EF Core如何在类实例中获取DBContext? [英] EF Core how to get a DBContext in a class instance?

问题描述

ASP NET Core项目使用实体框架核心.

The ASP NET Core project uses the Entity Framework Core.

从Home控制器的方法中，我调用Task.Run，​​以获取类 MyClass 的实例的方法，在这里我需要从数据库访问数据.

From the method of the Home controller I call Task.Run for the method of the instance of the class MyClass, where I need to access the data from the database.

我试图将 _dbContext 传递给 MyClass 类的构造函数，但出现异常

I tried to pass _dbContext to the constructor of the MyClass class, but I get the exception

无法访问已处置的对象.

Cannot access a disposed object.

HomeController

[Route("api/[controller]")]
[EnableCors("AllowAllOrigin")]
[ApiController]
public class HomeController : ControllerBase
{
   private readonly DataBaseContext _dbContext;

   public HomeController (DataBaseContext dbContext)
   {
      _dbContext = dbContext;
   }

   [EnableCors("AllowAllOrigin")]
   [HttpPost("[action]")]
   public string UpdateBotSettings()
   {
      MyClass myClass = new MyClass(_dbContext);
      Task task = Task.Run(() => myClass.AnyMethod());
   }
}

MyClass

public class MyClass
{
   private readonly DataBaseContext _dbContext;

   public MyClass(DataBaseContext dbContext)
   {
      _dbContext = dbContext;
   }

   public async void AnyMethodAsync()
   {
      MyData myData = _dbContext.AnyData.Where(d => d.id == 1).FirstOrDefault(); // <- exception
   }
}

启动

public void ConfigureServices(IServiceCollection services)
{
  services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_2);

  string connection = Configuration.GetConnectionString("ConnectionDB");
  services.AddDbContext<DataBaseContext>(options =>  options.UseSqlServer(connection));
  // another code
}

能否请您告诉我如何在MyClass实例内部访问dbContext?

Can you please tell me how to access dbContext inside an instance of MyClass?

推荐答案

代码中最重要的错误是您在 AnyMethodAsync()方法中使用了 async void Myclass 的代码.不要在代码中使用 async void ，而是使用 async Task .详细信息如下: C#–注意您的代码中的异步无效

Most important mistake in your code is that you are using async void in your AnyMethodAsync() method of the Myclass. Don't use async void in your code, instead use async Task. Here is the details: C# – beware of async void in your code

因此，如下所示编写您的 AnyMethodAsync():

So write your AnyMethodAsync() as follows:

public async Task AnyMethodAsync()
{
   MyData myData = await _dbContext.AnyData.Where(d => d.id == 1).FirstOrDefault(); 
}

现在，您可以如下所示将 MyClass 注册到ASP.NET Core DI容器:

Now you can register your MyClass to the ASP.NET Core DI container as follows:

public void ConfigureServices(IServiceCollection services)
{
   services.AddScoped<MyClass>(); // <-- here it is

   string connection = Configuration.GetConnectionString("ConnectionDB");
   services.AddDbContext<DataBaseContext>(options =>  options.UseSqlServer(connection));
   // another code
   services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_2);
}

现在按如下方式使用它:

Now use it as follows:

[Route("api/[controller]")]
[EnableCors("AllowAllOrigin")]
[ApiController]
public class HomeController : ControllerBase
{
   private readonly DataBaseContext _dbContext;
   private readonly MyClass _myClass

   public HomeController (DataBaseContext dbContext, MyClass myClass)
   {
      _dbContext = dbContext;
      _myClass = myClass;
   }

   [EnableCors("AllowAllOrigin")]
   [HttpPost("[action]")]
   public async Task<string> UpdateBotSettings()
   {
      await _myClass.AnyMethod();

      // rest of codes
   }
}

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