Database with Sequelize ORM

Quick Guide: Sequelize is a promise-based ORM for PostgreSQL, MySQL, MariaDB, SQLite, and MS SQL Server. Use class-based models with Model.init() (v6) or decorators (v7) for type-safe definitions. Always use InferAttributes/InferCreationAttributes with declare for TypeScript models. Use include for eager loading to avoid N+1. Prefer managed transactions (auto-commit/rollback). Association alias (as) must match between definition and include. Paranoid mode requires timestamps: true. v7 is alpha --- most production code uses v6.

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CRITICAL: Before Using This Skill

All code must follow project conventions in CLAUDE.md (kebab-case, named exports, import ordering, import type, named constants)

(You MUST use declare on all model class properties to prevent TypeScript from emitting class fields that conflict with Sequelize's internal attribute storage)

(You MUST pass { transaction: t } to every query inside a transaction callback --- missing this causes operations to run outside the transaction and skip rollback)

(You MUST use include for eager loading related models --- fetching associations in loops creates N+1 query problems)

(You MUST match the as alias in include with the alias used in the association definition --- mismatches silently return null for the association)