Get list of foreign keys without indexes: source http://tomafro.net/2009/09/quickly-list-missing-foreign-key-indexes

gistfile1.rb

c = ActiveRecord::Base.connection
c.tables.collect do |t|  
  columns = c.columns(t).collect(&:name).select {|x| x.ends_with?("_id" || x.ends_with("_type"))}
  indexed_columns = c.indexes(t).collect(&:columns).flatten.uniq
  unindexed = columns - indexed_columns
  unless unindexed.empty?
    unindexed.each do |ui|
      puts "add_index :#{t}, :#{ui}"
    end
  end
end