Store a hierarchy and return all children

Q: Store a hierarchy and return all children

This question evaluates understanding of hierarchical data modeling, REST API design, database schema choices (e.g., adjacency list vs alternatives), and systems-level concerns like scalability, pagination for large subtrees, and cycle prevention.

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Question

Design a service to store a hierarchical tree of nodes and expose APIs.

Requirements:

Persist a hierarchy (a forest with multiple roots is acceptable).
Support:
1. Add a node under a parent.
2. Return all descendants (all children recursively) of a given node.
Emphasis on REST API design, DB schema, and edge cases.

Deliverables:

API endpoints and example requests/responses.
Storage model choice (e.g., adjacency list, materialized path, nested sets, closure table) and justification.
How to handle large subtrees (pagination) and prevent cycles.

Store a hierarchy and return all children

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