应用服务用于将领域(业务)逻辑暴露给展现层。展现层通过传入DTO(数据传输对象)参数来调用应用服务，而应用服务通过领域对象来执行相应的业务逻辑并且将DTO返回给展现层。因此，展现层和领域层将被完全隔离开来。
以下几点，在创建应用服务时需要注意：
IApplicationService接口，最好的实践是针对每个应用服务都创建相应继承自IApplicationService的接口。（通过继承该接口，ABP会自动帮助依赖注入）
IApplicationService提供了默认的实现ApplicationService，该基类提供了方便的日志记录和本地化功能。实现应用服务的时候继承自ApplicationService并实现定义的接口即可。
public interface ITaskAppService : IApplicationService
{
GetTasksOutput GetTasks(GetTasksInput input);
void UpdateTask(UpdateTaskInput input);
int CreateTask(CreateTaskInput input);
Task<TaskDto> GetTaskByIdAsync(int taskId);
TaskDto GetTaskById(int taskId);
void DeleteTask(int taskId);
IList<TaskDto> GetAllTasks();
}观察方法的参数及返回值，大家可能会发现并未直接使用Task实体对象。这是为什么呢？因为展现层与应用服务层是通过Data Transfer Object（DTO）进行数据传输。
总结来说，使用DTO进行数据传输具有以下好处。
了解更多详情请参考：
ABP框架 - 数据传输对象
namespace LearningMpaAbp.Tasks.Dtos
{
/// <summary>
/// A DTO class that can be used in various application service methods when needed to send/receive Task objects.
/// </summary>
public class TaskDto : EntityDto
{
public long? AssignedPersonId { get; set; }
public string AssignedPersonName { get; set; }
public string Title { get; set; }
public string Description { get; set; }
public DateTime CreationTime { get; set; }
public TaskState State { get; set; }
//This method is just used by the Console Application to list tasks
public override string ToString()
{
return string.Format(
"[Task Id={0}, Description={1}, CreationTime={2}, AssignedPersonName={3}, State={4}]",
Id,
Description,
CreationTime,
AssignedPersonId,
(TaskState)State
);
}
}
}
该TaskDto直接继承自EntityDto，EntityDto是一个通用的实体只定义Id属性的简单类。直接定义一个TaskDto的目的是为了在多个应用服务方法中共用。
就是直接共用了TaskDto。
public class GetTasksOutput
{
public List<TaskDto> Tasks { get; set; }
} public class CreateTaskInput
{
public int? AssignedPersonId { get; set; }
[Required]
public string Description { get; set; }
[Required]
public string Title { get; set; }
public TaskState State { get; set; }
public override string ToString()
{
return string.Format("[CreateTaskInput > AssignedPersonId = {0}, Description = {1}]", AssignedPersonId, Description);
}
} /// <summary>
/// This DTO class is used to send needed data to <see cref="ITaskAppService.UpdateTask"/> method.
///
/// Implements <see cref="ICustomValidate"/> for additional custom validation.
/// </summary>
public class UpdateTaskInput : ICustomValidate
{
[Range(1, Int32.MaxValue)] //Data annotation attributes work as expected.
public int Id { get; set; }
public int? AssignedPersonId { get; set; }
public TaskState? State { get; set; }
[Required]
public string Title { get; set; }
[Required]
public string Description { get; set; }
//Custom validation method. It's called by ABP after data annotation validations.
