Question

我有一个时间间隔为虚拟属性的模型：

attr_accessible :description, :time_end, :time_start, :duration
belongs_to :timesheet

def duration
  if attribute_present?("time_start") and attribute_present?("time_end")
    ChronicDuration.output(self.time_end - self.time_start) 
  else
    ChronicDuration.output(0)
  end
end

def duration=(d)
  self.time_end = self.time_start + d
end

但是，在创建新对象时，Rails会尝试在启动之前设置持续时间，从而导致错误。如何确保在开始后设置持续时间？

错误：

undefined method `+' for nil:NilClass

PARAMS：

{"utf8"=>"✓", "authenticity_token"=>"dg+CysIxZORyV3cwvD+LdWckFdHgecGDFDBNOip+iKo=", "entry"=>{"time_start"=>"now", "duration"=>"2h", "description"=>""}, "commit"=>"Create Entry"}

Answer 1

1。）命名属性end并不聪明，因为这是一个关键字，可能会造成一些麻烦。

2。）请发布您的参数哈希

Answer 2

一些事情

值得一读：and vs &&红宝石 - http://devblog.avdi.org/2010/08/02/using-and-and-or-in-ruby/

有些人会使用attribute_present吗？方法

# opposite of blank? - http://api.rubyonrails.org/classes/Object.html#method-i-present-3F
if time_start.present? && time_end.present?

# short hand syntax for present?
if time_start? && time_end?

我认为你的问题是在time_start之前设置的持续时间，假设time_start是datetime或time数据库类型在rails console中试试这个

entry = Entry.new
entry.time_start = "now" 
# => "now"
entry.time_start
# => nil

您将字符串传递给时间对象，rails / ruby只将值设置为nil。如果time_end和time_start是字符串，我仍然认为你的代码不会给你你想要的结果？

def duration=(d)
  self.time_end = self.time_start + d
end

# params: time_start = "now"
# params: duration = "2h"
# time_end would be: now2h

如果我在设置time_start之前运行持续时间=错误，那么使用before_save回调可以选择这样的替代方法

class Entry < ActiveRecord::Base
  before_save :set_time_end

  attr_accessor :duration
  attr_accessible :description, :time_end, :time_start, :duration

  belongs_to :timesheet

  def duration
    if time_start? && time_end?
      ChronicDuration.output(self.time_end - self.time_start) 
    else
      ChronicDuration.output(0)
    end
  end

  def set_time_end
    return nil if time_start.blank?
    self.time_end = self.time_start + self.duration
  end
end

使用真实属性设置虚拟属性

2 个答案: