深入理解.NET Core中的配置Configuration的方法

public interface IConfigurationSource
{
    IConfigurationProvider Build(IConfigurationBuilder builder);
}

public interface IConfigurationProvider
{
	//读取配置
    bool TryGet(string key, out string? value);
    //修改配置
    void Set(string key, string? value);
    //获取重载配置的Token
    IChangeToken GetReloadToken();
    //载入配置
    void Load();
    //获取指定父路径下的直接子节点Key，然后 Concat(earlierKeys) 一同返回
    IEnumerable<string> GetChildKeys(IEnumerable<string> earlierKeys, string? parentPath);
}

public interface IConfigurationBuilder
{
	//保存Build的一些公开的字典属性，有需要的化可以使用该字段存放一些变量
    IDictionary<string, object> Properties { get; }
    //来自多个地方的配置源集合
    IList<IConfigurationSource> Sources { get; }
    //向Sources属性中添加一个配置源
    IConfigurationBuilder Add(IConfigurationSource source);
    //基于所有配置源生成一个全局的配置，供程序读写，一般我们都是用这个接口对配置进行读写。
    IConfigurationRoot Build();
}

 public class ConfigurationBuilder : IConfigurationBuilder
 {
     private readonly List<IConfigurationSource> _sources = new();
     public IList<IConfigurationSource> Sources => _sources;
     public IDictionary<string, object> Properties { get; } = new Dictionary<string, object>();
     public IConfigurationBuilder Add(IConfigurationSource source)
     {
         ThrowHelper.ThrowIfNull(source);
         _sources.Add(source);
         return this;
     }
     public IConfigurationRoot Build()
     {
         var providers = new List<IConfigurationProvider>();
         foreach (IConfigurationSource source in _sources)
         {
             IConfigurationProvider provider = source.Build(this);
             providers.Add(provider);
         }
         return new ConfigurationRoot(providers);
     }
 }

public interface IConfiguration
{
	//获取或设置配置
    string? this[string key] { get; set; }
	//获取指定key的配置子节点
    IConfigurationSection GetSection(string key);
	//获取当前配置的直接子节点列表
    IEnumerable<IConfigurationSection> GetChildren();
    //当配置发生变更时的token
    IChangeToken GetReloadToken();
}

public interface IConfigurationRoot : IConfiguration
{
	//强制重载所有配置
    void Reload();
    //所有配置提供程序
    IEnumerable<IConfigurationProvider> Providers { get; }
}

public class DataBaseConfigurationSource : IConfigurationSource
{
    public IConfigurationProvider Build(IConfigurationBuilder builder)
    {
        return new DataBaseConfigurationProvider();
    }
}
public class DataBaseConfigurationProvider : ConfigurationProvider
{
    public override void Load()
    {
        base.Load();
        //读取数据库配置
    }
}
public static class DataBaseConfigurationExtensions
{
    public static IConfigurationBuilder AddDb(this IConfigurationBuilder configurationBuilder)
    {
        configurationBuilder.Sources.Add(new DataBaseConfigurationSource());
        return configurationBuilder;
    }
}

static void Main(string[] args)
{
    var builder = new ConfigurationBuilder()
        .AddDb()
        .Build();
    var value = builder["key"];
}