public void AddValidationErrors(CustomValidationContext context)
{
if (AssignedPersonId == null && State == null)
{
context.Results.Add(new ValidationResult("Both of AssignedPersonId and State can not be null in order to update a Task!", new[] { "AssignedPersonId", "State" }));
}
}
public override string ToString()
{
return string.Format("[UpdateTaskInput > TaskId = {0}, AssignedPersonId = {1}, State = {2}]", Id, AssignedPersonId, State);
}
}
其中UpdateTaskInput实现了ICustomValidate接口，来实现自定义验证。了解DTO验证可参考 ABP框架 - 验证数据传输对象
其中包括两个属性用来进行过滤。
public class GetTasksInput
{
public TaskState? State { get; set; }
public int? AssignedPersonId { get; set; }
}
定义完DTO，是不是脑袋有个疑问，我在用DTO在展现层与应用服务层进行数据传输，但最终这些DTO都需要转换为实体才能与数据库直接打交道啊。如果每个dto都要自己手动去转换成对应实体，这个工作量也是不可小觑啊。
聪明如你，你肯定会想肯定有什么方法来减少这个工作量。
开始之前，如果对AutoMapper不是很了解，建议看下这篇文章AutoMapper小结。
AutoMapper的使用步骤，简单总结下：
Mapper.CreateMap<source, destination>();）
Mapper.Map<source,destination>(sourceModel)）
在Abp中有两种方式创建映射规则：
Mapper.CreateMap<source, destination>();
CreateTasksInput、UpdateTaskInput中的属性名与Task实体的属性命名一致，且只需要从Dto映射到实体，不需要反向映射。所以通过AutoMapTo创建单向映射即可。
[AutoMapTo(typeof(Task))] //定义单向映射
public class CreateTaskInput
{
...
}
[AutoMapTo(typeof(Task))] //定义单向映射
public class UpdateTaskInput
{
...
}
`
TaskDto与Task实体的属性中，有一个属性名不匹配。TaskDto中的AssignedPersonName属性对应的是Task实体中的AssignedPerson.FullName属性。针对这一属性映射，AutoMapper没有这么智能需要我们告诉它怎么做；
var taskDtoMapper = mapperConfig.CreateMap<Task, TaskDto>();
taskDtoMapper.ForMember(dto => dto.AssignedPersonName, map => map.MapFrom(m => m.AssignedPerson.FullName));
为TaskDto与Task创建完自定义映射规则后，我们需要思考，这段代码该放在什么地方呢？
如果在映射规则既有通过特性方式又有通过代码方式创建，这时就会容易混乱不便维护。
为了解决这个问题，统一采用代码创建映射规则的方式。并通过IOC容器注册所有的映射规则类，再循环调用注册方法。
应用服务层根目录创建IDtoMapping接口，定义CreateMapping方法由映射规则类实现。
namespace LearningMpaAbp
{
/// <summary>
/// 实现该接口以进行映射规则创建
/// </summary>
internal interface IDtoMapping
{
void CreateMapping(IMapperConfigurationExpression mapperConfig);
}
}namespace LearningMpaAbp.Tasks
{
public class TaskDtoMapping : IDtoMapping
{
public void CreateMapping(IMapperConfigurationExpression mapperConfig)
{
//定义单向映射
mapperConfig.CreateMap<CreateTaskInput, Task>();
mapperConfig.CreateMap<UpdateTaskInput, Task>();
mapperConfig.CreateMap<TaskDto, UpdateTaskInput>();
//自定义映射
var taskDtoMapper = mapperConfig.CreateMap<Task, TaskDto>();
taskDtoMapper.ForMember(dto => dto.AssignedPersonName, map => map.MapFrom(m => m.AssignedPerson.FullName));
}
}
}
在应用服务的模块中对IDtoMapping进行依赖注册，并解析以进行映射规则创建。
namespace LearningMpaAbp
{
[DependsOn(typeof(LearningMpaAbpCoreModule), typeof(AbpAutoMapperModule))]
public class LearningMpaAbpApplicationModule : AbpModule
{
public override void PreInitialize()
{
Configuration.Modules.AbpAutoMapper().Configurators.Add(mapper =>
{
//Add your custom AutoMapper mappings here...
