小编Kho*_*aie的帖子

AsyncLocal为什么从类的异步方法设置字段的值时不保留该值。考虑这个例子：

var scope = new TestScope();

// The default value is 0
Console.WriteLine(scope.Counter.Value);

// Setting the vlaue to 2
await scope.SetValueAsync();

Console.WriteLine(scope.Counter.Value);

class TestScope
{
    public readonly AsyncLocal<int> Counter = new AsyncLocal<int> { Value = 0 };

    public async Task SetValueAsync()
    {
        this.Counter.Value = 2;

        await Task.Yield();
    }
}

预期输出应该是：

0

2

但实际情况是：

0

0

为什么退出方法时异步上下文会发生变化SetValueAsync？

我想OnModelCreating在DbContext. 我需要做什么？

我可以通过DbContext构造函数注入服务。但它似乎不够有效，因为该方法在应用程序启动时被调用一次，我必须为它增肥我的整个 DbContext 类。

public PortalContext(DbContextOptions<PortalContext> options, IPasswordService passwordService) : base(options)
{
    this._passwordService = passwordService;
}

...

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    ...
    entity<User>().HasData(
     new User
     {
       UserName = "admin",
       Password = this._passwordService.EncryptPassword("passw0rd");
     }
    );
    ...
}

上面的代码可以替换为：

public PortalContext(DbContextOptions<PortalContext> options) : base(options)
{
}

...

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    ...
    var passwordService = GetPasswordService(); // How?
    entity<User>().HasData(
     new User
     {
       UserName = "admin",
       Password = passwordService.EncryptPassword("passw0rd");
     }
    );
    ... …