使增量函数起作用的正确方法是什么？

Question

I'm creating a website that let people read short stories in several chapters. For this, I nested a chapter scaffold inside a novel scaffold, and linked (novel has_many :chapters, chapters belongs_to :novel) them both together. However I'm trying to get the chapter's number inside the URL (instead of the id, which never decreases). Setting the chapter as is is not a problem, but I'd like to automate the chapter number without my users needing to add it themselves.

To do so, I figured that all I needed was to get how many chapter the current novel had by checking self.class.where(:novel_id => @novel).count . At this point, I have no issues, however it gets complicated when I try to increment this number, I get the error: undefined method 'anoter_one' for 0:Fixnum

Here is my "another_one" function inside my model (I tried some things)

  def another_one
    @number = self.class.where(:novel => @novel).count.to_i
    @number.increment
  end

Here is the controller

  def create
    @novel = Novel.find(params[:novel_id])
    @chapter = Chapter.new(chapter_params)
    @chapter.chapter_number.another_one
    @chapter.novel = @novel
    if @chapter.save
      redirect_to novel_chapter_path(@novel, @chapter), notice: 'Chapter was successfully created.'
    else
      render :new
    end
  end

What am I doing wrong ?

Thank you in advance

Answer 1

Your calling anoter_one - which is a misspelling of another on the value of @chapter.chapter_number - not the model.

One way to solve this is by using an association callback :

class Novel
  has_many :chapters, before_add: :set_chapter_number
  def set_chapter_number(chapter)
    if chapter.chapter_number.blank? 
      chapter.chapter_number = self.chapters.size + 1
    end
  end
end

In order for the callback to be called properly you want to build the associated items off the parent:

def new
  @novel = Novel.find(params[:novel_id])
  @chapter = @novel.chapters.new
end

def create
  @novel = Novel.find(params[:novel_id])
  @chapter = @novel.chapters.new(chapter_params)

  if @chapter.save
    redirect_to [@novel, @chapter], notice: 'Chapter was successfully created.'
  else
    render :new
  end
end