The error message `undefined method `attr' for nil:NilClass (NoMethodError)` indicates that the

Question

The error message `undefined method `attr' for nil:NilClass (NoMethodError)` indicates that the

I'm encountering an error in my CLI app with a specific method.

The method in question is:

def self.deal_page(input, product_url)
    self.open_deal_page(input)
    deal = {}
    html = open(@product_url)
    doc = Nokogiri::HTML(html)
    data = doc.text.strip
    deal[:name] = doc.css("h1").text.strip
    deal[:discription] = doc.css(".textDescription").text.strip
    @purchase_link = nil
    @purchase_link= doc.at_css("div.detailLeftColumn a.success").attr("href")
        if @purchase_link.nil?
         deal[:purchase] = @product_url
       else
         deal[:purchase] = @purchase_link
       end
     deal
  end

However, I am seeing the following error message:

/home/himachhag-45739/code/popular-deals-from-slickdeals.net-cli/lib/popular_deals/newdeals.rb:54:in `deal_page': undefined method `attr' for nil:NilClass (NoMethodError) 
        from /home/himachhag-45739/code/popular-deals-from-slickdeals.net-cli/lib/popular_deals/cli.rb:70:in `disply_deal'                                                 
        from /home/himachhag-45739/code/popular-deals-from-slickdeals.net-cli/lib/popular_deals/cli.rb:49:in `menu'                                                        
        from /home/himachhag-45739/code/popular-deals-from-slickdeals.net-cli/lib/popular_deals/cli.rb:9:in `call'                                                         
        from /home/himachhag-45739/code/popular-deals-from-slickdeals.net-cli/bin/popular-deals:10:in `<top (required)>'                                                   
        from /usr/local/rvm/gems/ruby-2.3.1/bin/popular-deals:22:in `load'                                                                                                 
        from /usr/local/rvm/gems/ruby-2.3.1/bin/popular-deals:22:in `<main>'                                                                                               
        from /usr/local/rvm/gems/ruby-2.3.1/bin/ruby_executable_hooks:15:in `eval'                                                                                         
        from /usr/local/rvm/gems/ruby-2.3.1/bin/ruby_executable_hooks:15:in `<main>'

I've attempted using xpath, at_css, unless, if..else, but without success. This error doesn't occur consistently, but I would like to resolve it entirely.

css ruby nokogiri open-uri

Answer 1

Answer №1

To tackle this issue, one approach is to adopt a cautious mindset:

@purchase_link = doc.at_css("div.detailLeftColumn a.success").try(:attr, "href")

deal[:purchase] = @purchase_link || @product_url

There are a few key points to bear in mind here. In Ruby, only nil and false are considered logically false, so the need to explicitly test for nil? is quite rare. The exception arises when you wish to differentiate between nil and false, which does not happen frequently.

In this scenario, either the at_css method yields some results or it doesn't. Consequently, the try call has no effect if nothing is retrieved. If a match is found, the try call proceeds to the next step. Subsequently, you can assign values using the simple logical || (or) operator to prioritize them.

Moreover, since this code resides within a class method, utilizing instance variables casually may lead to complications. If entities like purchase_link are solely utilized within this method, refrain from including the @ symbol to avoid persistence.

Another factor to be wary of is how your method is defined:

def self.deal_page(input, product_url)

This declaration introduces an argument named product_url, yet inside the function:

html = open(@product_url)

It references the class instance variable @product_url, which is dissimilar. This discrepancy might result in calling the open function with an incorrect variable.

Answer 2

To tackle this issue, one approach is to adopt a cautious mindset:

@purchase_link = doc.at_css("div.detailLeftColumn a.success").try(:attr, "href")

deal[:purchase] = @purchase_link || @product_url

There are a few key points to bear in mind here. In Ruby, only nil and false are considered logically false, so the need to explicitly test for nil? is quite rare. The exception arises when you wish to differentiate between nil and false, which does not happen frequently.

In this scenario, either the at_css method yields some results or it doesn't. Consequently, the try call has no effect if nothing is retrieved. If a match is found, the try call proceeds to the next step. Subsequently, you can assign values using the simple logical || (or) operator to prioritize them.

