LowFile-scopeRuby Plug & play

Extract complex migration logic to separate methods

Keep migrations readable by extracting multi-step data fixes to helper methods within the migration.

Why this matters

Eases review and reduces errors in irreversible changes.

Side-by-side examples engineers can pattern-match during review.

Avoid

def change; User.find_each { |u| u.update!(x: compute(u)) }; end

Prefer

def up; backfill_x; end
private
def backfill_x; User.find_each { |u| u.update!(x: compute(u)) }; end

Bad

long loop inline

Good

helper method encapsulates loop

From the same buckets as this rule.

Critical
Block risky database migrations (locking ops, downtime risk)
Review SQL/database migrations for operations that can lock large tables or cause downtime. Examples: creating indexes without CONCURRENTLY (Postgres), ALTER COLUMN TYPE on big tables, adding NOT NULL without backfill, long-running updates without batching. Require an online migration strategy (CONCURRENTLY, backfill in batches, dual-write/expand-contract) and a rollback plan.
migrations-backward-compatdatabase-query-performance
Critical
Deletion requests: anonymize or hard-delete PII irreversibly
On LGPD deletion, remove or irreversibly anonymize PII and purge dependent caches. Keep minimal audit metadata (timestamp, request ID) not linkable back to the subject.
compliance-lgpdmigrations-backward-compat+1
High
Add foreign key constraints in migrations
Enforce referential integrity with add_foreign_key and matching indexes.
database-query-performancemigrations-backward-compat