望它有所帮助

-----编辑1 -----------

以下是代码示例：

public class ProductModel
{
   public virtual CategoryModel Category { get; set; }
}

public class CategoryModel 
{
   public virtual UserAddress Address {get; set;}
}

public class UserAddress
{
   public string Street1 {get; set;}
}

假设以前的型号，Include将如下：

List<CategoryModel> list = (from c in context.Categories
                                             .Include("Category") 
                                             .Include("Category.Address") 
                            select c)
                           .ToList<CategoryModel>();

视图中出错：ObjectContext已被释放

1 个答案: