no-truncate

Reports TRUNCATE and queryRunner.clearTable(), which delete every row of a table.

Category	Default severity	Databases
data-loss	error	PostgreSQL, MySQL

What happens

TRUNCATE removes all rows at once. TypeORM's clearTable() runs TRUNCATE TABLE.

• On PostgreSQL it takes an ACCESS EXCLUSIVE lock, which blocks every read and write on the table until the migration's transaction ends. It is also not MVCC-safe: transactions that started before it see the table as empty.
• On MySQL it causes an implicit commit, so it cannot be rolled back.

Bad

import { MigrationInterface, QueryRunner } from 'typeorm'

export class ResetSessions1727200000000 implements MigrationInterface {
  public async up(queryRunner: QueryRunner): Promise<void> {
    await queryRunner.clearTable('sessions')
  }

  public async down(queryRunner: QueryRunner): Promise<void> {
    // ...
  }
}

Safe

Delete only the rows you mean to remove, in batches, with DELETE ... WHERE:

import { MigrationInterface, QueryRunner } from 'typeorm'

export class PruneSessions1727200000000 implements MigrationInterface {
  public async up(queryRunner: QueryRunner): Promise<void> {
    await queryRunner.query(`DELETE FROM "sessions" WHERE "expiresAt" < now() - interval '30 days'`)
  }

  public async down(queryRunner: QueryRunner): Promise<void> {
    // ...
  }
}

When to suppress

When the table only holds data that can be rebuilt, such as a cache, and briefly blocking it is acceptable.

// preflight safety-assured no-truncate -- sessions are recreated on next login

References

• PostgreSQL: TRUNCATE ("TRUNCATE acquires an ACCESS EXCLUSIVE lock on each table it operates on", "TRUNCATE is not MVCC-safe")
• MySQL: TRUNCATE TABLE ("Truncate operations cause an implicit commit, and so cannot be rolled back.")
• TypeORM: PostgresQueryRunner.clearTable