在这篇文章中使用Vaughn Vernon的书[ IDDD，2013 ] 的例子来描述SCRUM模型的情景，并能够以实际的方式展示贫血模型和富模型的实现之间的区别。
让我们说产品负责人：
允许将每个积压项分配给Sprint。如果它已经分配给不同的Sprint，则必须先将其解除分配。分配完成后，通知相关方。
一个非常简单的场景，可以在下面分层显示：
尽管在图中有表示，但我们将在示例中忽略Task。
贫血模型
领域/实体
public class Sprint
{
public int Id { get; set; }
public IList<BacklogItem> BacklogItems { get; set; }
public SprintStatusEnum Status { get; set; }
public string Description { get; set; }
public DateTime BeginDate { get; set; }
public DateTime EndDate { get; set; }
}
public class BacklogItem
{
public int Id { get; set; }
public IList<Task> Tasks { get; set; }
public int? SprintId { get; set; }
public int? UserId { get; set; }
public BacklogItemStatusEnum Status { get; set; }
public string Description { get; set; }
public DateTime? BeginDate { get; set; }
public DateTime? EndDate { get; set; }
}
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领域/服务
public class SprintServices : ISprintServices
{
private readonly ISprintRepository _sprintRepository;
private readonly IBacklogItemRepository _backlogItemRepository;
public SprintServices(ISprintRepository sprintRepository, IBacklogItemRepository backlogItemRepository)
{
_sprintRepository = sprintRepository;
_backlogItemRepository = backlogItemRepository;
}
public void InsertBacklogItem(int sprintId, int backLogItemId)
{
var sprint = _sprintRepository.GetById(sprintId);
var backLogItem = _backlogItemRepository.GetById(backLogItemId);
backLogItem.SprintId = sprintId;
backLogItem.Status = BacklogItemStatusEnum.Committed;
EmailService.SendMail("destination@email.com",
$"The backlog item '{backLogItem.Description}' was assigned to Sprint '{sprint.Description}'");
_backlogItemRepository.Update(backLogItem);
}
}
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请注意，它们的实体没有业务逻辑，每个规则都依赖领域服务，实体属性设置没有任何控制，设置这些属性后没有验证，聚合不生成域事件。
这样的对象只是数据容器。
现在看看富血模型......
域/实体
public class Sprint : Entity
{
public Sprint(string description, DateTime beginDate, DateTime endDate)
{
Status = SprintStatusEnum.New;
Description = description;
BeginDate = beginDate;
EndDate = endDate;
Validate();
}
public int Id { get; private set; }
public IList<BacklogItem> BacklogItems { get; private set; }
public SprintStatusEnum Status { get; private set; }
public string Description { get; private set; }
public DateTime BeginDate { get; private set; }
public DateTime EndDate { get; private set; }
public void SetStatus(SprintStatusEnum status) => Status = status;
public void SetDescription(string description) => Description = description;
public void SetBeginDate(DateTime beginDate) => BeginDate = beginDate;
public void SetEndDate(DateTime endDate) => BeginDate = endDate;
public void Validate()
{
if (string.IsNullOrEmpty(Description))
{
throw new Exception("Description can not be null");
}
if (BeginDate > EndDate)
{
throw new Exception("EndDate must be greater than BeginDate");
}
//more rules...
}
}
public class BacklogItem : Entity
{
public BacklogItem(string description)
{
Status = BacklogItemStatusEnum.New;
Description = description;
Validate();
}
public int Id { get; private set; }
public IList<Task> Tasks { get; private set; }
public int? SprintId { get; private set; }
public int? UserId { get; private set; }
public BacklogItemStatusEnum Status { get; private set; }
public string Description { get; private set; }
public DateTime? BeginDate { get; private set; }
public DateTime? EndDate { get; private set; }
public void SetSprintId(int? sprintId) => SprintId = sprintId;
public void SetUserId(int? userId) => UserId = userId;
public void SetStatusToNew() => Status = BacklogItemStatusEnum.New;
public void SetStatusToCommitted() => Status = BacklogItemStatusEnum.Committed;
public void SetStatusToApproved() => Status = BacklogItemStatusEnum.Approved;
public void SetStatusToDone() => Status = BacklogItemStatusEnum.Done;
public void SetDescription(string description) => Description = description;
public void SetBeginDate(DateTime? beginDate) => BeginDate = beginDate;
public void SetEndDate(DateTime? endDate) => BeginDate = endDate;
public void CommitToSprint(Sprint sprint)
{
if (IsCommittedToSprint())
{
UncommitFromSprint();
}
SetStatusToCommitted();
SetSprintId(sprint.Id);
this.AddDomainEvent(new BacklogItemCommitted
{
Id = Id,
SprintId = SprintId.Value
});
}
public void UncommitFromSprint()
{
SprintId = null;
this.AddDomainEvent(new BacklogItemUncommitFromSprint
{
Id = Id,
SprintId = SprintId.Value
});
}
public bool IsCommittedToSprint() => SprintId != null && SprintId != default(int);
public void Validate()
{
if (string.IsNullOrEmpty(Description))
{
throw new Exception("Description can not be null");
}
//more rules...
}
}
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应用：
public class BoardApplication : IBoardApplication
{
private readonly ISprintRepository _sprintRepository;
private readonly IBacklogItemRepository _backlogItemRepository;
public BoardApplication(ISprintRepository sprintRepository, IBacklogItemRepository backlogItemRepository)
{
_sprintRepository = sprintRepository;
_backlogItemRepository = backlogItemRepository;
}
public void ToAllocateBacklogItemToaSprint(int sprintId, int backLogItemId)
{
var sprint = _sprintRepository.GetById(sprintId);
var backLogItem = _backlogItemRepository.GetById(backLogItemId);
backLogItem.CommitToSprint(sprint);
_backlogItemRepository.Update(backLogItem);
}
}
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你能看到区别么？
第一个例子使用了一种非常以数据为中心的方法，而不是行为方法。它不是一个真正的领域模型。
在我们的Rich Model示例中，我们使用表达泛在语言的域对象的行为。
它不会向客户端公开数据属性，而是公开一种行为，该行为明确且清楚地表明客户可以将Backlog项目分配给Sprint。
如果不将此丰富的行为插入Backlog项，则客户端必须处理事件，这是非常错误的。
在第二个例子中，好处要大得多。
现在，您能看到使用Rich Model的好处吗？