Moreover, since this code resides within a class method, utilizing instance variables casually may lead to complications. If entities like purchase_link are solely utilized within this method, refrain from including the @ symbol to avoid persistence.

Another factor to be wary of is how your method is defined:

def self.deal_page(input, product_url)

This declaration introduces an argument named product_url, yet inside the function:

html = open(@product_url)

It references the class instance variable @product_url, which is dissimilar. This discrepancy might result in calling the open function with an incorrect variable.

Answer 3

Answer №2

It seems like the error in your code is originating from this particular line:

@purchase_link= doc.at_css("div.detailLeftColumn a.success").attr("href")

The issue arises because the attr method cannot be called on a nil value. Please check if the element exists in the HTML.

To troubleshoot, you can print out the value of

doc.at_css("div.detailLeftColumn a.success")

For more detailed guidance, feel free to visit http://www.nokogiri.org/tutorials/.

Answer 4

It seems like the error in your code is originating from this particular line:

@purchase_link= doc.at_css("div.detailLeftColumn a.success").attr("href")

The issue arises because the attr method cannot be called on a nil value. Please check if the element exists in the HTML.

To troubleshoot, you can print out the value of

doc.at_css("div.detailLeftColumn a.success")

For more detailed guidance, feel free to visit http://www.nokogiri.org/tutorials/.

Answer 5

Answer №3

Let's pinpoint the issue at hand:

def self.process_page(data, url)
  ...
  content = open(@url)

The problem lies in using url as a parameter, but attempting to access @url.

If @url is empty or nil, calling open will result in an error. This suggests that @url must be defined elsewhere, possibly leading to the failure of the selector.

Your code exhibits other issues as well:

information[:title] = document.css("h2").text.strip
information[:description] = document.css(".content").text.strip

By utilizing css, you are receiving a NodeSet

document.css('h1').class # => Nokogiri::XML::NodeSet

Followed by text, which combines all text within the NodeSet. This approach may not always align with your expectations. Consider this:

require 'nokogiri'

doc = Nokogiri::HTML(DATA.read)
doc.css('h1').text # => "example"
doc.css('h1').map(&:text) # => ["ex", "ample"]

__END__
<html>
  <body>
    <h1>ex</h1>
    <h2>sample</h2>
    <h1>ample</h1>
    <h2>test</h2>
  </body>
</html>

doc.css('h1').text merges "ex" and "ample" into "example". Dealing with this concatenation aftermath can prove to be quite challenging.

It's advisable to utilize doc.css('h1').map(&:text), except for those rare instances where concatenation is actually needed. Haven't encountered such a scenario... ever.

Answer 6

Let's pinpoint the issue at hand:

def self.process_page(data, url)
  ...
  content = open(@url)

The problem lies in using url as a parameter, but attempting to access @url.

If @url is empty or nil, calling open will result in an error. This suggests that @url must be defined elsewhere, possibly leading to the failure of the selector.

Your code exhibits other issues as well:

information[:title] = document.css("h2").text.strip
information[:description] = document.css(".content").text.strip

By utilizing css, you are receiving a NodeSet

document.css('h1').class # => Nokogiri::XML::NodeSet

Followed by text, which combines all text within the NodeSet. This approach may not always align with your expectations. Consider this:

require 'nokogiri'

doc = Nokogiri::HTML(DATA.read)
doc.css('h1').text # => "example"
doc.css('h1').map(&:text) # => ["ex", "ample"]

__END__
<html>
  <body>
    <h1>ex</h1>
    <h2>sample</h2>
    <h1>ample</h1>
    <h2>test</h2>
  </body>
</html>

doc.css('h1').text merges "ex" and "ample" into "example". Dealing with this concatenation aftermath can prove to be quite challenging.

It's advisable to utilize doc.css('h1').map(&:text), except for those rare instances where concatenation is actually needed. Haven't encountered such a scenario... ever.

The error message `undefined method `attr' for nil:NilClass (NoMethodError)` indicates that the

Answer №1

Answer №2

Answer №3

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