一个聚合根可以引用另一个聚合根的非聚合根吗？

Question

I have three entities for this particular scenario:

• Question (aggregate root)
• QuestionFeedback (not aggregate root)
• QuestionFeedbackCategory (aggregate root)

Since QuestionFeedback is inside a Question, can QuestionFeedbackCategory hold a list of QuestionFeedback objects too? Or does QuestionFeedbackCategory need to deal only with Question objects?

Answer 1

If both Question and QuestionFeedback have Categories and assuming each can only have one category, I would model it this way

public class Question {
    ...
    CategoryId categoryId;
    Set<QuestionFeedback> feedback;
    ...
} 

public class QuestionFeedback {
    ...
    CategoryId categoryId;
    ...
} 

public class Category {
    CategoryId id;
    String name;
    String description;
}

You don't have to put the AR itself "inside" another AR/VO. You can just reference its Value Object that acts as the id.

Edit: Read the three part article mentioned here http://dddcommunity.org/library/vernon_2011 . Coming from an ORM mindset, I used to get confused on how to model these types of relationships.

Answer 2

The aggregate root can communicate with the outside only in these scenarios:

• via events inside aggregate
• injection via constructor

but in all above options, no reference is allowed only array(the hydrated object) can be used.