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