Result模式

专题/后端/DDD/4、Endpoint替换Controller.md

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+当在`Controller`中使用`MediatR`后，业务逻辑被封装了单独的`IRequest`和`IRequestHandler`。但是`Controller`层面违反了单一职责原则。使用`Endpoint`可以做到一个接口一次封装。
+
+
+
+源代码：`F:\demos\CleanArchitecture\UseEndpoint\WebApplication1`

专题/后端/DDD/5、Result模式.md

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+# 引出`Result`模式
+
+
+
+通常的方式
+
+```
+public Customer GetCustomer(int customerId)
+{
+  // more logic
+  return customer;
+}
+
+public Customer CreateCustomer(string firstName, string lastName)
+{
+  // more logic
+  return customer;
+}
+```
+
+在逻辑中，我们可能会判断`customerId`不存在，判断`lastName`没有提供，甚至当前用户是否有权限创建用户。
+
+我们在处理正常和异常这两种情况。
+
+`Result`模式用来对这两种情况进行封装,并且统一了返回结果的格式。
+
+```
+public async Task<Result<BlogCategory>> UpdateAsync(BlogCategory blogCategory)
+{
+    if (Guid.Empty == blogCategory.BlogCategoryId) return Result<BlogCategory>.NotFound();//没有找到
+
+    var validator = new BlogCategoryValidator();
+    var validation = await validator.ValidateAsync(blogCategory);
+    if (!validation.IsValid)
+    {
+        return Result<BlogCategory>.Invalid(validation.AsErrors());//验证异常
+    }
+
+    var itemToUpdate = (await GetByIdAsync(blogCategory.BlogCategoryId)).Value;
+    if (itemToUpdate == null)
+    {
+        return Result<BlogCategory>.NotFound();
+    }
+
+    itemToUpdate.Update(blogCategory.Name, blogCategory.ParentId);
+
+    return Result<BlogCategory>.Success(await _blogCategoryRepository.UpdateAsync(itemToUpdate));
+}
+```
+
+结果
+
+![ddd12](F:\SourceCodes\DDWiki\专题\后端\DDD\ddd12.png)
+
+# 接口
+
+```
+    [ApiController]
+    [Route("mediatr/[controller]")]
+    public class WeatherForecastController : ControllerBase
+    {
+        private readonly IMediator _mediator;
+        private readonly ILogger<WeatherForecastController> _logger;
+
+        public WeatherForecastController(
+            IMediator mediator,
+            ILogger<WeatherForecastController> logger)
+        {
+            _mediator = mediator;
+            _logger = logger;
+        }
+
+        /// <summary>
+        /// This uses a filter to convert an Ardalis.Result return type to an ActionResult.
+        /// This filter could be used per controller or globally!
+        /// </summary>
+        /// <param name="model"></param>
+        /// <returns></returns>
+        [TranslateResultToActionResult]//把Result的结果转换成ActionResult的结果，可以定义我们自己的特性，这点特别重要
+        [HttpPost("Create")]
+        public Task<Result<IEnumerable<WeatherForecast>>> CreateForecast([FromBody] NewForecastCommand model)
+        {
+            // One might try to perform translation from Result<T> to an appropriate IActionResult from within a MediatR pipeline
+            // Unfortunately without having Result<T> depend on IActionResult there doesn't appear to be a way to do this, so this
+            // example is still using the TranslateResultToActionResult filter.
+            return _mediator.Send(model);
+        }
+
+        public class NewForecastCommand : IRequest<Result<IEnumerable<WeatherForecast>>>
+        {
+            [Required]
+            public string PostalCode { get; set; }
+        }
+
+        public class NewForecastHandler : IRequestHandler<NewForecastCommand, Result<IEnumerable<WeatherForecast>>>
+        {
+            private readonly WeatherService _weatherService;
+
+            public NewForecastHandler(WeatherService weatherService)
+            {
+                _weatherService = weatherService;
+            }
+            public Task<Result<IEnumerable<WeatherForecast>>> Handle(NewForecastCommand request, CancellationToken cancellationToken)
+            {
+                var result = _weatherService.GetForecastAsync(new ForecastRequestDto { PostalCode = request.PostalCode });
+                return result;
+            }
+        }
+    }
+```
+
+在`WeatherService`中
+
+```
+    public class WeatherService
+    {
+        public WeatherService(IStringLocalizer<WeatherService> stringLocalizer)
+        {
