不带DbContext连接字符串的EF迁移

{
  "ConnectionStrings": {
    "DefaultConnection": "Server=(localdb)\\mssqllocaldb;Database=MyDatabase;Trusted_Connection=True;"
  }
}

public class MyDbContext : DbContext
{
    public MyDbContext(DbContextOptions<MyDbContext> options) : base(options)
    {
    }

    // DbSet和实体类的定义...
}

public static IWebHostBuilder CreateWebHostBuilder(string[] args) =>
    WebHost.CreateDefaultBuilder(args)
        .ConfigureAppConfiguration((hostingContext, config) =>
        {
            config.AddJsonFile("appsettings.json", optional: true, reloadOnChange: true);
        })
        .ConfigureServices((hostingContext, services) =>
        {
            var connectionString = hostingContext.Configuration.GetConnectionString("DefaultConnection");
            services.AddDbContext<MyDbContext>(options => options.UseSqlServer(connectionString));
        })
        .UseStartup<Startup>();