indexes.rb

namespace :db do
  namespace :indexes do
    desc "Prints a list of unindexed foreign keys so you can index them"
    task :missing => :environment do
      indexes = {}
      conn = ActiveRecord::Base.connection
      conn.tables.each do |table|
        indexed_columns = conn.indexes(table).map { |i| i.columns }.flatten
        conn.columns(table).each do |column|
          if column.name.match(/_id/) && !indexed_columns.include?(column.name)
            indexes[table] ||= []
            indexes[table] << column.name
          end
        end
      end
      puts "Foreign Keys:"
      indexes.each do |table, columns|
        puts columns.map { |c| "\s\sadd_index '#{table}', '#{c}'\n"}
      end
    end
  end
end