fix(db-postgres): keep generated down migrations idempotent

packages/db-postgres/src/index.ts

@@ -53,6 +53,7 @@ import {
   execute,
   init,
   insert,
+  makePostgresDropsIdempotent,
   requireDrizzleKit,
 } from '@payloadcms/drizzle/postgres'
 import { pgEnum, pgSchema, pgTable } from 'drizzle-orm/pg-core'
@@ -104,7 +105,7 @@ export function postgresAdapter(args: Args): DatabaseAdapterObj<PostgresAdapter>
       sqlExecute: string
       statements: string[]
     }): string => {
-      return `${sqlExecute}\n ${statements.join('\n')}\`)`
+      return `${sqlExecute}\n ${makePostgresDropsIdempotent(statements).join('\n')}\`)`
     }
 
     const executeMethod = 'execute'

packages/db-vercel-postgres/src/index.ts

@@ -54,6 +54,7 @@ import {
   execute,
   init,
   insert,
+  makePostgresDropsIdempotent,
   requireDrizzleKit,
 } from '@payloadcms/drizzle/postgres'
 import { pgEnum, pgSchema, pgTable } from 'drizzle-orm/pg-core'
@@ -100,7 +101,7 @@ export function vercelPostgresAdapter(args: Args = {}): DatabaseAdapterObj<Verce
     }: {
       sqlExecute: string
       statements: string[]
-    }) => `${sqlExecute}\n ${statements.join('\n')}\`)`
+    }) => `${sqlExecute}\n ${makePostgresDropsIdempotent(statements).join('\n')}\`)`
 
     const adapter = createDatabaseAdapter<VercelPostgresAdapter>({
       name: 'postgres',

packages/drizzle/src/exports/postgres.ts

@@ -9,6 +9,7 @@ export { dropDatabase } from '../postgres/dropDatabase.js'
 export { execute } from '../postgres/execute.js'
 export { init } from '../postgres/init.js'
 export { insert } from '../postgres/insert.js'
+export { makePostgresDropsIdempotent } from '../utilities/makePostgresDropsIdempotent.js'
 export { migratePostgresLocalizeStatus } from '../postgres/predefinedMigrations/localize-status/index.js'
 export { migratePostgresV2toV3 } from '../postgres/predefinedMigrations/v2-v3/index.js'
 export { requireDrizzleKit } from '../postgres/requireDrizzleKit.js'

packages/drizzle/src/utilities/makePostgresDropsIdempotent.spec.ts

@@ -0,0 +1,43 @@
+import { describe, expect, it } from 'vitest'
+
+import { makePostgresDropsIdempotent } from './makePostgresDropsIdempotent.js'
+
+describe('makePostgresDropsIdempotent', () => {
+  it('rewrites DROP CONSTRAINT to DROP CONSTRAINT IF EXISTS', () => {
+    const input = ['ALTER TABLE "posts_rels" DROP CONSTRAINT "posts_rels_posts_fk";']
+    expect(makePostgresDropsIdempotent(input)).toEqual([
+      'ALTER TABLE "posts_rels" DROP CONSTRAINT IF EXISTS "posts_rels_posts_fk";',
+    ])
+  })
+
+  it('rewrites DROP INDEX to DROP INDEX IF EXISTS', () => {
+    const input = ['DROP INDEX "posts_title_idx";']
+    expect(makePostgresDropsIdempotent(input)).toEqual(['DROP INDEX IF EXISTS "posts_title_idx";'])
+  })
+
+  it('does not double-rewrite statements that already use IF EXISTS', () => {
+    const input = [
+      'ALTER TABLE "posts_rels" DROP CONSTRAINT IF EXISTS "posts_rels_posts_fk";',
+      'DROP INDEX IF EXISTS "posts_title_idx";',
+    ]
+    expect(makePostgresDropsIdempotent(input)).toEqual(input)
+  })
+
+  it('leaves CREATE INDEX and other DDL untouched', () => {
+    const input = [
+      'CREATE INDEX IF NOT EXISTS "posts_title_idx" ON "posts" USING btree ("title");',
+      'DROP TABLE "posts_rels" CASCADE;',
+      'ALTER TABLE "posts" ADD COLUMN "slug" varchar;',
+    ]
+    expect(makePostgresDropsIdempotent(input)).toEqual(input)
+  })
+
+  it('handles multiple drops in a single statement', () => {
+    const input = [
+      'ALTER TABLE "posts_rels" DROP CONSTRAINT "posts_rels_posts_fk", DROP CONSTRAINT "posts_rels_categories_fk";',
+    ]
+    expect(makePostgresDropsIdempotent(input)).toEqual([
+      'ALTER TABLE "posts_rels" DROP CONSTRAINT IF EXISTS "posts_rels_posts_fk", DROP CONSTRAINT IF EXISTS "posts_rels_categories_fk";',
+    ])
+  })
+})

packages/drizzle/src/utilities/makePostgresDropsIdempotent.ts

@@ -0,0 +1,21 @@
+/**
+ * Rewrites `DROP CONSTRAINT` and `DROP INDEX` statements emitted by drizzle-kit so they
+ * include `IF EXISTS`. Postgres resolves dependent foreign keys when a referenced table
+ * is dropped with `CASCADE`, which causes follow-up explicit drops in the same migration
+ * to fail. Making these drops idempotent keeps the generated up/down migrations runnable
+ * end-to-end.
+ *
+ * Only rewrites statements that don't already contain `IF EXISTS` to stay safe against
+ * future drizzle-kit output changes.
+ */
+export const makePostgresDropsIdempotent = (statements: string[]): string[] =>
+  statements.map((statement) => {
+    let next = statement.replace(
+      /\bDROP CONSTRAINT\b(?! IF EXISTS\b)/gi,
+      'DROP CONSTRAINT IF EXISTS',
+    )
+
+    next = next.replace(/\bDROP INDEX\b(?! IF EXISTS\b)/gi, 'DROP INDEX IF EXISTS')
+
+    return next
+  })