为什么ASP.NET SPA模板会为所有请求实例化UserManager一次？

Question

我正在使用VS2013 ASP.NET SPA模板作为我的Web应用程序的起点,它使用新的ASP.NET身份框架.这是来自模板:

public partial class Startup
 {
     static Startup()
     {
     UserManagerFactory = () => new UserManager<IdentityUser>(new UserStore<IdentityUser>());
....
}

因此,由于没有将DbContext传递到上面的UserStore构造函数,这表明正在创建一个新的DbContext.由于我也想利用数据上下文(对于请求期间的其他数据操作),我稍微更改了模板代码:

public partial class Startup
 {
public static DerivedDbContext=null;

    static Startup()
    {
   context = new DerivedDbContext();
           UserManagerFactory = () => new UserManager<IdentityUser>(new UserStore<IdentityUser>(context));
...
}

现在,我可以通过以下方式从我的任何控制器使用相同的DbContext:

Startup.context

但是,当多个请求同时进入时我遇到了麻烦,因为无关的操作发生在同一个DbContext中.从这里开始,我向我指出,我不应该在应用程序的整个生命周期中实例化单个DbContext,而只是为了特定请求的生命周期,所以我将实例化移动到控制器的构造函数,但现在,我在控制器中有自己的DbContext,而UserManager仍然有自己的(并且在Startup类中创建).

为什么模板为所有用户(在Startup类中)实例化了一次UserManager？值得关注的是,通过在控制器构造函数中创建自己的DbContext,有两个DbContexts(我在控制器的构造函数中创建的那个,以及在UserManager中创建的那个,在Startup类中创建的)同时播放？在所有请求中共享一个UserManager是否可以接受,但在一般情况下在所有请求中共享一个DbContext是不可接受的？

有两个单独的上下文似乎是愚蠢的,我注意到我有时会得到一个不同步的数据视图.我想了解是否有其他人在使用此模板时遇到此问题.

**编辑:我理解像nInject这样的IOC框架可能有助于在这种情况下管理对象生命周期,但我想首先了解如何在没有这种框架的帮助下实现这一目标.

谢谢... - 贝恩

Answer 1

因此，该模式应该是每个请求一个 UserManager 和一个 DbContext。在 2.0-alpha1 版本中，我们尝试通过添加一些新的身份中间件来简化这两个任务：

我们正在开发一个更新的示例包来演示这些，但与此同时

您可以使用新包添加以下内容到 IdentityModels.cs/Startup.Auth.cs 中：

public class ApplicationUser : IdentityUser
{
    public async Task<ClaimsIdentity> GenerateUserIdentityAsync(UserManager<ApplicationUser> manager)
    {
        // Note the authenticationType must match the one defined in CookieAuthenticationOptions.AuthenticationType
        var userIdentity = await manager.CreateIdentityAsync(this, DefaultAuthenticationTypes.ApplicationCookie);
        // Add custom user claims here
        return userIdentity;
    }
}

public class ApplicationDbContext : IdentityDbContext<ApplicationUser>
{
    public ApplicationDbContext()
        : base("DefaultConnection")
    {
    }

    public static ApplicationDbContext Create() {
        return new ApplicationDbContext();
    }
}

public class ApplicationUserManager : UserManager<ApplicationUser> {
    // Configure the application user manager
    public ApplicationUserManager(IUserStore<ApplicationUser> store) : base(store) {
    }

    public static ApplicationUserManager Create(IdentityFactoryOptions<ApplicationUserManager> options) {
        var manager = new ApplicationUserManager(new UserStore<ApplicationUser>(options.Context.GetDbContext()));
        //var manager = new ApplicationUserManager(new AzureStore<ApplicationUser>());
        manager.UserValidator = new UserValidator<ApplicationUser>(manager) {
            AllowOnlyAlphanumericUserNames = false,
            RequireUniqueEmail = true
        };
        manager.PasswordValidator = new MinimumLengthValidator(6);
        var dataProtectionProvider = options.DataProtectionProvider;
        if (dataProtectionProvider != null) {
            manager.PasswordResetTokens = new DataProtectorTokenProvider(dataProtectionProvider.Create("PasswordReset"));
            manager.UserConfirmationTokens = new DataProtectorTokenProvider(dataProtectionProvider.Create("ConfirmUser"));
        }
        return manager;
    }
}

public static class OwinExtensions {
    public static IAppBuilder UseDbContextFactory(this IAppBuilder app, Func<DbContext> createCallback) {
        if (app == null) {
            throw new ArgumentNullException("app");
        }
        if (createCallback == null) {
            throw new ArgumentNullException("createCallback");
        }

        app.Use(typeof(IdentityFactoryMiddleware<DbContext, IdentityFactoryOptions<DbContext>>), 
            new IdentityFactoryOptions<DbContext>() { 
                Provider = new IdentityFactoryProvider<DbContext>() {
                    OnCreate = (options) => createCallback()
                }
            });
        return app;
    }

    public static DbContext GetDbContext(this IOwinContext context) {
        if (context == null) {
            throw new ArgumentNullException("context");
        }
        return context.Get<DbContext>();
    }
}

Startup.Auth.cs 中包含以下内容：

    public void ConfigureAuth(IAppBuilder app) {
        // Configure the db context and user manager to use per request
        app.UseDbContextFactory(ApplicationDbContext.Create);
        app.UseUserManagerFactory(new IdentityFactoryOptions<ApplicationUserManager>() {
            DataProtectionProvider = app.GetDataProtectionProvider(),
            Provider = new IdentityFactoryProvider<ApplicationUserManager>() {
                OnCreate = ApplicationUserManager.Create
            }
        });

        // Enable the application to use a cookie to store information for the signed in user
        // and to use a cookie to temporarily store information about a user logging in with a third party login provider
        // Configure the sign in cookie
        app.UseCookieAuthentication(new CookieAuthenticationOptions {
            AuthenticationType = DefaultAuthenticationTypes.ApplicationCookie,
            LoginPath = new PathString("/Account/Login"),
            Provider = new CookieAuthenticationProvider {
                OnValidateIdentity = SecurityStampValidator.OnValidateIdentity<ApplicationUserManager, ApplicationUser>(
                    validateInterval: TimeSpan.FromSeconds(5),
                    regenerateIdentity: (manager, user) => user.GenerateUserIdentityAsync(manager))
            }
        });
        app.UseExternalSignInCookie(DefaultAuthenticationTypes.ExternalCookie);