});
}
public override void Initialize()
{
IocManager.RegisterAssemblyByConvention(Assembly.GetExecutingAssembly());
//注册IDtoMapping
IocManager.IocContainer.Register(
Classes.FromAssembly(Assembly.GetExecutingAssembly())
.IncludeNonPublicTypes()
.BasedOn<IDtoMapping>()
.WithService.Self()
.WithService.DefaultInterfaces()
.LifestyleTransient()
);
//解析依赖，并进行映射规则创建
Configuration.Modules.AbpAutoMapper().Configurators.Add(mapper =>
{
var mappers = IocManager.IocContainer.ResolveAll<IDtoMapping>();
foreach (var dtomap in mappers)
dtomap.CreateMapping(mapper);
});
}
}
}
通过这种方式，我们只需要实现IDtoMappting进行映射规则定义。创建映射规则的动作就交给模块吧。
认真读完以上内容，那么到这一步，就很简单了，业务只是简单的增删该查，实现起来就很简单了。可以自己尝试自行实现，再参考代码：
namespace LearningMpaAbp.Tasks
{
/// <summary>
/// Implements <see cref="ITaskAppService"/> to perform task related application functionality.
///
/// Inherits from <see cref="ApplicationService"/>.
/// <see cref="ApplicationService"/> contains some basic functionality common for application services (such as logging and localization).
/// </summary>
public class TaskAppService : LearningMpaAbpAppServiceBase, ITaskAppService
{
//These members set in constructor using constructor injection.
private readonly IRepository<Task> _taskRepository;
/// <summary>
///In constructor, we can get needed classes/interfaces.
///They are sent here by dependency injection system automatically.
/// </summary>
public TaskAppService(IRepository<Task> taskRepository,)
{
_taskRepository = taskRepository;
}
public GetTasksOutput GetTasks(GetTasksInput input)
{
var query = _taskRepository.GetAll();
if (input.AssignedPersonId.HasValue)
{
query = query.Where(t => t.AssignedPersonId == input.AssignedPersonId.Value);
}
if (input.State.HasValue)
{
query = query.Where(t => t.State == input.State.Value);
}
//Used AutoMapper to automatically convert List<Task> to List<TaskDto>.
return new GetTasksOutput
{
Tasks = Mapper.Map<List<TaskDto>>(query.ToList())
};
}
public async Task<TaskDto> GetTaskByIdAsync(int taskId)
{
//Called specific GetAllWithPeople method of task repository.
var task = await _taskRepository.GetAsync(taskId);
//Used AutoMapper to automatically convert List<Task> to List<TaskDto>.
return task.MapTo<TaskDto>();
}
public TaskDto GetTaskById(int taskId)
{
var task = _taskRepository.Get(taskId);
return task.MapTo<TaskDto>();
}
public void UpdateTask(UpdateTaskInput input)
{
//We can use Logger, it's defined in ApplicationService base class.
Logger.Info("Updating a task for input: " + input);
//Retrieving a task entity with given id using standard Get method of repositories.
var task = _taskRepository.Get(input.Id);
//Updating changed properties of the retrieved task entity.
if (input.State.HasValue)
{
task.State = input.State.Value;
}
//We even do not call Update method of the repository.
//Because an application service method is a 'unit of work' scope as default.
//ABP automatically saves all changes when a 'unit of work' scope ends (without any exception).
}
public int CreateTask(CreateTaskInput input)
{
//We can use Logger, it's defined in ApplicationService class.
Logger.Info("Creating a task for input: " + input);
//Creating a new Task entity with given input's properties
var task = new Task
{
Description = input.Description,
Title = input.Title,
State = input.State,
CreationTime = Clock.Now
};
//Saving entity with standard Insert method of repositories.
return _taskRepository.InsertAndGetId(task);
}
public void DeleteTask(int taskId)
{
var task = _taskRepository.Get(taskId);
if (task != null)
{
_taskRepository.Delete(task);
}
}
}
}到此，此章节就告一段落。为了加深印象，请自行回答如下问题：
源码已上传至Github-LearningMpaAbp，可自行参考。