orm-preflight

Appearance

possible-rename-data-loss ​

Warns when a migration drops one column and adds a different one on the same table without copying data, which is what a renamed entity property produces.

CategoryDefault severityDatabases
data-losswarnPostgreSQL, MySQL

What happens ​

When you rename an entity property and its column name follows, migration:generate cannot tell a rename from a removal plus an addition. Depending on the change it writes RENAME COLUMN, or it drops the old column and adds the new one. In the second case the old values are deleted and the new column starts empty.

This rule fires when a migration drops exactly one column and adds exactly one other column on the same table, and no INSERT or UPDATE on that table between the add and the drop copies the data. It is a warning because the two columns may really be unrelated. The dropped column is still reported by no-drop-column.

Bad ​

ts
import { MigrationInterface, QueryRunner } from 'typeorm'

export class RenameUserFullName1727200000000 implements MigrationInterface {
  public async up(queryRunner: QueryRunner): Promise<void> {
    await queryRunner.query(`ALTER TABLE "users" DROP COLUMN "fullName"`)
    await queryRunner.query(`ALTER TABLE "users" ADD "displayName" character varying`)
  }

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

Safe ​

Keep the data with expand and contract. First release: add the new column and backfill it.

ts
import { MigrationInterface, QueryRunner } from 'typeorm'

export class AddUserDisplayName1727200000000 implements MigrationInterface {
  public async up(queryRunner: QueryRunner): Promise<void> {
    await queryRunner.query(`ALTER TABLE "users" ADD "displayName" character varying`)
    await queryRunner.query(`UPDATE "users" SET "displayName" = "fullName"`)
  }

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

Switch the code to the new column, then drop fullName in a later release. If you only want a new property name, keep the column name instead: @Column({ name: 'fullName' }) displayName: string needs no migration at all.

When to suppress ​

When the two columns are unrelated, for example one feature is removed and another is added in the same migration.

ts
// preflight safety-assured possible-rename-data-loss -- fullName is unused since 2.4; displayName is new

References ​