您必须删除默认构造函数。换句话说，参数较少的构造函数。之后所有这些都将按预期工作。

You have to remove the default constructor.In other words parameter less constructor.After that all will work as expected.

注意：在运行时调用参数较少的构造方法，而不是此 public MyDbContext（DbContextOptions options）：base（options）{} 。

Note : The reason for that is, the parameter less constructor is being called at run time instead of this public MyDbContext(DbContextOptions options) : base(options) {}.