一.通过构造函数创建实体
假如Issue的聚合根类为：
public class Issue : AggregateRoot<Guid>
{
public Guid RepositoryId { get; private set; } //不能修改RepositoryId，原因是不支持把一个Issue移动到另外一个Repository下面
public string Title { get; private set; } //不能直接修改Title，可以通过SetTitle()修改，主要是在该方法中要加入对Title不能重复的校验
public string Text { get; set; } //可以直接修改
public Guid? AssignedUserId { get; internal set; } //同一个程序集中是可以修改AssignedUserId的
// 公有构造函数
public Issue(Guid id, Guid repositoryId, string title, string text=null) : base(id)
{
RepositoryId = repositoryId;
Title = Check.NotNullOrWhiteSpace(title, nameof(title));
Text = text; //可为空或者null
}
// 私有构造函数
private Issue() {}
// 修改Title的方法
public void SetTitle(string title)
{
// Title不能重复
Title = Check.NotNullOrWhiteSpace(title, nameof(title));
}
// ...
}
在应用服务层创建一个Issue的过程如下：
public class IssueAppService : ApplicationService.IIssueAppService
{
private readonly IssueManager _issueManager; //Issue领域服务
private readonly IRepository<Issue, Guid> _issueRepository; //Issue仓储
private readonly IRepository<AppUser, Guid> _userRepository; //User仓储
// 公有构造函数
public IssueAppService(IssueManager issueManager, IRepository<Issue, Guid> issueRepository, IRepository<AppUser, Guid> userRepository)
{
_issueManager = issueManager;
_issueRepository = issueRepository;
_userRepository = userRepository;
}
// 通过构造函数创建Issue
public async Task<IssueDto> CreateAssync(IssueCreationDto input)
{
var issue = new Issue(GuidGenerator.Create(), input.RepositoryId, input.Title, input.Text);
}
if(input.AssigneeId.HasValue)
{
// 获取分配给Issue的User
var user = await _userRepository.GetAsync(input.AssigneeId.Value);
// 通过Issue的领域服务，将Issue分配给User
await _issueManager.AssignAsync(issue, user);
}
// 插入和更新Issue
await _issueRepository.InsertAsync(issue);
// 返回IssueDto
return ObjectMapper.Map<Issue, IssueDto>(issue);
}
二.通过领域服务创建实体
什么样的情况下会用领域服务创建实体，而不是通过实体构造函数来创建实体呢？主要用在创建实体时需要其它业务规则检测的场景。比如，在创建Issue的时候，不能创建Title相同的Issue。通过Issue实体构造函数来创建Issue实体，这个是控制不住的。所以才会有通过领域服务创建实体的情况。
阻止从Issue的构造函数来创建Issue实体，需要将其构造函数的访问权限由public修改为internal：
public class Issue : AggregateRoot<Guid>
{
// ...
internal Issue(Guid id, Guid repositoryId, string title, string text = null) : base(id)
{
RepositoryId = repositoryId;
Title = Check.NotNullOrEmpty(title, nameof(title));
Text = text; //允许为空或者null
}
// ...
