Database Schema Changelog

v1.1.0 - Exam Structure & Performance Optimization

Date: 2025-12-29
Migration ID: 0001_flawless_texas_twister
Author: Principal Database Architect

1. Summary

This release introduces support for hierarchical exam structures (Sectioning/Grouping) and optimizes database constraint naming for better compatibility with MySQL environments.

2. Changes

2.1 Table: `exams`

Action: ADD COLUMN
Field: structure (JSON)
Reason: To support nested exam layouts (e.g., "Part I: Listening", "Section A").
- Architecture Note: This JSON field is strictly for Presentation Layer ordering and grouping. The exam_questions table remains the Source of Truth for relational integrity and scoring logic.
- Schema Definition:
```
type ExamStructure = Array<
   | { type: 'group', title: string, children: ExamStructure }
   | { type: 'question', questionId: string, score: number }
>
```

2.2 Table: `questions_to_knowledge_points`

Action: RENAME FOREIGN KEY
Details:
- Old: questions_to_knowledge_points_question_id_questions_id_fk -> New: q_kp_qid_fk
- Old: questions_to_knowledge_points_knowledge_point_id_knowledge_points_id_fk -> New: q_kp_kpid_fk
Reason: Previous names exceeded MySQL's 64-character identifier limit, causing potential migration failures in production environments.

3. Migration Strategy

Up: Run standard Drizzle migration. The script includes ALTER TABLE ... DROP FOREIGN KEY followed by ADD CONSTRAINT.
Down: Revert structure column. Note that FK names can be kept short as they are implementation details.

4. Impact Analysis

Performance: Negligible. JSON parsing is done client-side or at application layer.
Data Integrity: High. Existing data is unaffected. New structure field defaults to NULL.

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