SQLite Database & Serverless Storage

Database Architecture

Undoku’s Express.js testing and serverless backend uses SQLite (better-sqlite3) to provide persistence for Sudoku puzzles, solution matrices, candidate elimination metrics, and step-by-step deduction histories.

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Schema Model (puzzles table)

CREATE TABLE IF NOT EXISTS puzzles (
  id INTEGER PRIMARY KEY AUTOINCREMENT,
  solution TEXT NOT NULL,
  board_state TEXT NOT NULL,
  blanks_count INTEGER NOT NULL,
  difficulty_rating TEXT NOT NULL,
  granular_tier TEXT NOT NULL,
  total_score REAL NOT NULL,
  composite_score REAL NOT NULL,
  cross_horizontal_reasons INTEGER NOT NULL,
  cross_vertical_reasons INTEGER NOT NULL,
  box_3x3_reasons INTEGER NOT NULL,
  total_reasons INTEGER NOT NULL,
  technique_counts_json TEXT NOT NULL,
  deductions_json TEXT NOT NULL,
  advanced_metrics_json TEXT NOT NULL,
  created_at DATETIME DEFAULT CURRENT_TIMESTAMP
);

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Storage Layer (server/src/storage/db.js)

The DatabaseStorage class provides:

• savePuzzle(puzzleRecord): Saves evaluated puzzles and serializes step deductions to JSON.
• getPuzzle(id): Fetches full puzzle record and reconstructs deductions matrix.
• listPuzzles(filters): Supports pagination (limit, offset) and difficulty filtering (rating).
• In-Memory Testing Support: Accepts :memory: for ephemeral test runs.