Ruby On Rails-模型的属性和访问器范围

Question

I need some help with the scope of instance variables and accessors in a Ruby on Rails model.

Here is a simplification of my model (a blog article). I've removed the irrelevant parts. Of course it has a set of validations, associations and custom methods.

# Table name: articles
#
#  author_url   :string(255)
#  display_date :datetime

class Article < ActiveRecord::Base
  attr_accessible :author_url, :display_date

  # callbacks
  before_create :prepare_properties

  # validations
  VALID_URL_REGEX = /\Ahttps?:\/\/.+/i
  validates :author_url, format: { with: VALID_URL_REGEX,
                                message: " can only use http:// or https:// schemes",
                                     if: Proc.new { author_url.include?("://") } }

  private

    def prepare_properties
      display_date ||= Time.now
      author_url.prepend("http://") unless author_url =~ /\Ahttps?:\/\//i
    end
end

Now:

• author_url is first checked with a validator that ensures that it begins with either http:// , https:// or nothing.
• on object creation, this should happen:
  • if author_url doesn't already have a (valid) url scheme, http:// is prepended by default.
  • If the author has not indicated a display_date, Time.now is used.

The problem is that the author_url accessor works as expected, but the display_date one is treated as a local variable scoped within the method. The same happens if I use the callback with a block rather than a separate method.

The only way to make it work, is to use self.display_date .

Still, I'm wondering why this happens for just one property and not the other.

Answer 1

You need to use self. to call setters for the current object.

self.display_date ||= Time.now

Without self. , it becomes ambiguous as to whether you want to create a local variable or call the setter, and Ruby chooses creating local variable by default.

Still, I'm wondering why this happens for just one property and not the other.

Because you're not setting author_url to anything; you're just calling a method on it, which is fetched using the getter. The author_url= setter is never called.