Rails：错误“NoMethodError: undefined method `<' for nil:NilClass”，缺少一些宝石？答案

【问题标题】：Rails: Error "NoMethodError: undefined method `<' for nil:NilClass", missing some gem?Rails：错误“NoMethodError: undefined method `<' for nil:NilClass”，缺少一些宝石？
【发布时间】：2011-03-21 22:45:03
【问题描述】：

这里是模型类类 Item::Item

         def validate_start_and_end_date
             errors.add(:start_date, "should not be in past") if start_date < Date.today
             errors.add(:end_date, "should not be in past") if end_date < Date.today
             errors.add(:base, "start date should not be after end date") if end_date <  start_date
         end

         belongs_to :product, {:class_name => 'Item::Product'}

   end

这是rails控制台的日志

    ruby-1.8.7-p334 :020 > item = Item::Item.new 
    => #<Item::Item id: nil, start_date: nil, end_date: nil, product_id: nil> 
    ruby-1.8.7-p334 :021 > item.valid?
    NoMethodError: undefined method `<' for nil:NilClass
    from /home/maddy/.rvm/gems/ruby-1.8.7-p334/gems/activesupport-3.0.3/lib/active_support/whiny_nil.rb:48:in `method_missing'
    from /media/Development/codie/orgstud-security/app/models/lecture/lecture.rb:13:in `validate_start_and_end_date'
    from /home/maddy/.rvm/gems/ruby-1.8.7-p334/gems/activesupport-3.0.3/lib/active_support/callbacks.rb:419:in `_run_validate_callbacks'
    from /home/maddy/.rvm/gems/ruby-1.8.7-p334/gems/activemodel-3.0.3/lib/active_model/validations.rb:212:in `run_validations!'
    from /home/maddy/.rvm/gems/ruby-1.8.7-p334/gems/activemodel-3.0.3/lib/active_model/validations/callbacks.rb:67:in `run_validations!'
    from /home/sgarg/.rvm/gems/ruby-1.8.7-p334/gems/activesupport-3.0.3/lib/active_support/callbacks.rb:413:in `_run_validation_callbacks'
    from /home/maddy/.rvm/gems/ruby-1.8.7-p334/gems/activemodel-3.0.3/lib/active_model/validations/callbacks.rb:67:in `run_validations!'
    from /home/maddy/.rvm/gems/ruby-1.8.7-p334/gems/activemodel-3.0.3/lib/active_model/validations.rb:179:in `valid?'
    from /home/maddy/.rvm/gems/ruby-1.8.7-p334/gems/activerecord-3.0.3/lib/active_record/validations.rb:55:in `valid?'
from (irb):21

【问题讨论】：

标签： ruby-on-rails model gem ruby-on-rails-plugins nomethoderror

【解决方案1】：

它在抱怨，因为在进行自定义验证时尚未设置 start_date 和 end_date 属性。当它尝试将 start_date 与今天的日期进行比较时，它会尝试比较一个 nil 值。

您可以将验证包装在条件块中：

if !start_date.nil? && !end_date.nil?
  ...
end

【讨论】：

unless start_date.nil? && end_date.nil?

【解决方案2】：

请注意，您在控制台中创建的Item 对象具有start_date、end_date 等nil。

那么，在您的验证方法中比较 nil < Date.today 会导致异常。

【讨论】：

我刚刚看到第一个代码块描述了Lecture::Lecture 模型。您可以发布Item::Item 模型吗？（可能是同样的问题，但我不能确定。）