mmk down

Rolls migrations back by running their down(). By default it undoes the last batch.

npx mmk down [file] [options]

Examples

npx mmk down                     # the last batch
npx mmk down <file>              # one file
npx mmk down --batch 3           # everything in batch 3
npx mmk down --steps 2           # the last two files, whatever their batch

What it does

mmk takes the lock, works out which files to undo, and runs their down() newest first.

$ npx mmk down
Loaded config from mmk.config.js
↩ Reverted 20261015110000-rename-user-name.js   [25ms]
↩ Reverted 20261014103000-add-orders-customer-index.js   [4ms]

Records aren't deleted. Each one gets status: 'reverted' and a revertedAt date, and the file shows as pending again.

Not sure what it'll undo? Put dry-run in front: npx mmk dry-run down --steps 2.

Options

Option	What it does
[file]	Undo only this file.
--batch <n>	Undo every file in batch n.
--steps <n>	Undo the last n files, newest first, ignoring batches.
--force	Undo even if a file changed since it ran. Asks you to confirm.
--yes	Answer yes to the --force question. Needed with --json.
--no-lock	Don't take the lock. Only for local development.
--json	Print the results as JSON on stdout.

--steps can't be combined with a file name or with --batch. mmk tells you before it connects:

✖ INVALID_ARGUMENT: Cannot combine --batch with --steps — they select different things
  Received: --batch 2 and --steps 1
  --batch 2 rolls back everything applied in batch 2
  --steps 1 rolls back the last 1 migration(s), ignoring batches

A batch that doesn't exist is an error too, and lists the ones that do:

✖ INVALID_ARGUMENT: No applied migrations found in batch 99
  Batches that still have applied migrations: 2, 3
  Run `mmk status` to see the batch number of each migration

Edited files are refused

Before it undoes anything, mmk down checks every file against the checksum saved when it ran. If any of them changed, it stops before undoing anything at all:

✖ CHECKSUM_MISMATCH: Refusing to roll back a file that changed since being applied: 20261012091500-backfill-order-status.js
  Rolling back would run the CURRENT down(), which may not undo what the applied up() did
  Restore the file to the version that was applied, then roll back
  Or roll back with the current code anyway: mmk down 20261012091500-backfill-order-status.js --force

This check is always on, whatever strict says. Running edited rollback code against production is the riskiest thing a migration tool can do, so mmk wants you to say so explicitly with --force. mmk redo skips this check, because redoing a file you just edited is what it's for.

Imported migrations

Migrations brought over from migrate-mongo with mmk import can't be rolled back by mmk. mmk down checks for them first and refuses with MIGRATION_IRREVERSIBLE before touching anything, so you never end up with half a batch undone.

Exit codes

Code	Meaning
0	The files were rolled back, or there was nothing to roll back.
1	A down() failed, the file wasn't applied, a file changed (without --force), or the command was wrong.