1. 配置提供商
   • 文件格式(INI, JSON, XML)
   • 命令行参数
   • 环境变量
   • 内存中的.NET对象
   • 未加密的Secret管理存储
   • 加密的用户存储, 例如Azure秘钥库
   • 自定义的提供商
2. JSON配置文件
   • 默认 appsettings.json 注意：后加载的值会覆盖。
     
     Default
     
     
     多配置
   • 取得配置
     • IConfiguration[“Key:ChildKey”]
     • 针对”ConnectionStrings:xxx”, 可以使用IConfiguration. GetConnectionString(“xxx”)

public static IConfiguration Configuration;
public StartupDevelopment(IConfiguration configuration)
{
    Configuration = configuration;
}

 public void ConfigureServices(IServiceCollection services)
{
     services.AddMvc();

   //注册Dbcontxt
     services.AddDbContext<ApplicationContext>(options =>
      {
         //var connectionString = "Data Source = 10.30.0.14; Database = Blog.db; User = sa; Password = Hello,MMOC";
         //var connectionString = "Data Source = .;Database = Blog.db;Integrated Security=True";
         //var connectionString = Configuration["ConnectionStrings:DefaultConnection"];
         var connectionString = Configuration.GetConnectionString("DefaultConnection");
              options.UseSqlServer(connectionString);
      });
           ...
}

• 其他文件配置
  ConfigurationBuilder().AddJsonFile("appsettings.json").Build() 返回IConfigurationRoot，继承于IConfiguration. 使用接口IConfiguration即可。