Question

我正在使用EF6和Identity2 这是我得到的错误：

{“在创建模型时不能使用上下文如果在内部使用上下文，则可能抛出异常 OnModelCreating方法或者如果访问相同的上下文实例并发多个线程。请注意DbContext的实例成员并且不保证相关的类是线程安全的。“}

我也查看了这段代码并且无法弄明白：

"Context cannot be used while the model is being created" exception with ASP.NET Identity

这是我的代码：

Startup.Auth.cs：

namespace IdentitySample {
public partial class Startup {
    // For more information on configuring authentication, please visit http://go.microsoft.com/fwlink/?LinkId=301864
    public void ConfigureAuth(IAppBuilder app) {
        // Configure the db context, user manager and role manager to use a single instance per request
        app.CreatePerOwinContext(ApplicationDbContext.Create);
        app.CreatePerOwinContext<ApplicationUserManager>(ApplicationUserManager.Create);
        app.CreatePerOwinContext<ApplicationRoleManager>(ApplicationRoleManager.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 {
                // Enables the application to validate the security stamp when the user logs in.
                // This is a security feature which is used when you change a password or add an external login to your account.  
                OnValidateIdentity = SecurityStampValidator.OnValidateIdentity<ApplicationUserManager, ApplicationUser>(
                    validateInterval: TimeSpan.FromMinutes(30),
                    regenerateIdentity: (manager, user) => user.GenerateUserIdentityAsync(manager))
            }
        });
        app.UseExternalSignInCookie(DefaultAuthenticationTypes.ExternalCookie);

        // Enables the application to temporarily store user information when they are verifying the second factor in the two-factor authentication process.
        app.UseTwoFactorSignInCookie(DefaultAuthenticationTypes.TwoFactorCookie, TimeSpan.FromMinutes(5));

        // Enables the application to remember the second login verification factor such as phone or email.
        // Once you check this option, your second step of verification during the login process will be remembered on the device where you logged in from.
        // This is similar to the RememberMe option when you log in.
        app.UseTwoFactorRememberBrowserCookie(DefaultAuthenticationTypes.TwoFactorRememberBrowserCookie);

        // Uncomment the following lines to enable logging in with third party login providers
        //app.UseMicrosoftAccountAuthentication(
        //    clientId: "",
        //    clientSecret: "");

        //app.UseTwitterAuthentication(
        //   consumerKey: "",
        //   consumerSecret: "");

        //app.UseFacebookAuthentication(
        //   appId: "",
        //   appSecret: "");

        app.UseGoogleAuthentication();
    }
}

}

这是我的db初始化程序：

        public override void InitializeDatabase(ApplicationDbContext context)
    {
        if (!context.Database.Exists())
        {
            // If database did not exist before, create it
            context.Database.Create();
        }
        else
        {
            // Query to check if MigrationHistory table is present in the database 
            var migrationHistoryTableExists = 
                ((IObjectContextAdapter)context).ObjectContext.ExecuteStoreQuery<int>(
            string.Format(
              "SELECT COUNT(*) FROM information_schema.tables WHERE table_schema = '{0}' " 
                + "AND table_name = '__MigrationHistory'",
              "[worldbigtree.security]"));

            // If MigrationHistory table is not there (which is the case first time we run), create it
            if (migrationHistoryTableExists.FirstOrDefault() == 0)
            {
                if (settings.RecreateDatabase)
                {
                    context.Database.Delete();
                    context.Database.Create();
                    InitializeIdentityForEF(context);
                }
            }
        }


        base.Seed(context);
    }

applicationDbContext：

    public class ApplicationDbContext : IdentityDbContext<ApplicationUser>
{
    public ApplicationDbContext()
        : base("DefaultConnection", throwIfV1Schema: false)
    {
        Database.SetInitializer<ApplicationDbContext>(new MySqlInitializer());
    }

    static ApplicationDbContext()
    {
        // Set the database intializer which is run once during application start
        // This seeds the database with admin user credentials and admin role
        Database.SetInitializer<ApplicationDbContext>(new MySqlInitializer());
    }

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

    public DbSet<Person> People { get; set; }
}

Answer 1

你不能这样做。你的问题的答案是肯定的。在上下文的构造函数中，您正在初始化Database。并且您无法同时执行任何CRUD操作，而初始化数据库尚未完成。您可以插入或选择，但Context用于Database.SetInitializer。我没有试过这个，但是你可以用ADO.NET来检查吗？如果你不能，请检查：ODBC(Open Database Connectivity)

在创建模型时不能使用上下文。 dbContext正在其他地方使用？

1 个答案: