# 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**:
        ```typescript
        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`.