Migrations流水帐

module MigrationHelpers
  # Add foreign key for migrations
  # Usage:
  # * /db/migrate/xxxx_create_users.rb
  # class CreateUsers < ActiveRecord::Migration
  #   extend MigrateionHelpers
  #   def self.up
  #     ...
  #     add_foreign_key :users, :group_id :groups
  #   end
  #   def down.up
  #     ...
  #     remove_foreign_key  :users, :group_id
  #   end
  # end
  #
  
  def add_foreign_key(from_table, from_column, to_table, to_column = 'id')
    constraint_name = "fk_#{from_table}_#{from_column}"
    execute "ALTER TABLE #{from_table} ADD CONSTRAINT #{constraint_name} FOREIGN KEY (#{from_column}) REFERENCES #{to_table} (#{to_column})"
  end
  
  def remove_foreign_key(from_table, from_column)
    constraint_name = "fk_#{from_table}_#{from_column}"
    execute "ALTER TABLE #{from_table} DROP CONSTRAINT #{constraint_name}"
  end
end