Shoulda和before_回调

Question

我有一个简单的模型：

class Category < ActiveRecord::Base
  belongs_to :board
  validates :name, presence: true, uniqueness: {scope: :board_id}
  validates :board, presence: true
  validates :display_order, presence: true, uniqueness: {scope: :board_id}

  before_save :set_display_order

  private

  def set_display_order
    last = self.board.categories.order("display_order DESC").last
    self.display_order = last.display_order + 100 if last
  end
end

当我添加这个before_save回调时，这些测试开始失败：

  it { should validate_uniqueness_of(:display_order).scoped_to(:board_id) }
  it { should validate_uniqueness_of(:name).scoped_to(:board_id) }

With error (如果是私有方法last = ...中的行)：

 NoMethodError:
   undefined method `categories' for nil:NilClass

其他的测试应该可以正常工作：

  it { should validate_presence_of(:name) }
  it { should validate_presence_of(:board) }
  it { should belong_to :board }

你知道这里有什么问题吗？我尝试将before_save更改为before_validation，但仍然是一样的。

Answer 1

因为应该在数据库中创建记录。Gem创建记录跳过验证

http://rubydoc.info/github/thoughtbot/shoulda-matchers/master/Shoulda/Matchers/ActiveModel#validate_uniqueness_of-instance_method Ensures that the model is invalid if the given attribute is not unique. It uses the first existing record or creates a new one if no record exists in the database. It simply uses ':validate => false' to get around validations, so it will probably fail if there are 'NOT NULL' constraints. In that case, you must create a record before calling 'validate_uniqueness_of'.

在您的例子中，created category是空的，它表示category.board # => nil，您从nil调用categories方法。

您应该自己创建一条记录，用于唯一性测试。

Answer 2

绕过shoulda_matchers和AR回调的这种限制的一种方法是重新定义匹配器应该使用的测试主题。

示例：

# category_spec.rb

# assuming you're using factorygirl and have this setup correctly
let(:board) { FactoryGirl.create(:board, :with_many_categories) }
subject { FactoryGirl.build(:category, board: board) }

# your shoulda matcher validations here