class CreateGuardianUsersTable < ActiveRecord::Migration
  def self.up
    create_table(:guardian_users) do |table|
      table.timestamps # I find them useful; YMMV
      table.integer :guardian_id
      table.integer :ward_id,:null => false,:references => [:students,:id]
      table.string :email
      table.string :heahead_password
    end
  end
 
  def self.down
    drop_table :guardian_users
  end
end

在你的模型中：

class GuardianUser < ActiveRecord::Base
  belongs_to :student
end
 
class Student < ActiveRecord::Base
  has_many guardian_users:,:foreign_key => 'ward_id',:class_name => 'GuardianUser',:dependent => :destroy
end