require-down

Reports a migration whose down() is empty or missing, so reverting it changes nothing but still marks it as not applied.

Category	Default severity	Databases
correctness	warn	PostgreSQL, MySQL

What happens

typeorm migration:revert runs the last migration's down(), then deletes the migration from the migrations table. With an empty down(), nothing in the database changes, but TypeORM now records the migration as not applied. The next migration:run runs its up() again on a schema that already has its changes, and usually fails, for example with column "bio" already exists.

A down() that only has comments counts as empty. A down() that throws does not: throwing is the right way to say a migration cannot be reverted.

Bad

import { MigrationInterface, QueryRunner } from 'typeorm'

export class AddUserBio1727200000000 implements MigrationInterface {
  public async up(queryRunner: QueryRunner): Promise<void> {
    await queryRunner.query(`ALTER TABLE "users" ADD "bio" text`)
  }

  public async down(queryRunner: QueryRunner): Promise<void> {
    // nothing to undo
  }
}

Safe

import { MigrationInterface, QueryRunner } from 'typeorm'

export class AddUserBio1727200000000 implements MigrationInterface {
  public async up(queryRunner: QueryRunner): Promise<void> {
    await queryRunner.query(`ALTER TABLE "users" ADD "bio" text`)
  }

  public async down(queryRunner: QueryRunner): Promise<void> {
    await queryRunner.query(`ALTER TABLE "users" DROP COLUMN "bio"`)
  }
}

When the change cannot be undone, for example because it deletes data, say so:

public async down(): Promise<void> {
  throw new Error('This migration deletes the legacy table and cannot be reverted.')
}

When to suppress

Rarely: a down() that throws is clearer than a suppression. Suppress when reverting is never used in your deploy process and the team agrees on that.

// preflight safety-assured require-down -- we only roll forward; reverts are new migrations

References

• TypeORM 1.x: MigrationExecutor.undoLastMigration (runs down(), then deletes the migration record)
• TypeORM 0.3.x: MigrationExecutor.undoLastMigration