我的NopCommerce之旅(4): 定时任务之邮件

一、功能简介

用户购买物品生成订单后，系统将发送邮件提醒给用户

二、操作步骤

1. 后台配置一个系统的默认发送邮箱
   
2. 启动定时任务，这里包括多个任务，只需要启动邮件任务
   
3. 查看邮件发送情况
   

三、数据库分析

1. [dbo].[Log] 系统日志表，可查看邮件发送失败的异常信息
2. [dbo].[EmailAccount] 系统发送邮件配置表
3. [dbo].[QueuedEmail] 订单邮件序列表，[SentTries]为重试次数，默认尝试3次失败后不再发送。
4. [dbo].[ScheduleTask] 定时任务信息表，存储定时任务信息。

四、源码解析

1. 根据MVC命名规则，可定位到Nop.Admin.Controllers命名空间，
2. 查看ScheduleTaskController的RunNow方法，可跟踪查看到任务调用机制。
   1. 通过反射类型，采用autofac实例化对象，然后执行。
   2. 任务实现Nop.Services.Tasks.ITask接口的Execute()方法，如Nop.Services.Messages.QueuedMessagesSendTask。

         private ITask CreateTask(ILifetimeScope scope)
         {
             ITask task = null;
             if (this.Enabled)
             {
                 var type2 = System.Type.GetType(this.Type);
                 if (type2 != null)
                 {
                     object instance;
                     if (!EngineContext.Current.ContainerManager.TryResolve(type2, scope, out instance))
                     {
                         //not resolved
                         instance = EngineContext.Current.ContainerManager.ResolveUnregistered(type2, scope);
                     }
                     task = instance as ITask;
                 }
             }
             return task;
         }

         /// <summary>
         /// Executes the task
         /// </summary>
         /// <param name="throwException">A value indicating whether exception should be thrown if some error happens</param>
         /// <param name="dispose">A value indicating whether all instances should be disposed after task run</param>
         /// <param name="ensureRunOnOneWebFarmInstance">A value indicating whether we should ensure this task is run on one farm node at a time</param>
         public void Execute(bool throwException = false, bool dispose = true, bool ensureRunOnOneWebFarmInstance = true)
         {
             ...
                 //initialize and execute 初始化成功后执行任务
                 var task = this.CreateTask(scope);
                 if (task != null)
                 {
                     this.LastStartUtc = DateTime.UtcNow;
                     if (scheduleTask != null)
                     {
                         //update appropriate datetime properties
                         scheduleTask.LastStartUtc = this.LastStartUtc;
                         scheduleTaskService.UpdateTask(scheduleTask);
                     }
                     task.Execute();
                     this.LastEndUtc = this.LastSuccessUtc = DateTime.UtcNow;
                 }
             }
             catch (Exception exc)
             {
                 this.Enabled = !this.StopOnError;
                 this.LastEndUtc = DateTime.UtcNow;

                 //log error
                 var logger = EngineContext.Current.ContainerManager.Resolve<ILogger>("", scope);
                 logger.Error(string.Format("Error while running the '{0}' schedule task. {1}", this.Name, exc.Message), exc);
                 if (throwException)
                     throw;
             }

             if (scheduleTask != null)
             {
                 //update appropriate datetime properties
                 scheduleTask.LastEndUtc = this.LastEndUtc;
                 scheduleTask.LastSuccessUtc = this.LastSuccessUtc;
                 scheduleTaskService.UpdateTask(scheduleTask);
             }

             //dispose all resources
             if (dispose)
             {
                 scope.Dispose();
             }
         }

五、技术解析

1. Autofac的依赖注入
2. 反射