EF 错误：在前一个异步操作完成之前在此上下文上启动了第二个操作

Question

我是 Blazor 的新手，并且在服务器端 Blazor 应用程序（.NET 5）中工作具有以下内容：

我有以下表格：

 <EditForm Model="@MyObject" OnValidSubmit="Submit">
      <DataAnnotationsValidator />
      <ValidationSummary />

     <InputText id="name" @bind-Value="MyObject.Name" />

     <button type="submit">Submit</button>
</EditForm>

后面的代码：

public MyObject MyObject { get; set; } = new MyObject();
    
[Inject]
private IMyObjectService myObjectService { get; set; }

[Inject]
private NavigationManager navigationManager { get; set; }

void Submit()
{
    var created = myObjectService.CreateMyObject(MyObject);

    if (created != null)
    {
        navigationManager.NavigateTo("myobjects/manage");
    } else
    {
        // do something
    }
}

回购：

private readonly ApplicationDbContext _dbContext;

public MyObjectRepo(ApplicationDbContext dbContext)
{
   _dbContext = dbContext;
}

public async Task<MyObject> CreateMyObject(MyObject MyObject)
{
   _dbContext.Add(MyObject);
   await _dbContext.SaveChangesAsync();
   return MyObject;
}

public async Task<bool> DoesMyObjectExistByName(string name)
{
    var exists = await _dbContext.MyObjects.AnyAsync(x => x.Name == name);

    if (exists) return true;
    return false;
}

然后我有一个MyObjectService ：

private readonly IMyObjectRepo _myObjectRepo ;
        
public MyObjectService(IMyObjectRepo myObjectRepo  )
{
    _myObjectRepo  = myObjectRepo;
}

public async Task<MyObject> CreateMyObject(MyObject MyObject)
{
   if (MyObject == null) throw new ArgumentNullException("MyObject cannot be null.");

   // THIS LINE THROWS THE EF ERROR
   var exists = await _myObjectRepo.DoesMyObjectExistByName(MyObject.Name);

   if (!exists)
   {
      return await _myObjectRepo.CreateMyObject(MyObject);
   } else
   {
      return null;
   }
}

但是每次我调用服务的 createMyObject 方法时，EF 都会抛出一个错误：

错误：System.InvalidOperationException：在前一个操作完成之前，在此上下文上启动了第二个操作。 这通常是由不同的线程同时使用同一个 DbContext 实例引起的。

在 Startup.cs (.NET 5) 中，我配置了瞬态生命周期。

services.AddDbContext<ApplicationDbContext>(options =>
        options.UseSqlServer(Configuration.GetConnectionString("Default")),
        ServiceLifetime.Transient);

services.AddAutoMapper(typeof(Startup));
services.AddScoped<IMyObjectRepo, MyObjectRepo>();
services.AddScoped<IMyObjectService, MyObjectService>();

我想我正在使用所有正确的语法来实现异步/等待和线程安全，有什么想法吗？

Answer 1

我自己对Blazor不熟悉，但我认为您的Submit方法应该如下所示 -

async void Submit()
{
    var created = await myObjectService.CreateMyObject(MyObject);

    if (created != null)
    {
        navigationManager.NavigateTo("myobjects/manage");
    } else
    {
        // do something
    }
}

基本上，您缺少 async/await 关键字。