本文次要介绍了通过构造函数和畛域服务创立实体2种形式，后者多用于在创立实体时须要其它业务规定检测的场景。最初介绍了在应用服务层中如何进行实体的更新操作。
一.通过构造函数创立实体
如果Issue的聚合根类为：
public class Issue : AggregateRoot<Guid>{ public Guid RepositoryId { get; private set; } //不能批改RepositoryId，起因是不反对把一个Issue挪动到另外一个Repository上面 public string Title { get; private set; } //不能间接批改Title，能够通过SetTitle()批改，次要是在该办法中要退出对Title不能反复的校验 public string Text { get; set; } //能够间接批改 public Guid? AssignedUserId { get; internal set; } //同一个程序集中是能够批改AssignedUserId的 // 私有构造函数 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 } // 公有构造函数 private Issue() {} // 批改Title的办法 public void SetTitle(string title) { // Title不能反复 Title = Check.NotNullOrWhiteSpace(title, nameof(title)); } // ...}在应用服务层创立一个Issue的过程如下：
public class IssueAppService : ApplicationService.IIssueAppService{ private readonly IssueManager _issueManager; //Issue畛域服务 private readonly IRepository<Issue, Guid> _issueRepository; //Issue仓储 private readonly IRepository<AppUser, Guid> _userRepository; //User仓储 // 私有构造函数 public IssueAppService(IssueManager issueManager, IRepository<Issue, Guid> issueRepository, IRepository<AppUser, Guid> userRepository) { _issueManager = issueManager; _issueRepository = issueRepository; _userRepository = userRepository; } // 通过构造函数创立Issue public async Task<IssueDto> CreateAssync(IssueCreationDto input) { var issue = new Issue(GuidGenerator.Create(), input.RepositoryId, input.Title, input.Text); } if(input.AssigneeId.HasValue) { // 获取调配给Issue的User var user = await _userRepository.GetAsync(input.AssigneeId.Value); // 通过Issue的畛域服务，将Issue调配给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.通过畛域服务创立实体
什么样的状况下会用畛域服务创立实体，而不是通过实体构造函数来创立实体呢？次要用在创立实体时须要其它业务规定检测的场景。比方，在创立Issue的时候，不能创立Title雷同的Issue。通过Issue实体构造函数来创立Issue实体，这个是管制不住的。所以才会有通过畛域服务创立实体的状况。
阻止从Issue的构造函数来创立Issue实体，须要将其构造函数的拜访权限由public批改为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; //容许为空或者null } // ...}通过畛域服务IssueManager中的CreateAsync()办法来判断创立的Issue的Title是否反复：
public class IssueManager:DomainService{ private readonly IRepository<Issue,Guid> _issueRepository; // Issue的仓储 // 私有构造函数，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是否反复 if(await _issueRepository.AnyAsync(i=>i.Title==title)) { throw new BusinessException("IssueTracking:IssueWithSameTitleExists"); } // 返回创立的Issue实体 return new Issue(GuidGenerator.Create(), repositoryId, title, text); }}在应用服务层IssueAppService中通过IssueManager.CreateAsync()创立实体如下：
public class IssueAppService :ApplicationService.IIssueAppService{ private readonly IssueManager _issueManager; //Issue的畛域服务 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; } // 创立一个Issue public async Task<IssueDto> CreateAsync(IssueCreationDto input) { // 通过畛域服务的_issueManager.CreateAsync()创立实体，次要是保障Title不反复 var issue=await _issueManager.CreateAsync(input.RepositoryId, input.Title, input.Text); // 获取User，并将Issue调配给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的创立DTO为IssueCreationDtopublic class IssueCreationDto{ public Guid RepositoryId{get;set;} [Required] public string Title {get;set;} public Guid? AssignedUserId{get;set;} public string Text {get;set;}}当初有个疑难是为什么不把Title的反复检测放在畛域服务层中来做呢，这就波及一个辨别外围畛域逻辑还是应用逻辑的问题了。显然这里Title不能反复属于外围畛域逻辑，所以放在了畛域服务中来解决。为什么题目反复检测不在应⽤服务中实现？具体的解释参考[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()办法如下所示：
public class IssueAppService :ApplicationService.IIssueAppService{ private readonly IssueManager _issueManager; //Issue畛域服务 private readonly IRepository<Issue,Guid> _issueRepository; //Issue仓储 private readonly IRepository<AppUser,Guid> _userRepository; //User仓储 // 私有构造函数，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); // 通过畛域服务的issueManager.ChangeTitleAsync()办法更新Issue的题目 await _issueManager.ChangeTitleAsync(issue,input.Title); // 获取User，并将Issue调配给User if(input.AssignedUserId.HasValue) { var user = await _userRepository.GetAsync(input.AssignedUserId.Value); await _issueManager.AssignToAsync(issue, user); } issue.Text=input.Text; // 更新和保留Issue // 保留实体更改是应用服务办法的职责 await _issueRepository.UpdateAsync(issue); // 返回IssueDto return ObjectMapper.Map<Issue,IssueDto>(issue); }}须要在IssueManager中增加ChangeTitle()：
public async Task ChangeTitleAsync(Issue issue,string title){ // Title不变就返回 if(issue.Title==title) { return; } // Title反复就抛出异样 if(await _issueRepository.AnyAsync(i=>i.Title==title)) { throw new BusinessException("IssueTracking:IssueWithSameTitleExists"); } // 请它状况更新Title issue.SetTitle(title);}批改Issue类中SetTitle()办法的拜访权限为internal：
internal void SetTitle(string title){ Title=Check.NotNullOrWhiteSpace(title,nameof(title));}参考文献：
[1]基于ABP Framework实现畛域驱动设计：https://url39.ctfile.com/f/25... (拜访明码: 2096)
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