給 IConfiguration 寫一個 GetAppSetting 擴展方法

Intro

在 .net core 中，微軟已經預設使用 appsettings.json 來代替 app.config，並重新設計了一套完整的配置系統，可以支持 json/xml/ini/環境變數等。

在 .net core 中有一個 GetConnectionString 的擴展方法用來比較方便的獲取鏈接字元串，類似於在 .net framework 中使用 ConfigurationManager.ConnectionStrings["key"] 來獲取鏈接字元串。

這次來參考 GetConnectionString 實現一個 GetAppSetting，類似於 .net framework 中使用 ConfigurationManager.AppSettings 來獲取配置值。

實現代碼

GetConnectionString 是獲取 ConnectionStrings 這個節點下的某個配置，
GetAppSetting 來獲取 AppSettings 這個節點下的某個配置

實現代碼：

        /// <summary>
        /// GetAppSetting
        /// Shorthand for GetSection("AppSettings")[key]
        /// </summary>
        /// <param name="configuration">IConfiguration instance</param>
        /// <param name="key">appSettings key</param>
        /// <returns>app setting value</returns>
        public static string GetAppSetting([NotNull]this IConfiguration configuration, string key)
        {
            return configuration.GetSection("AppSettings")[key];
        }

        /// <summary>
        /// GetAppSetting
        /// Shorthand for GetSection("AppSettings")[key]
        /// </summary>
        /// <param name="configuration">IConfiguration instance</param>
        /// <param name="key">appSettings key</param>
        /// <returns>app setting value</returns>
        public static T GetAppSetting<T>([NotNull]this IConfiguration configuration, string key)
        {
            return configuration.GetSection("AppSettings")[key].To<T>();
        }

        /// <summary>
        /// GetAppSetting
        /// Shorthand for GetSection("AppSettings")[key]
        /// </summary>
        /// <param name="configuration">IConfiguration instance</param>
        /// <param name="key">appSettings key</param>
        /// <param name="defaultValue">default value if not exist</param>
        /// <returns>app setting value</returns>
        public static T GetAppSetting<T>([NotNull] this IConfiguration configuration, string key, T defaultValue)
        {
            return configuration.GetSection("AppSettings")[key].ToOrDefault(defaultValue);
        }

        /// <summary>
        /// GetAppSetting
        /// Shorthand for GetSection("AppSettings")[key]
        /// </summary>
        /// <param name="configuration">IConfiguration instance</param>
        /// <param name="key">appSettings key</param>
        /// <param name="defaultValueFunc">default value func if not exist to get a default value</param>
        /// <returns>app setting value</returns>
        public static T GetAppSetting<T>([NotNull] this IConfiguration configuration, string key, Func<T> defaultValueFunc)
        {
            return configuration.GetSection("AppSettings")[key].ToOrDefault(defaultValueFunc);
        }

查看源碼

使用

使用起來和 GetConnectionString 差不多

測試 appsettings.json

{
  "ConnectionStrings": {
    "TestDb": "server=.;database=Test;uid=weihanli;pwd=Admin888"
  },
  "AppSettings":{
    "Number": 12,
    "City": "Shanghai"
  }
}

GetAppSetting 示例

        IConfiguration configuration = new ConfigurationBuilder()
            // ...
            .AddJsonFile("appsettings.json")
            .Build();

        var city = configuration.GetAppSetting("City");
        var number = configuration.GetAppSetting<int>("Number");
        System.Console.WriteLine($"City:{city}, Number:{number}");