Entity Framework Core - 迁移 - 没有为此对象定义无参数构造函数

我正在 Visual Studio 2017 中使用最新的 .Net Core 和 EF Core。我创建了一个模型，并且运行良好。此后我进行了一些修改，当我尝试添加新的迁移时收到以下错误：

Build succeeded.
  0 Warning(s)
  0 Error(s)

Time Elapsed 00:00:09.08
System.MissingMethodException: No parameterless constructor defined for this object.
  at System.RuntimeTypeHandle.CreateInstance(RuntimeType type, Boolean publicOnly, Boolean noCheck, Boolean& canBeCached, RuntimeMethodHandleInternal& ctor, Boolean& bNeedSecurityCheck)
  at System.RuntimeType.CreateInstanceSlow(Boolean publicOnly, Boolean skipCheckThis, Boolean fillCache, StackCrawlMark& stackMark)
  at System.Activator.CreateInstance(Type type, Boolean nonPublic)
  at System.Activator.CreateInstance(Type type)
  at Microsoft.EntityFrameworkCore.Design.Internal.DbContextOperations.<>c__DisplayClass12_0.<FindContextTypes>b__3()
  at Microsoft.EntityFrameworkCore.Design.Internal.DbContextOperations.CreateContext(Func`1 factory)
  at Microsoft.EntityFrameworkCore.Design.Internal.DbContextOperations.CreateContext(String contextType)
  at Microsoft.EntityFrameworkCore.Design.Internal.MigrationsOperations.AddMigration(String name, String outputDir, String contextType)
  at Microsoft.EntityFrameworkCore.Design.OperationExecutor.AddMigrationImpl(String name, String outputDir, String contextType)
  at Microsoft.EntityFrameworkCore.Design.OperationExecutor.OperationBase.<>c__DisplayClass3_0`1.<Execute>b__0()
  at Microsoft.EntityFrameworkCore.Design.OperationExecutor.OperationBase.Execute(Action action)
No parameterless constructor defined for this object.

自上次签入以来，我比较了我的代码，并注释掉了某些代码块，以查看错误是否仍然存在，无论我注释掉什么，它仍然会因相同的错误而失败。

问题：有没有办法获得有关哪些类型没有无参数构造函数的更详细信息？或者甚至从 VS 中运行它并可能得到一个断点？

Update:根据一些评论，这里是一些代码。

For the DbContext覆盖

public class AlmanacDb : IdentityDbContext<ApplicationUser, ApplicationRole, int> {

  private readonly ILogger logger;

  public AlmanacDb(DbContextOptions<AlmanacDb> options, ILoggerFactory loggerFactory) : base(options) {
    this.logger = loggerFactory.CreateLogger<AlmanacDb>();
  }

  protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder) {
    optionsBuilder.UseSqlServer("Server=.\\SQLExpress;Database=Almanac;Trusted_Connection=True;MultipleActiveResultSets=True;");
  }

  ...
}

我确实有一个IDbContextFactory但它没有在任何地方被引用，并且在没有引用的情况下工作。根据第二条评论中提供的链接不确定这是否是一个问题。如果没记错的话，只要IDbContextFactory是在解决方案内，它应该找到它吗？

public class AlmanacDbFactory : IDbContextFactory<AlmanacDb> {

  private IConfigurationRoot configuration;
  private readonly ILoggerFactory loggerFactory;

  public AlmanacDbFactory(ILoggerFactory loggerFactory) {
    var builder = new ConfigurationBuilder()
     .SetBasePath(System.AppContext.BaseDirectory)
     .AddJsonFile("appsettings.json", optional: false, reloadOnChange: true);

    this.configuration = builder.Build();
    this.loggerFactory = loggerFactory;
  }

  public AlmanacDb Create(DbContextFactoryOptions options) {
    var optionsBuilder = new DbContextOptionsBuilder<AlmanacDb>();
    optionsBuilder.UseSqlServer(
      configuration.GetConnectionString("AlmanacSQL"), m => { m.EnableRetryOnFailure(); }
    );

    return new AlmanacDb(optionsBuilder.Options, loggerFactory);
  }
}

My Startup.cs class

public void ConfigureServices(IServiceCollection services) {
  try {
    services.AddDbContext<AlmanacDb>(options =>
      options.UseSqlServer(Configuration.GetConnectionString("AlmanacSQL"))
    );
    services.AddScoped(typeof(IRepository<>), typeof(Repository<>));

    services.AddIdentity<ApplicationUser, ApplicationRole>()
      .AddEntityFrameworkStores<AlmanacDb, int>()
      .AddDefaultTokenProviders();

    services.AddScoped<SignInManager<ApplicationUser>, AvantiaSignInManager<ApplicationUser>>();

    services.AddAuthorization(x => {
      x.AddPolicy("EmployeeOnly", p => p.RequireClaim("EmployeeNumber"));
    });

    services.AddMvc();
  } catch (Exception e) {
    Console.WriteLine(e.ToString());
    throw;
  }
}

public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory, AlmanacDb context) {
  ... // Nothing actually touches the AlmanacDb within this code so I left it out
}

更新2：解决方案看到我正在学习 ASP.Net Core，我正在阅读大量网站（包括 learn.microsoft.com），我曾经将其放入IDbContextFactory代码如上面所示。我从代码中删除了它，错误消失了，所有内容都构建并创建了迁移。

我将把 @alessalessio 标记为答案，因为我假设（尚未测试）取出ILoggerFactory loggerFactory内的依赖性AlmanacDbFactory构造函数也能达到这个目的。

设计时工具尝试自动查找应用程序如何创建 DbContext 类型的实例。如果 EF 找不到合适的方法来初始化您的 DbContext，您可能会遇到此错误。

选项： 1-创建一个无参数构造函数

  public AlmanacDb() { }
  protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
  {           
       optionsBuilder.UseSqlServer(_connString);
  }

  private readonly string _connString = "<your conn string>";

2-

public AlmanacDb Create()
{
     var optionsBuilder = new DbContextOptionsBuilder<AlmanacDb>();
     optionsBuilder.UseSqlServer(connectionString);

     return new AlmanacDb(optionsBuilder.Options);
}

https://learn.microsoft.com/en-us/ef/core/miscellaneous/configuring-dbcontext https://learn.microsoft.com/en-us/ef/core/miscellaneous/configuring-dbcontext