Question

这是模型类 class Item :: Item＆lt;的ActiveRecord :: Base的 validates_presence_of：start_date，：end_date，：product_id validate：validate_start_and_end_date

         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 console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

Answer 1

它抱怨，因为在进入自定义验证时尚未设置start_date和end_date属性。当它试图将start_date与今天的日期进行比较时，它试图比较一个零值。

您可以将验证包装在条件块中：

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

Answer 2

请注意，您在控制台中创建的Item对象包含start_date的{{1}}，end_date等。

然后，验证方法中nil的比较导致异常。

Rails：错误＆＃34; NoMethodError：未定义的方法`＆lt;＆＃39;为nil：NilClass＆＃34;，错过了一些宝石？

2 个答案: