URL地址記住不咋辦，代碼生成走一波。

“頭疼”

自己在用Angular做項目時，前端要請求后端數據時的代碼如下

this.http.get("url/xxx")

這是請求一個URL地址數據最簡單的代碼，但是如此簡單的代碼還會遇到一些頭疼的問題

• URL地址拼寫錯誤，有可能折騰半天才發現😑
• 后端修改了地址沒通知到前端，測試不到位就炸了，不是所有項目都有那么規范的接口變更流程😑
• 查看代碼的時候，看着URL地址，這個地址用途是哈？還要翻接口文檔😑

“吃葯”

為了解決這個問題，我們需要一個包含所有接口的文件

import { environment } from 'src/environments/environment';
export const WebAPI = {
  /** 授權控制器 */
  Auth: {
  	/** */
    Controller: `${environment.host}/api/Auth`,
    /** GET 獲得用戶 */
    GetUser: `${environment.host}/api/Auth/GetUser`,
    /** POST 登陸 */
    Login: `${environment.host}/api/Auth/Login`,
  },
}

那么請求代碼就可以改成

this.http.get(WebAPI.Auth.GetUser)

但是維護這個文件是件吃力的事情，作為一個時刻想着如何偷懶的程序員，吃力的事情就讓計算機去干，所以寫一個代碼生成工具。

工具代碼

    public static class BuildWebApiToTS
    {
        public static string Build(Assembly assembly, string prefix = "api/")
        {
            List<Controller> controllers = GetApis(assembly);
            string code = CreateCode(controllers);
            return code.ToString();
        }
        
        public static void BuildToFile(Assembly assembly, string path, string prefix = "api/")
        {
            var code = Build(assembly, prefix);
            string existsCode = "";
            if (System.IO.File.Exists(path) == true)
                existsCode = System.IO.File.ReadAllText(path);

            if (existsCode != code)
                System.IO.File.WriteAllText(path, code);
        }

        #region 構造代碼

        public static string CreateCode(List<Controller> controllers, string prefix = "api/")
        {
            StringBuilder code = new StringBuilder();
            code.AppendLine("import { environment } from 'src/environments/environment';");
            code.AppendLine("export const WebAPI = {");
            foreach (var coll in controllers.OrderBy(x => x.Name))
            {
                code.AppendLine($"  /** {coll.ApiComments?.Title} */");
                code.AppendLine($"  {coll.Name}: {{");
                code.AppendLine($"    Controller: `${{environment.host}}/{prefix}{coll.Name}`,");
                foreach (var action in coll.Actions.OrderBy(x => x.Name))
                {
                    code.AppendLine($"    /** {action.Type} {action.ApiComments?.Title} */");
                    code.AppendLine($"    {action.Name}: `${{environment.host}}/{prefix}{coll.Name}/{action.Name}`,");
                }
                code.AppendLine($"  }},");
            }
            code.AppendLine($"}};");
            return code.ToString();
        }

        #endregion

        #region 獲得接口清單

        public static List<Controller> GetApis(Assembly assembly)
        {
            List<Controller> controllers = new List<Controller>();
            var collTypes = assembly.GetTypes().Where(x => x.GetCustomAttributes(typeof(ApiControllerAttribute), false).Count() > 0);
            foreach (var collType in collTypes)
            {
                var controller = new Controller(collType.Name.Replace("Controller", ""));
                controller.ApiComments = collType.GetCustomAttribute<ApiCommentsAttribute>();
                controllers.Add(controller);
                controller.Actions.AddRange(GetTypeMembers(collType, typeof(HttpGetAttribute), "GET"));
                controller.Actions.AddRange(GetTypeMembers(collType, typeof(HttpPostAttribute), "POST"));
                controller.Actions.AddRange(GetTypeMembers(collType, typeof(HttpPutAttribute), "PUT"));
                controller.Actions.AddRange(GetTypeMembers(collType, typeof(HttpDeleteAttribute), "DELETE"));
            }
            return controllers;
        }
        private static List<Action> GetTypeMembers(Type type, Type whereType, string saveType)
        {
            var actonTypes = type.GetMembers().Where(x => x.GetCustomAttributes(whereType, false).Count() > 0);
            List<Action> actons = new List<Action>();
            foreach (var actonType in actonTypes)
            {
                var action = new Action(saveType, actonType.Name);
                action.ApiComments = actonType.GetCustomAttribute<ApiCommentsAttribute>();
                actons.Add(action);
            }
            return actons;
        }

        public record Controller(string Name)
        {
            public ApiCommentsAttribute ApiComments { get; set; }
            public List<Action> Actions { get; set; } = new List<Action>();
        }

        public record Action(string Type, string Name)
        {
            public ApiCommentsAttribute ApiComments { get; set; }
        }

        #endregion
    }

    public class ApiCommentsAttribute : Attribute
    {
        public string Title { get; set; }
        public ApiCommentsAttribute(string title)
        {
            Title = title;
        }
    }

使用代碼

#if DEBUG
	BuildWebApiToTS.BuildToFile(typeof(Program).Assembly, "ClientApp/src/app/web-api.ts");
#endif

上面代碼大概的流程就是

1. 利用反射讀取程序集中包含ApiControllerAttribute特性的類
2. 利用發射讀取HttpGetAttribute、HttpPostAttribute、HttpPutAttribute、HttpDeleteAttribute特性的方法
3. 根據需要的格式生成代碼
4. 將代碼文件寫入ClientApp/src/app/web-api.ts

有了這個東西帶來以下好處

1. URL地址拼寫錯誤問題，不存在的🎉
2. 后端修改了接口，前端直接編譯不過，立即發現問題🎉
3. 鼠標停留，接口注釋就顯示了🎉