Database Skill

Database Workflow

Apply this skill any time work involves database schema, queries, repositories, or migrations.

Environment Assumptions

1. Assume MySQL 8+ in all target environments.
2. Assume Aurora MySQL in staging/production.
3. Assume Docker MySQL locally.

Schema Change Rules

1. Implement schema changes through TypeORM entities in src/entities (sometimes documented as src/entitites).
2. Keep entity file naming pattern:
   • File name prefixed with I, example: IMyThing.ts
   • Class name without I and suffixed with Entity, example: MyThingEntity
3. Treat edits to existing entities as high risk and check for possible data loss before changing types or columns.
4. Never use foreign keys.
5. Prefer UUID primary keys unless sequential IDs are strictly required.
6. Prefer bigint Unix epoch milliseconds for time fields over SQL datetime/date.
7. For every new @Entity(TABLE_NAME), add/use a table constant in src/constants/db-tables.ts (example: MY_THINGS_TABLE).
8. Keep entity class/file names singular; keep table names plural (example table: my_things).

Query and Repository Rules

1. Isolate DB access inside repository-style classes (usually *Repository, sometimes *Db).
2. Use caller-level transactions only when work must span multiple repositories:

await sqlExecutor.executeNativeQueriesInTransaction(async (connection) => {
  // do all the transactional stuff here by passing the connection with context
});

3. Make ctx: RequestContext the last argument of repository functions.
4. Time every repository function with this pattern:

try {
  ctx.timer?.start(`${this.constructor.name}->nameOfTheCalledRepositoryFunction`);
  // do whatever you need to do here
} finally {
  ctx.timer?.stop(`${this.constructor.name}->nameOfTheCalledRepositoryFunction`);
}

5. Use ctx.connection when present, so operations participate in caller-provided transactions.
6. Never use generated Api* classes in repositories.
7. Allow callers (services/routes/etc.) to use entity classes and repository-defined types.
8. Use constants from src/constants/db-tables.ts instead of hardcoded table names whenever possible.
9. Prefer typed queries via execute<T>() and oneOrNull<T>().

Data Migration Rules

1. Use db-migrate only for data migration.
2. Never use db-migrate for schema changes.
3. Create migrations with:

npm run migrate:new migration-name

4. Edit files created under migrations/.
5. Delete the down migration path; do not implement revert logic.

Practical Checklist

• Kept schema changes in entity classes (not SQL migrations).
• Preserved entity naming convention (I*.ts file, *Entity class).
• Checked entity edits for data-loss risk.
• Avoided foreign keys.
• Used UUID PK unless sequential ID was required.
• Used epoch-millis bigint for time where applicable.
• Added/used table name constants in src/constants/db-tables.ts.
• Kept table names plural and entity names singular.
• Kept DB logic in repository/*Db classes.
• Used transaction wrapper only when spanning repositories.
• Passed ctx: RequestContext as last parameter.
• Added timer start/stop in repository methods.
• Used ctx.connection when available.
• Avoided generated Api* models in repositories.
• Used typed query methods and table constants in SQL.
• Used db-migrate only for data migration and removed down path.

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