ruby on rails-validate_presence_of在使用增量计数器时未按预期工作

Question

考虑以下代码：

campaign_spec.rb:

describe Campaign do
  before :each do
    @campaign = Campaign.new
  end
  it { should validate_presence_of :position }
end

活动.rb:

class Campaign < ActiveRecord::Base
  attr_accessible :position
  validates :position, presence: true
  default_scope order(:position)
  before_validation :next_position
  # sets the position to the next id (1 if none exist) before validation
  def next_position
    if self.position.blank?
      self.position = Campaign.select("coalesce(max(position),0) + 1 as position").reorder(nil).first.position
    end
  end
end

规格输出：

Failures:
  1) Campaign should require position to be set
     Failure/Error: it { should validate_presence_of :position }
       Expected errors to include "can't be blank" when position is set to nil, got errors: ["name can't be blank (nil)"]
     # ./spec/models/campaign_spec.rb:9:in `block (2 levels) in <top (required)>'

根据我的模型所说，我应该能够在不给它定位的情况下创建Campaign。如果在验证前不存在，则设置位置。那么，为什么我的规范没有通过呢？我在想，也许它没有调用我的before_validation方法？

Answer 1

should validate_presence_of将属性的值设置为nil，然后运行验证。由于它为零，nil.blank?返回true，因此执行回调，将其设置回某个值，因此发现验证不起作用。

事实是，如果您确信该字段从不为空，则不需要验证该字段。相反，编写测试以检查当设置为nil时是否确实自动填充了它。

it 'populates position if blank before validations' do
  subject.position = nil
  subject.valid?
  subject.position.should_not be_nil
end