验证基于rails中下拉框的id

Question

我在输入过程中发生了验证，如下所示：

validates :solids, :numericality => { :greater_than_or_equal_to => 0 }, :if => lambda { 
  if self.lab_method_id
    lab_method = LabMethod.find(self.lab_method_id)
    lab_method.solids?
  end
}

我希望根据下拉框中选定的ID更改此条件。

我在我的模型中试过这个：

if self.lab_method_id == 1
validates :solids, :numericality => { :greater_than_or_equal_to => 0 }, :if => lambda { 
  if self.lab_method_id
    lab_method = LabMethod.find(self.lab_method_id)
    lab_method.solids?
  end
}
elsif
validates :solids, :numericality => { :greater_than_or_equal_to => 5 }, :if => lambda { 
  if self.lab_method_id
    lab_method = LabMethod.find(self.lab_method_id)
    lab_method.solids?
  end
}
end

但是这会在页面加载时返回错误：

未定义的方法`键？'为零：NilClass

我认为这与模型中的验证在页面加载时加载这一事实有关，而此时检查id的if语句将不起作用。虽然这个错误对我来说没有意义。

所以我想知道如何根据所选择的下拉框项目的ID选择特定的验证方式进行设置（我是否正确地获得了ID）？

额外奖励：有人可以解释与此特定错误的关系吗？

编辑 - 堆栈跟踪：

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Answer 1

NumericalityValidator（此帮助程序的基础验证程序）不适用于您想要的动态条件。使用自定义验证器：

validate :solids_validation

def solids_validation
  if self.lab_method_id
    lab_method = LabMethod.find(self.lab_method_id)
    if lab_method.solids?
      if (val = Kernel.Float(solids) rescue nil)
        min = (self.lab_method_id == 1 ? 0 : 5)
        errors.add(:solids, "must be greater than or equal to #{min}") if val < min
      else
        errors.add(:solids, :not_a_number)
      end
    end
  end
end