Aggregate root design and presentation layer

Question

I was wondering if how my presentation layer is structured could be a lead to design my aggregate roots.

Lets have an entity ProjectEntity and its related entity ProjectMemberEntity (1:M)

The page is structured as follows:

The top of the page is a form for ProjectEntity

Underneath the form is a grid that shows a list of ProjectMemberEntity.

If a new ProjectMember will be added, the user have to go to this page and click on the button "add new member" which is located in the header of the grid.also edit and delete has the same analogy.

I'm wondering if this behavior/'page structure' could be a hint for a aggregate root(projectentity)

Answer 1

That's a hint for sure. But no more.

Better way to clarify kind of that entity relationship is to ask domain expert:

• does project member makes any sense without project?
• can member participate in multiple projects?

If those are answered positively, it's highly likely that You should model project member as an aggregate root itself. Otherwise - demote it as an entity that cannot live w/o a project.

---

Here is some code that might give You some ideas:

public class Project:Root{
 private List _members;
 public IEnumerable<Member> Members{get {return _members;}}
 public string Name{get;private set;}
 public bool IsFinished{get;private set;}
 public bool FinishedOn{get;private set;}
 public Project(string projectName){
  _members=new List<Member>();
  Name=projectName;
 }
 public Member AssignMember(string memberName){
  var member=new Member(memberName);
  _members.Add(member);
  return member;
 }
 public void UnassignMember(string memberName){
  var member=_members.First(m=>m.Name==memberName);
  if(!member.HasCompletedAllTasks())
   throw new Exception
    ("Cannot unassign member with incompleted tasks!");
  _members.Remove(member);
 }
 public void AssignTaskToMember(string taskName, string memberName){
  var member=_members.First(m=>m.Name==memberName);
  member.AssignTask(taskName);
 }
 public void MemberHasCompletedTask(Member member, Task task){
  EnsureListContains(_members,member);
  EnsureListContains(member.Tasks,task);
  task.MarkAsCompleted();
 }    
 public void FinishProject(){
  if(_members.Any(m=>!m.HasCompletedAllTasks()))
   throw new Exception
    ("Can't finish project before members have completed all their tasks.");
  IsFinished=true;
  FinishedOn=DateTime.Now;
 }
 private void EnsureListContains<T>(IList<T> lst, T itm){
  if(!lst.Contains(itm)) throw new Exception();
 }
}

public class Member:Entity{
 public string Name{get;private set;}
 private List<Task> _tasks;
 public IEnumerable<Task> Tasks{get{return _tasks;}}
 internal Member(string memberName){
  Name=name;
  _tasks=new List<Task>();
 }
 internal void AssignTask(string taskName){
  _tasks.Add(new Task(taskName));
 }
 public bool HasCompletedAllTasks(){
  return _tasks.All(t=>t.IsCompleted);
 }
 public Task GetNextAssignedTask(){
  return _tasks.Where(t=>!t.IsCompleted)
    .OrderBy(t=>t.AssignedOn).First();
 }
}

public class Task:Entity{
 public string Name{get; private set;}
 public bool IsCompleted{get; private set;}
 public DateTime CompletedOn{get; private set;}    
 public DateTime AssignedOn{get; private set;}
 internal Task(string name){
  Name=name;
  AssignedOn=DateTime.Now;
 }
 internal void MarkAsCompleted(){
  if(IsCompleted) throw new Exception
   ("Task is already completed!");
  IsCompleted=true;
  CompletedOn=DateTime.Now;
 }
}

public class App{
 public static void Main(){
  var project=new Project
    ("Question: Aggregate root design and presentation layer");
  var me=project.AssignMember("Arnis Lapsa");
  project.AssignTaskToMember("Try to help user137348","Lapsa");
  var currentTask=me.GetNextAssignedTask();
  //SpamStackOverflow();
  project.MemberHasCompletedTask(me,currentTask);
  if(me.HasCompletedAllTasks()) project.Finish();
  else throw new Exception("Enough for today...");
 }
}

Keep in mind that I got little knowledge of what Your business is about. This is just an improvisation. :)

Answer 2

When it comes to DDD, make sure you don't get analysis paralysis when trying to design your domain and aggregates. It happened to me. My project got literally STOPPED for a whole month because i wasn't enable to get my aggregates straight. And i am talking about a simple 3 database tables situation. User, Address and UserProfile.

The thing with DDD is that there is no such a thing like DONE THE RIGHT WAY. If you post the same question here with an interval of 3 months from each other, you will always get the "experts" giving you completely different answers in each question. Amis L. was kind enough to give you a solid simple example. Most people would copy and paste from Eric's books.

Do whatever floats your boat. At the end of the day, no matter how handcrafted your domain is, it's never RIGHT to the community. Just chill and enjoy coding.