Rails中未定义的方法sort_by

Question

I am facing issues while using sort or sort_by in my presenter and controller. It says undefined method 'sort_by' .

Does it belong to any particular class? I have looked it up online but I am not able to find anything concrete.

Can any one shed light on this?

Here is my presenter code-

def sortDocument()
    @list.sort do |a, b|
      (b.published_date <=> a.published_date) ||
      a.display_name <=> b.display_name
      @list
end

and alternatively

def sortDocument()
  @list.sort_by!{ |m| m.published_date }
end

EDIT:

Error message:

undefined method `sort_by!' for #<DocumentsBureauServices::DocumentList:0x007ff8250f8a28>

presenter-

class DocumentPresenter

  def initialize(list)
    @list = list
    @list = sort_document()
  end
 def sortDocument()
    @list.sort do |a, b|
      (b.published_date <=> a.published_date) ||
      a.display_name <=> b.display_name
      @list
 end
end

and alternatively

 def sortDocument()
      @list.sort_by!{ |m| m.published_date }
    end

Answer 1

Sorts enum using a set of keys generated by mapping the values in enum through the given block...to use sort_by ...

%w{ apple pear fig }.sort_by {|word| word.length}
              #=> ["fig", "pear", "apple"]

Answer 2

It looks like the DocumentsBureauServices::DocumentList doesn't include the enumerable module and doesn't have access to the sort_by method.

If indeed DocumentList is a decorator around an enumerable object then you could use a delegator. ActiveSupport has a method dedicated to delegating: http://apidock.com/rails/Module/delegate

In your case, you could use it like this:

class DocumentsBureauServices::DocumentList

  delegate :sort_by!, to: :my_enumerable

  def initialize(enumerable)
    @my_enumerable = enumerable
  end

end

And then you could call sort_by! on your list object like this:

@list = DocumentsBureauServices::DocumentList.new(Document.all)
@list.sort_by! {|m| m.published_date}
#=> [#Document1, #Document2, etc]

If you want to know more about creating your own presenters, might I suggest the excellent RailsCast about it http://railscasts.com/episodes/287-presenters-from-scratch

I personally use the Draper library for presenters: https://github.com/drapergem/draper which makes presenting ActiveRecord objects a breeze. There's a RailsCast about it here: http://railscasts.com/episodes/286-draper