本篇同步發文在個人Blog: 一袋.NET要扛幾樓？打造容器化的ASP.NET Core網站！系列文章 - (19) 建立購物車系統 - 2

1. 建立共通的Infrastructure

1.1 新增InternalServerErrorObjectResult類別

在CartApi專案新增資料夾Infrastructure/ActionResults，並新增InternalServerErrorObjectResult類別且繼承ObjectResult，此類別是用在統一回傳Status Code 500：

using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Mvc;

namespace CartApi.Infrastructure.ActionResults
{
    public class InternalServerErrorObjectResult : ObjectResult
    {
        public InternalServerErrorObjectResult(object error) : base(error)
        {
            StatusCode = StatusCodes.Status500InternalServerError;
        }
    }
}

1.2 新增CartDomainException類別

在CartApi專案新增資料夾Infrastructure/Exceptions，並新增CartDomainException類別且繼承Exception，當一些購物車服務有出問題，可以拋此異常：

using System;

namespace CartApi.Infrastructure.Exceptions
{
    public class CartDomainException : Exception
    {
        public CartDomainException()
        {
        }

        public CartDomainException(string message) : base(message)
        {

        }

        public CartDomainException(string message, Exception innerException) : base(message, innerException)
        {

        }
    }
}

1.3 新增HttpGlobalExceptionFilter類別

在CartApi專案新增資料夾Infrastructure/Filters，並新增HttpGlobalExceptionFilter類別且實作IExceptionFilter，當Controller內部有功能異常時，依此Filter客製化要回傳的HTTP內容：

using CartApi.Infrastructure.ActionResults;
using CartApi.Infrastructure.Exceptions;
using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.Mvc.Filters;
using Microsoft.Extensions.Hosting;
using Microsoft.Extensions.Logging;
using System.Net;

namespace CartApi.Infrastructure.Filters
{
    public class HttpGlobalExceptionFilter : IExceptionFilter
    {
        private readonly IWebHostEnvironment env;
        private readonly ILogger<HttpGlobalExceptionFilter> logger;

        public HttpGlobalExceptionFilter(IWebHostEnvironment env, ILogger<HttpGlobalExceptionFilter> logger)
        {
            this.env = env;
            this.logger = logger;
        }

        public void OnException(ExceptionContext context)
        {
            logger.LogError(new EventId(context.Exception.HResult),
                context.Exception,
                context.Exception.Message);

            if(context.Exception.GetType() == typeof(CartDomainException))
            {
                var json = new JsonErrorResponse
                {
                    Messages = new[] { context.Exception.Message }
                };

                context.Result = new BadRequestObjectResult(json);
                context.HttpContext.Response.StatusCode = (int)HttpStatusCode.BadRequest;
            }
            else
            {
                var json = new JsonErrorResponse
                {
                    Messages = new[] { "An error occured. Try it again" }
                };

                if (env.IsDevelopment())
                {
                    json.DeveloperMessage = context.Exception;
                }

                context.Result = new InternalServerErrorObjectResult(json);
                context.HttpContext.Response.StatusCode = (int)HttpStatusCode.InternalServerError;
            }
            context.ExceptionHandled = true;
        }

        private class JsonErrorResponse
        {
            public string[] Messages { get; set; }
            public object DeveloperMessage { get; set; }
        }
    }
}

2. 修改appSettings.json

在appSettings.json，新增Redis的連線資訊，由於本機有安裝過的Redis，於是配置它為6377 port，對應到Docker的配置仍是預設的6379 port：

• "ConnectionString": "127.0.0.1:6377",

3. 新增CartSettings類別

在CartApi根目錄新增CartSettings.cs類別，只有一個ConnectionString屬性，是用來讀設定檔：

namespace CartApi
{
    public class CartSettings
    {
        public string ConnectionString { get; set; }
    }
}

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之後再來寫Controller和註冊Startup的方法