ruby-on-rails - 为什么我在 Rails 模型回调中收到此 "undefined method"错误，将方法作为符号传递？

Question

我有一个名为“Post”的类，它应该在更改或尚未转换时将其 Markdown 内容转换为 HTML。我正在尝试将 before_save 回调与 if: 一起使用参数，但我在传递给 if 的任何内容时都会收到此错误当我尝试运行测试时:

Testing started at 1:55 ... rake aborted!
undefined method 'markdown_changed_or_html_nil?' for #<Post:0x000000053603d0> C:/Users/user/Documents/GitHub/jw/app/models/post.rb:7:in <class:Post> C:/Users/user/Documents/GitHub/jw/app/models/post.rb:1:in <top (required)> C:/Users/user/Documents/GitHub/jw/test/test_helper.rb:12:in <class:TestCase> C:/Users/user/Documents/GitHub/jw/test/test_helper.rb:5:in <top (required)> C:/Users/user/Documents/GitHub/jw/test/models/post_test.rb:1:in <top (required)>
-e:1:in 'load'
-e:1:in '' Tasks: TOP => test:run => test:units (See full trace by running task with --trace) Run options: --seed 13458

# Running tests:

Finished tests in 0.002000s, 0.0000 tests/s, 0.0000 assertions/s.

0 tests, 0 assertions, 0 failures, 0 errors, 0 skips

Process finished with exit code 1

这是有问题的模型:

class Post < ActiveRecord::Base
  include ActiveModel::Dirty

  before_save :convert_markdown, if: :markdown_changed_or_html_nil?

  belongs_to :user
  validates :user, :title, :content_markdown, { presence: true, on: create }
  validates_associated :user

  protected
    def convert_markdown
      markdown = Redcarpet::Markdown.new(Redcarpet::Render::HTML, space_after_headers: true, underline: true)
      self.content_html = markdown.render(content_markdown)
    end

    def markdown_changed_or_html_nil?
      content_markdown.changed? || content_markdown.nil?
    end
end

我正在使用 Ruby 2.0.0 和 Rails 4.0.2。

我很可能犯了一个非常非常基本的错误 - 我仍在学习 Rails。

---

编辑:这是post_test.rb

require 'test_helper'

class PostTest < ActiveSupport::TestCase
  test 'saving an empty object fails' do
    new_post = Post.new

    assert_not new_post.save
  end

  test 'validates that given user id corresponds to user' do
    # This will create a user with a given id so we can use the next one up
    test_user = User.create({ name: 'Johnny Test', email: 'johnny.test@example.com',
                            password: 'password', password_confirmation: 'password' })

    # Use next id up - there's no reason it should be taken at this point
    given_user_id = test_user.id + 1

    post_with_invalid_user = Post.new({ title: 'Look at my glorious title', content_markdown: 'Sick content',
                                      user_id: given_user_id })

    assert_not post_with_invalid_user.save
  end

  test 'converts markdown into html' do
    # This is a really really basic test just to make sure a conversion happens
    new_post = Post.new({ title: 'Check out this markdown, baby', content_markdown: 'I got some *sick* markdown',
                        user_id: users(:paul).id })

    assert_equal '<p>I got some <em>sick</em> markdown</p>', new_post.content_html
  end
end

Answer 1

这可能不是您的主要问题(因为您的错误消息似乎与此无关)，但您没有正确使用 changed?。 changed? 需要在您的模型对象上调用，可以选择使用您的属性名称作为前缀。所以你的条件方法应该是这样的:

def markdown_changed_or_html_nil?
  # based on your method name, shouldn't this be:
  # content_markdown_changed? || content_html.nil?
  content_markdown_changed? || content_markdown.nil?
end

在 http://api.rubyonrails.org/classes/ActiveModel/Dirty.html 找到更多关于 Dirty 方法的信息.

还有

我很确定 Rails 4 没有将 Dirty 移出 ActiveRecord::Base，因此您不需要手动 include ActiveModel: :Dirty 在你的模型中。

还有

这一行:

validates :user, :title, :content_markdown, { presence: true, on: create }

应该是:

validates :user, :title, :content_markdown, { presence: true, on: :create }