Grunt‑migrate rollback leaves data changes intact when undo script missing

Answer

Grunt‑migrate does not warn or abort a rollback when a migration contains data changes but lacks a matching down function. The runner simply executes whatever down exports (or nothing if it is missing) and marks the migration as rolled back, so any INSERT/UPDATE/DELETE performed in up remains in the database.

Explanation vs. confirmed facts

• Confirmed: The underlying node-migrate library that Grunt‑migrate wraps invokes only the down export during grunt migrate:down. If down is absent or empty, no automatic data reversal occurs.
• Likely explanation: Because the toolchain has no static analysis for data‑mutating calls, it cannot detect that a migration altered data without a corresponding undo. Some versions of node-migrate treat a missing down as a no‑op during down runs, which produces the silent inconsistency described.

Steps needed for this case

1. Ensure every migration that touches data includes a down that exactly reverses the change (e.g., reverse UPDATE, delete inserted rows by a deterministic WHERE clause, or restore from a backup table).
2. If a transformation is truly irreversible, document it as an exception and consider making it a separate, manual data‑migration step that is not run via grunt migrate.
3. Wrap migrations in a transaction when your database supports transactional DDL (e.g., PostgreSQL). This guarantees that a failing down rolls back cleanly, but it does not compensate for a missing down.
4. Add a custom pre‑rollback check (Grunt task or CI lint) that scans migration files and fails when up contains data‑mutation statements while down is missing or trivially empty. Example lint:

// grunt‑task: check‑migration‑downs
module.exports = function(grunt) {
  grunt.registerTask('check-migration-downs', 'Fail if up mutates data without down', function() {
    const fs = require('fs');
    const path = require('path');
    const migrationsDir = './migrations';
    const dataMutations = /\b(INSERT\s+INTO|UPDATE\s+|DELETE\s+FROM)\b/i;
    const files = fs.readdirSync(migrationsDir);
    let bad = [];
    for (const file of files) {
      const content = fs.readFileSync(path.join(migrationsDir, file), 'utf8');
      const hasUp = /exports\.up\s*=/.test(content);
      const hasDown = /exports\.down\s*=/.test(content);
      const mutates = dataMutations.test(content);
      if (hasUp && mutates && (!hasDown || /exports\.down\s*=\s*function\s*\(\s*\)\s*\{\s*\}/.test(content))) {
        bad.push(file);
      }
    }
    if (bad.length) {
      grunt.fail.fatal('Migrations missing down for data changes: ' + bad.join(', '));
    }
  });
};

Missing diagnostic detail

To confirm whether your specific installation treats a missing down as a silent no‑op or throws an error, we need to know the exact version of grunt‑migrate (or the underlying node-migrate package) you are using. Please provide the version from package.json so we can advise if any version‑specific behavior changes the recommendation.