方法的 Ruby 条件参数 [英] Ruby Conditional argument to method

问题描述

我有一些基于 css 选择器提取数据的通用"方法，这些选择器在许多网站中通常是相同的.但是，我有另一种方法可以接受给定网站的 css 选择器作为参数.

I have some 'generic' methods that extract data based on css selectors that usually are the same in many websites. However I have another method that accept as argument the css selector for a given website.

如果没有传递 title_selector 参数，我需要调用 get_title 方法.我该怎么做?

I need to call the get_title method if title_selector argument is nos passed. How can I do that?

  def scrape(urls, item_selector, title_selector, price_selector,     image_selector)
    collection = []
    urls.each do |url|
      doc = Nokogiri::HTML(open(url).read) # Opens URL
      @items = doc.css(item_selector)[0..1].map {|item| item['href']} # Sets items
      @items.each do  |item| # Donwload each link and parse
        page = Nokogiri::HTML(open(item).read)
        collection << {
          :title   => page.css(title_selector).text, # I guess I need conditional here 
          :price  => page.css(price_selector).text
        }
      end
      @collection = collection
    end
  end

通用标题提取器

  def get_title(doc)
    if doc.at_css("meta[property='og:title']")
      title = doc.css("meta[property='og:title']")
    else doc.css('title')
      title = doc.at_css('title').text
    end
  end

推荐答案

在 page.css 调用中使用 or 运算符.如果 title_selector 为 false (nil)，它将调用 get_title.

Use an or operator inside your page.css call. It will call get_title if title_selector is falsey (nil).

:title => page.css(title_selector || get_title(doc)).text,

不过，我不确定 doc 在这种情况下实际上应该是什么.

I'm not sure what doc should actually be in this context, though.

编辑

鉴于您在下面的评论，我认为您可以重构 get_title 来处理所有逻辑.允许 get_title 采用可选的 title_selector 参数并将此行添加到您的方法的顶部:

Given your comment below, I think you can just refactor get_title to handle all of the logic. Allow get_title to take an optional title_selector parameter and add this line to the top of your method:

return doc.css(title_selector).text if title_selector

然后，我原来的行变成:

Then, my original line becomes:

:title => get_title(page, title_selector)

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