+            _stringLocalizer = stringLocalizer;
+        }
+        private static readonly string[] Summaries = new[]
+{
+            "Freezing", "Bracing", "Chilly", "Cool", "Mild", "Warm", "Balmy", "Hot", "Sweltering", "Scorching"
+        };
+
+        private IStringLocalizer<WeatherService> _stringLocalizer;
+
+        public Task<Result<IEnumerable<WeatherForecast>>> GetForecastAsync(ForecastRequestDto model)
+        {
+            return Task.FromResult(GetForecast(model));
+        }
+
+        public Result<IEnumerable<WeatherForecast>> GetForecast(ForecastRequestDto model)
+        {
+            if (model.PostalCode == "NotFound") return Result<IEnumerable<WeatherForecast>>.NotFound();//没有找到
+
+            // validate model
+            if (model.PostalCode.Length > 10)
+            {
+                return Result<IEnumerable<WeatherForecast>>.Invalid(new List<ValidationError> {
+                    new ValidationError
+                    {
+                        Identifier = nameof(model.PostalCode),
+                        ErrorMessage = _stringLocalizer["PostalCode cannot exceed 10 characters."].Value }
+                });//模型验证失败
+            }
+
+            // test value
+            if (model.PostalCode == "55555")
+            {
+                return new Result<IEnumerable<WeatherForecast>>(Enumerable.Range(1, 1)//返回成功的结果
+                    .Select(index =>
+                    new WeatherForecast
+                    {
+                        Date = DateTime.Now,
+                        TemperatureC = 0,
+                        Summary = Summaries[0]
+                    }));
+            }
+
+            var rng = new Random();
+            return new Result<IEnumerable<WeatherForecast>>(Enumerable.Range(1, 5)//返回成功的结果
+                .Select(index => new WeatherForecast
+                {
+                    Date = DateTime.Now.AddDays(index),
+                    TemperatureC = rng.Next(-20, 55),
+                    Summary = Summaries[rng.Next(Summaries.Length)]
+                })
+            .ToArray());
+        }
+    }
+```
+
+如何影射`Result`结果呢？
+
+```
+   public class TranslateResultToActionResultAttribute : ActionFilterAttribute
+    {
+        public override void OnActionExecuted(ActionExecutedContext context)
+        {
+            if (!((context.Result as ObjectResult)?.Value is IResult result)) return;
+
+            if (!(context.Controller is ControllerBase controller)) return;
+
+			//判断IResult的ResultStatus
+            if (result.Status == ResultStatus.NotFound)
+                context.Result = controller.NotFound();
+
+            if (result.Status == ResultStatus.Invalid)
+            {
+                foreach (var error in result.ValidationErrors)
+                {
+                    // TODO: Fix after updating to 3.0.0
+                    (context.Controller as ControllerBase)?.ModelState.AddModelError(error.Identifier, error.ErrorMessage);
+                }
+
+                context.Result = controller.BadRequest(controller.ModelState);
+            }
+
+            if (result.Status == ResultStatus.Ok)
+            {
+                context.Result = new OkObjectResult(result.GetValue());
+            }
+        }
+    }
+```
+
+`IResult`
+
+```
+    public interface IResult
+    {
+        ResultStatus Status { get; }
+        IEnumerable<string> Errors { get; }
+        List<ValidationError> ValidationErrors { get; }
+        Type ValueType { get; }
+        Object GetValue();
+    }
+```
+
+`ResultStatus`
+
+```
+    public enum ResultStatus
+    {
+        Ok,
+        Error,
+        Forbidden,
+        Invalid,
+        NotFound
+    }
+```
+

决策/决策.md

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+> 购买云厂商MySql数据库
+
+决策：购买云厂商MySql数据库
+发起人：
+
+目前我们用的是自建MySQL服务器，好处是免费的，但是后期如果考虑维护性、安全性等方面的话，购买云厂商MySql数据库更合适。

团队/解决一次git问题.md

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+出现非常混乱的情况，首先本地回滚到某个版本：
+```
+git reset xxx --hard
+```
+然后让远程也回滚
+```
+git push origin master -f
+```