migration_helper.rb

module MigrationHelper
  #options are:
  # :pk_table_name
  # :pk_column_name
  # :cascade_delete
  # :cascade_update
  def add_fk(fk_table_name, fk_column_name, options)
    fk_table_name = fk_table_name.to_s
    fk_column_name = fk_column_name.to_s
    pk_table_name = options[:pk_table_name] || fk_column_name[0, fk_column_name.index("_id") || fk_column_name.length]
    pk_column_name = options[:pk_column_name] || "id"
    cascade_delete = options[:cascade_delete] ? "on delete cascade" : ""
    cascade_update = options[:cascade_update] ? "on update cascade" : ""
    execute "alter table #{fk_table_name} add constraint fk_#{fk_table_name}_#{fk_column_name} foreign key (#{fk_column_name}) references #{pk_table_name.to_s} (#{pk_column_name.to_s}) #{cascade_delete} #{cascade_update}"
    execute "create index idx_#{fk_table_name}_#{fk_column_name} on #{fk_table_name} (#{fk_column_name})"
  end

  def drop_fk(fk_table_name, fk_column_name)
    execute "drop index #{fk_table_name}.idx_#{fk_table_name}_#{fk_column_name}"
    execute "alter table #{fk_table_name.to_s} drop constraint fk_#{fk_table_name.to_s}_#{fk_column_name.to_s}"
  end
end

class ActiveRecord::Migration
  extend MigrationHelper
end