无法访问已处置的上下文实例 EF 核心

Question

我正在通过 .net core mvc 和 EF 开发 CRM，它需要大量的数据库连接来检索和更新信息。调试时时不时遇到这个错误，这是一个大项目，有很多用户，我不知道它在实际使用中如何工作！

Cannot access a disposed context instance. A common cause of this error is disposing a context instance that was resolved from dependency injection and then later trying to use the same context instance elsewhere in your application. This may occur if you are calling 'Dispose' on the context instance, or wrapping it in a using statement. If you are using dependency injection, you should let the dependency injection container take care of disposing context instances.\r\nObject name: 'XXX'.

我在 startup.cs 中使用此设置之前：

services.AddDbContext<XXX>
                (option => 
                option.UseSqlServer(Configuration.GetConnectionString("YYY"))
                .ServiceLifetime.Singleton);

该设置偶尔会导致另一个错误：

System.InvalidOperationException: The instance of entity type 'TblZZZ' cannot be tracked because another instance with the same key value for {'ZZZId'} is already being tracked. When attaching existing entities, ensure that only one entity instance with a given key value is attached.

所以我将设置更改为：

services.AddDbContext<XXX>
                (option => 
                option.UseSqlServer(Configuration.GetConnectionString("YYY"))
                .UseQueryTrackingBehavior(QueryTrackingBehavior.NoTracking));

现在我正面临Cannot access a disposed context instance。我不知道什么设置可以解决我的问题。

我用的是net5.0

更新：我的部分 class:

public partial class TblXXX
    {
        private ZZZ context;//context
        public TblXXX(ZZZ _context)
        {
            context = _context;
        }
        public TblXXX() { }
//function for check username
   public bool CheckUsernameExit(string username) {
            var u = context.TblXXX
                .Where(e => e.Username == username)
                .FirstOrDefault();
            return (u != null);
        }
}

在我的控制器中：

  public IActionResult Check(UserModelView user)
        {
            if (ModelState.IsValid)
            {
                var r = _viewModel.tblXXX.CheckUsernameExit(user.tblXXX.Username);
                if (r)
                {
                    toastNotification.AddErrorToastMessage("This email is in use. Enter differernt email.");
                 
                    return View("Create", _viewModel);
                }

这是我的 ViewModel：

 public class UserModelView
    {
        public TblXXX tblXXX { get; set; }
        public List<TblXXX > tblXXXList { get; set; }
    }

这是我遇到错误的情况之一。

Answer 1

在 asp.net 核心中，DbContext 应该是 Scoped 服务，而不是 Singleton。

改变这个：

services.AddDbContext<XXX>
                (option => 
                option.UseSqlServer(Configuration.GetConnectionString("YYY"))
                .ServiceLifetime.Singleton);

到

services.AddDbContext<XXX>
                (option => 
                option.UseSqlServer(Configuration.GetConnectionString("YYY")));

Answer 2

我收到此错误是因为我没有在控制器方法内的方法上使用 await。这导致函数 return 并在调用完成之前处理上下文。

无法访问已处置的上下文实例 EF 核心

Cannot access a disposed context instance EF core

c#

database

entity-framework

dependency-injection

asp.net-core

我用的是net5.0