考虑在设计时使用IDbContextFactory来覆盖DbContext的初始化

. NET Core 1.0.1项目，使用实体框架Core和ASP。. NET身份，我有以下上下文:

public class Context : IdentityDbContext<User, Role, Int32, UserClaim, UserRole, UserLogin, RoleClaim, UserToken> { 
  public Context(DbContextOptions options) : base(options) { }
  protected override void OnModelCreating(ModelBuilder builder) {
   base.OnModelCreating(builder);
  }
}

和以下实体:

public class User : IdentityUser<Int32, UserClaim, UserRole, UserLogin> { }
public class Role : IdentityRole<Int32, UserRole, RoleClaim> { }
public class RoleClaim : IdentityRoleClaim<Int32> { }
public class UserClaim : IdentityUserClaim<Int32> { }
public class UserLogin : IdentityUserLogin<Int32> { }
public class UserRole : IdentityUserRole<Int32> { }
public class UserToken : IdentityUserToken<Int32> { }

在启动我有以下:

services.AddDbContext<Context>(x => x.UseSqlServer(connectionString, y => y.MigrationsHistoryTable("__Migrations")));
services
  .AddIdentity<User, Role>()
  .AddEntityFrameworkStores<Context, Int32>()
  .AddDefaultTokenProviders();

当我运行dotnet ef migrations add "FirstMigration"时，我得到以下错误:

在启动时调用'ConfigureServices'方法时发生错误类"WebProject.Startup"。考虑使用IDbContextFactory来在设计时覆盖DbContext的初始化。错误:GenericArguments[0],"WebProject。用户',"Microsoft.AspNetCore.Identity.EntityFrameworkCore.UserStore"4[摘要、TRole TContext, TKey)"违反了类型'TUser'的约束。

如何解决这个问题?