AggregateRoot should support recursive data structures (Composite Component pattern) #24
Description
The support for nesting Components and Entities within an Aggregate is currently more limited than it should be. It locks the structure down to a specific depth of nesting where the exact type is known at each depth.
This is unacceptably limiting. We should support more dynamic nesting strategies.
- Recursive data structure. (Composite Component)
- Unknown subtype at each nesting level. (BranchType1, BranchType2, LeafType1)
Implement example of this Aggregate in the Samples project: Thread/Post Composite Aggregate where the Aggregate is a thread with a name and a root Post that is a recursive structure where each post contains a list of Answers that are also Posts.
Early Solution draft
- RecursiveEntityCollectionManager generic class that adds the ability to handle recursive structures.
- Type parameter TParentEntityIdGetter
- Optional Type parameter TInstanceFactory that specifies a factory class to use for creating the correct subtype of the nested entity.
Questions
- How do you handle the case where the root is a single object instead of a collection? Such as the Post case that would be used in the sample? Currently entity and nested entity require a collection to work. Would it be OK to simple keep this restriction and leave it up to the implementation of the Aggregate/Entity to ensure that no more root level entities are added?.