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igmarin/rails-agent-skills

Curated library of AI agent skills for Ruby on Rails development. Covers code review, architecture, security, testing (RSpec), engines, service objects, DDD patterns, and workflow automation.

98

1.38x
Quality

99%

Does it follow best practices?

Impact

98%

1.38x

Average score across 26 eval scenarios

SecuritybySnyk

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Files

PATTERNS.mdrails-migration-safety/

Advanced Migration Patterns

Reference for complex schema operations beyond add-column and add-index.

Type Changes

Never change a column type in a single migration on a busy table. Use the add-copy-migrate-drop approach:

# Step 1: add new column with new type
add_column :orders, :amount_cents, :bigint

# Step 2: backfill (separate deploy, in batches)
# Order.in_batches.update_all('amount_cents = CAST(amount * 100 AS BIGINT)')

# Step 3: migrate code references to new column, then drop old column
remove_column :orders, :amount

Multi-Step Unique Constraints

Adding a unique index on data that may have duplicates will fail at the database level:

  1. Query for duplicates: SELECT col, COUNT(*) FROM table GROUP BY col HAVING COUNT(*) > 1
  2. Resolve duplicates in application code or a data migration
  3. Add unique index concurrently after data is clean:
disable_ddl_transaction!
add_index :users, :email, unique: true, algorithm: :concurrent

Foreign Keys on Large Tables

Adding a foreign key validates all existing rows by default, which can lock the table:

# Step 1: add without validation (fast, no lock)
add_foreign_key :orders, :users, validate: false

# Step 2 (separate migration): validate after cleaning orphans
validate_foreign_key :orders, :users

Removing a Column Safely

Rails caches column information. Removing a column without first telling Active Record to ignore it causes ActiveModel::MissingAttributeError during the deploy window.

# Step 1: add to ignored_columns in the model (deploy this first)
class Order < ApplicationRecord
  self.ignored_columns += %w[legacy_field]
end

# Step 2 (next deploy): drop the column
remove_column :orders, :legacy_field

Multi-Database Migrations

When running migrations against a non-primary database, use connects_to in the migration class:

class AddIndexToAnalyticsEvents < ActiveRecord::Migration[7.2]
  def connection
    AnalyticsEvent.connection
  end

  def change
    disable_ddl_transaction!
    add_index :analytics_events, :occurred_at, algorithm: :concurrent
  end
end

rails-migration-safety

PATTERNS.md

SKILL.md

README.md

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