Generating permalink from string in Ruby

If you are creating Ruby on Rails application like a blog, you most probably want to generate URLs using post titles. It’s good practice, because search engines like keywords in URL, and it looks more human-readable. Just compare: http://example.com/posts/10 and http://example.com/posts/generating-permalinks-from-string (yeah, it’s long, but self-descriptive). Anyways, this is small post about converting a title to a permalink.

First thing I love in Ruby is an ability to extend classes with my own methods. I could just add method to_permalink to any string and then everywhere I could write something like @post.title.to_permalink. It’s amazing!

Here is my version of to_permalink method:

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class String
def to_permalink
result = strip_tags
# Preserve escaped octets.
result.gsub!(/-+/, '-')
result.gsub!(/%([a-f0-9]{2})/i, '--\1--')
# Remove percent signs that are not part of an octet.
result.gsub!('%', '-')
# Restore octets.
result.gsub!(/--([a-f0-9]{2})--/i, '%\1')

result.gsub!(/&.+?;/, '-') # kill entities
result.gsub!(/[^%a-z0-9_-]+/i, '-')
result.gsub!(/-+/, '-')
result.gsub!(/(^-+|-+$)/, '')
return result.downcase
end

private

def strip_tags
return clone if blank?
if index('<')
text = ''
tokenizer = HTML::Tokenizer.new(self)

while token = tokenizer.next
node = HTML::Node.parse(nil, 0, 0, token, false)
# result is only the content of any Text nodes
text << node.to_s if node.class == HTML::Text
end
# strip any comments, and if they have a newline at the end (ie. line with
# only a comment) strip that too
text.gsub(/[\n]?/m, '')
else
clone # already plain text
end
end
end

How it’s working? First thing you would see is a private method strip_tags. Yes, I know about ActionView::Helpers::TextHelper::strip_tags, and this is almost 100% copy of Rails version (the only difference is that my version always returns clone of the original string). I just don’t want to rely on the Rails library.

Then my method replaces all special characters with dashes (only octets like %A0 would be kept), and trims dashed from the beginning and the end of the string. Finally full string will be lowercased.

Of course, in your application you should check collisions (several posts which have the same title should have unique permalinks, for example you could append numbers starting from 1: hello, hello-1, hello-2, etc). This is not my goal to cover all difficulties you could face, it’s small post, do you remember?

Just for your pleasure, here are the RSpec tests for this method:

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describe 'String.to_permalink from extensions.rb' do
it 'should replace all punctuation marks and spaces with dashes' do
"!.@#$\%^&*()Test case\n\t".to_permalink.should == 'test-case'
end

it 'should preserve _ symbol' do
"Test_case".to_permalink.should == 'test_case'
end

it 'should preserve escaped octets and remove redundant %' do
'Test%%20case'.to_permalink.should == 'test-%20case'
end

it 'should strip HTML tags' do
'<a href="http://example.com">Test</a> case'.to_permalink.should == 'test-case'
end

it 'should strip HTML entities and insert dashes' do
'Test case'.to_permalink.should == 'test-case'
end

it 'should trim beginning and ending dashes' do
'-. Test case .-'.to_permalink.should == 'test-case'
end

it 'should not use ---aa--- as octet' do
'b---aa---b'.to_permalink.should == 'b-aa-b'
end

it 'should replace % with -' do
'Hello%world'.to_permalink.should == 'hello-world'
end

it 'should not modify original string' do
s = 'Hello, world%20'
s.to_permalink.should == 'hello-world%20'
s.should == 'Hello, world%20'

s = 'Hello'
s.to_permalink.should == 'hello'
s.should == 'Hello'
end
end

It’s funny, right?

demjan

said on May 18th, 2007 at 20:59 · Permalink

Да. ))
Интересно сколько займет ресурсов и как будет выглядеть реализация на php в свете недавнего обсуждения на харахабарачтототам

Dmytro Shteflyuk

said on May 18th, 2007 at 21:30 · Permalink

Да ровно столько же! Все эти войны Something vs. Something another — чистой воды треп людей, которым нечем заняться. При грамотном подходе код в любом языке будет лаконичным и эффективным. Вопрос в компактности и читабельности — это да, целиком ложится на совесть языка.

Вон в комментах к статье о подзапросах я приводил пример кода пхп. Да, задача не повседневная, но классическая, когда надо обработать выборку. И ну никак всего этого уродства не обойти. Можно размазать по коду, это да. Или вынести в отдельный файл и никому не показывать. Но оно останется. Потому что ПХП — это набор знаков препинания, разделенных словами.

said on May 19th, 2007 at 08:57 · Permalink

Аналога этому в не обьектном языке не напишешь:

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class String
def to_permalink
end
end
'string'.to_permalink

Только вроде такого

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function to_permalink ($name) {
}
to_permalink($post->title);

said on May 19th, 2007 at 12:41 · Permalink

Ну почему же. В C# 3.0 можно будет писать extension методы:

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public static class Extensions
{
public static String ToPermalink(this String s)
{
}
}

'Something'.ToPermalink();

Это не аналогия открытости классов руби, а просто синтаксический сахар. Но результаты в общем-то неразличимы невооруженным взглядом :-)

kelyar

said on June 4th, 2007 at 11:29 · Permalink

а почему просто не переопределить to_param модели?

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Generating permalink from string in Ruby

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