Rails宝典之第十四式: Model上的calculations

没什么新意: 

 >> Task.sum(:priority)
 => 15
 >> Task.sum(:priority, :conditions => 'complete=0')
 => 13
 >> Task.maximum(:priority)
 => 4
 >> Task.minimum(:priority)
 => 1
 >> Task.average(:priority)
 => 2.5
 >> p = Project.find(:first)
 => #<Project:0x32dce38 @attrbutes={"name" => "Programming", "id" => "1"}>
 >> p.tasks.sum(:priority)
 => 9
 >> p.tasks.sum(:priority, :conditions => 'complete=0')
 => 7