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.

<critical_requirements>

CRITICAL: Before Using This Skill

(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)

</critical_requirements>