}
通过领域服务IssueManager中的CreateAsync()方法来判断创建的Issue的Title是否重复：
public class IssueManager:DomainService
{
private readonly IRepository<Issue,Guid> _issueRepository; // Issue的仓储
// 公有构造函数，注入仓储
public IssueManager(IRepository<Issue,Guid> issueRepository)
{
_issueRepository=issueRepository;
}
public async Task<Issue> CreateAsync(Guid repositoryId, string title, string text=null)
{
// 判断Issue的Title是否重复
if(await _issueRepository.AnyAsync(i=>i.Title==title))
{
throw new BusinessException("IssueTracking:IssueWithSameTitleExists");
}
// 返回创建的Issue实体
return new Issue(GuidGenerator.Create(), repositoryId, title, text);
}
}
在应用服务层IssueAppService中通过IssueManager.CreateAsync()创建实体如下：
public class IssueAppService :ApplicationService.IIssueAppService
{
private readonly IssueManager _issueManager; //Issue的领域服务
private readonly IRepository<Issue,Guid> _issueRepository; //Issue的仓储
private readonly IRepository<AppUser,Guid> _userRepository; //User的仓储
// 公共的构造函数，注入所需的依赖
public IssueAppService(IssueManager issueManager, IRepository<Issue,Guid> issueRepository, IRepository<AppUser,Guid> userRepository){
_issueManager=issueManager;
_issueRepository=issueRepository;
_userRepository=userRepository;
}
// 创建一个Issue
public async Task<IssueDto> CreateAsync(IssueCreationDto input)
{
// 通过领域服务的_issueManager.CreateAsync()创建实体，主要是保证Title不重复
var issue=await _issueManager.CreateAsync(input.RepositoryId, input.Title, input.Text);
// 获取User，并将Issue分配给User
if(input.AssignedUserId.HasValue)
{
var user =await _userRepository.GetAsync(input.AssignedUserId.Value);
await _issueManager.AssignToAsynce(issue,user);
}
// 插入和更新数据库
await _issueRepository.InsertAsync(issue);
// 返回IssueDto
return ObjectMapper.Map<Issue,IssueDto>(issue);
}
}
// 定义Issue的创建DTO为IssueCreationDto
public class IssueCreationDto
{
public Guid RepositoryId{get;set;}
[Required]
public string Title {get;set;}
public Guid? AssignedUserId{get;set;}
public string Text {get;set;}
}
现在有个疑问是为什么不把Title的重复检测放在领域服务层中来做呢，这就涉及一个区分核心领域逻辑还是应用逻辑的问题了。显然这里Title不能重复属于核心领域逻辑，所以放在了领域服务中来处理。为什么标题重复检测不在应⽤服务中实现？详细的解释参考[1]。
三.实体的更新操作
接下来介绍在应用层IssueAppService中来update实体。定义UpdateIssueDto如下：
public class UpdateIssueDto
{
[Required]
public string Title {get;set;}
public string Text{get;set;}
public Guid? AssignedUserId{get;set;}
}
实体更新操作的UpdateAsync()方法如下所示：
public class IssueAppService :ApplicationService.IIssueAppService
{
private readonly IssueManager _issueManager; //Issue领域服务
private readonly IRepository<Issue,Guid> _issueRepository; //Issue仓储
private readonly IRepository<AppUser,Guid> _userRepository; //User仓储
// 公有构造函数，注入依赖
public IssueAppService(IssueManager issueManager, IRepository<Issue,Guid> issueRepository, IRepository<AppUser,Guid> userRepository){
_issueManager=issueManager;
_issueRepository=issueRepository;
_userRepository=userRepository;
}
// 更新Issue
public async Task<IssueDto> UpdateAsync(Guid id, UpdateIssueDto input)
{
// 从Issue仓储中获取Issue实体
var issue = await _issueRepository.GetAsync(id);
// 通过领域服务的issueManager.ChangeTitleAsync()方法更新Issue的标题
await _issueManager.ChangeTitleAsync(issue,input.Title);
// 获取User，并将Issue分配给User
if(input.AssignedUserId.HasValue)
{
var user = await _userRepository.GetAsync(input.AssignedUserId.Value);
await _issueManager.AssignToAsync(issue, user);
}
issue.Text=input.Text;
// 更新和保存Issue
// 保存实体更改是应用服务方法的职责
await _issueRepository.UpdateAsync(issue);
// 返回IssueDto
return ObjectMapper.Map<Issue,IssueDto>(issue);
}
}
需要在IssueManager中添加ChangeTitle()：
public async Task ChangeTitleAsync(Issue issue,string title)
{
// Title不变就返回
if(issue.Title==title)
{
return;
}
// Title重复就抛出异常
if(await _issueRepository.AnyAsync(i=>i.Title==title))
{
throw new BusinessException("IssueTracking:IssueWithSameTitleExists");
}
// 请它情况更新Title
issue.SetTitle(title);
}
修改Issue类中SetTitle()方法的访问权限为internal：
internal void SetTitle(string title)
{
Title=Check.NotNullOrWhiteSpace(title,nameof(title));
}
