如何使用引入nokogiri

Question

require 'rubygems' 
require 'nokogiri' 
require 'open-uri' 
url = 'https://www.trumba.com/calendars/smithsonian-events.xml' 
doc = Nokogiri::XML(open url) 

我试图获取基本设置信息等解析页面的HTML内容：

event_name 
categories 
sponsor 
venue 
event_location 
cost 

例如，对于event_name我有这样的XPath：

"/html/body/div[2]/div[2]/div[1]/h3/a/span" 

而且使用它像：

puts doc.xpath "/html/body/div[2]/div[2]/div[1]/h3/a/span" 

这将返回零为event_name。

如果我在本地保存URL内容，那么上面的XPath就可以工作。

除此之外，我还需要上述信息。我也检查了其他XPath，但结果变成空白。

Answer 1

提供的链接包含XML，因此您的XPath表达式应该与XML结构一起工作。

关键是文档具有名称空间。据我了解，所有的XPath表达式都应该记住并且指定命名空间。
为了简单的XPath表达式可以使用remove_namespaces!方法：

require 'nokogiri' 
require 'open-uri' 
url = 'https://www.trumba.com/calendars/smithsonian-events.xml' 
doc = Nokogiri::XML(open(url)); nil # nil is used to avoid huge output 

doc.remove_namespaces!; nil 
event = doc.xpath('//feed/entry[1]') # it will give you the first event 

event.xpath('./title').text # => "Conservation Clinics" 
event.xpath('./categories').text # => "Demonstrations,Lectures & Discussions" 

最有可能你想拥有的所有事件哈希阵列。
你可以不喜欢它：

doc.xpath('//feed/entry').reduce([]) do |memo, event| 
    event_hash = { 
    title: event.xpath('./title').text, 
    categories: event.xpath('./categories').text 
    # all other attributes you need ... 
    } 
    memo << event_hash 
end 

它会给你一个数组，如：

[ 
    {:title=>"Conservation Clinics", :categories=>"Demonstrations,Lectures & Discussions"}, 
    {:title=>"Castle Highlights Tour", :categories=>"Gallery Talks & Tours"}, 
    ... 
] 

Answer 2

这是我怎么会去这样做：

require 'nokogiri' 
doc = Nokogiri::XML(open('/Users/gferguson/smithsonian-events.xml')) 
namespaces = doc.collect_namespaces 

entries = doc.search('entry').map { |entry| 
    entry_title = entry.at('title').text 
    entry_time_start, entry_time_end = ['startTime', 'endTime'].map{ |p| 
    entry.at('gd|when', namespaces)[p] 
    } 
    entry_notes = entry.at('gc|notes', namespaces).text 

    { 
    title: entry_title, 
    start_time: entry_time_start, 
    end_time: entry_time_end, 
    notes: entry_notes 
    } 

} 

，当运行结果为entries是哈希阵列：

require 'awesome_print' 
ap entries [0, 3] 

# >> [ 
# >> [0] { 
# >>  :title  => "Conservation Clinics", 
# >>  :start_time => "2016-11-09T14:00:00Z", 
# >>  :end_time => "2016-11-09T17:00:00Z", 
# >>  :notes  => "Have questions about the condition of a painting, frame, drawing,\n print, or object that you own? Our conservators are available by\n appointment to consult with you about the preservation of your art.\n \n To request an appointment or to learn more,\n e-mail DWRCLunder@si.edu and specify CLINIC in the subject line." 
# >> }, 
# >> [1] { 
# >>  :title  => "Castle Highlights Tour", 
# >>  :start_time => "2016-11-09T14:00:00Z", 
# >>  :end_time => "2016-11-09T14:45:00Z", 
# >>  :notes  => "Did you know that the Castle is the Smithsonian’s first and oldest building? Join us as one of our dynamic volunteer docents takes you on a tour to explore the highlights of the Smithsonian Castle. Come learn about the founding and early history of the Smithsonian; its original benefactor, James Smithson; and the incredible history and architecture of the Castle. Here is your opportunity to discover the treasured stories revealed within James Smithson's crypt, the Gre... 
# >> }, 
# >> [2] { 
# >>  :title  => "Exhibition Interpreters/Navigators (throughout the day)", 
# >>  :start_time => "2016-11-09T15:00:00Z", 
# >>  :end_time => "2016-11-09T15:00:00Z", 
# >>  :notes  => "Museum volunteer interpreters welcome visitors, answer questions, and help visitors navigate exhibitions. Interpreters may be stationed in several of the following exhibitions at various times throughout the day, subject to volunteer interpreter availability. <ul> \t<li><em>The David H. Koch Hall of Human Origins: What Does it Mean to be Human?</em></li> \t<li><em>The Sant Ocean Hall</em></li> </ul>" 
# >> } 
# >> ] 

我没有试图收集您所要求的具体信息，因为event_name不存在，您所做的事情非常通用，一旦理解了一些规则就可以轻松完成。

XML通常非常重复，因为它代表了数据表。表格的“单元格”可能会有所不同，但您可以使用重复来帮助您。在此代码中

doc.search('entry') 

通过<entry>节点循环。然后，很容易查看它们以找到所需的信息。

XML使用名称空间来帮助避免标记名称冲突。起初，这些看起来确实很难，但Nokogiri为文档提供了collect_namespaces方法，该方法返回文档中所有命名空间的散列。如果您正在查找名称空间标签，请将该散列作为第二个参数传递。

Nokogiri允许我们使用XPath和CSS作为选择器。为了便于阅读，我几乎总是使用CSS。ns|tag是告诉Nokogiri使用基于CSS的命名空间标签的格式。再次，传递文档中名称空间的散列，Nokogiri将完成其余部分。

如果您熟悉使用Nokogiri，您会看到上面的代码与用于将<td>单元的内容拉到HTML <table>中的<tr>行的正常代码非常相似。

您应该可以修改该代码来收集所需的数据，而不会冒名称空间冲突的风险。