From: James Edward Gray II <james@...>
Date: 2006-08-02T22:57:49+09:00
Subject: Re: Can you explain what this repo (yaml/Marshal) code do?

On Aug 2, 2006, at 5:35 AM, anne001 wrote:

>> It looks like in this code, this is simply how the save and load
>> functions are implemented, and since 'self' is being passed, it will
>> just serialize the Repository object to file during save and restore
>> it during load.
>
> but why do you need to save and load the objects,
> I have never seen code like this before. What do you gain?
> what is the problem that it resolves

Well, let's pretend you had some wiki class in your code:

     # a mock wiki object...
     class WikiPage
       def initialize( page_name, author, contents )
         @page_name = page_name
         @revisions = Array.new

         add_revision(author, contents)
       end

       attr_reader :page_name

       def add_revision( author, contents )
         @revisions << { :created  => Time.now,
                         :author   => author,
                         :contents => contents }
       end

       def wiki_page_references
         [@page_name] + @revisions.last[:contents].scan(/\b(?:[A-Z]+ 
[a-z]+){2,}/)
       end

       # ...
     end

Now, let's assume you have a Hash of these things you are using to  
run your wiki:

     wiki = Hash.new
     [ ["HomePage", "James", "A page about the SillyEmailExamples..."],
       ["SillyEmailExamples", "James", "Blah, blah, blah..."] ].each  
do |page|
       new_page = WikiPage.new(*page)
       wiki[new_page.page_name] = new_page
     end

When your script runs you will need to save these pages to a disk  
somehow, so you don't lose the site contents between runs.  You have  
a ton of options here, of course, including using a database or  
rolling some method that can write these pages out to files.

Writing them out is a pain though because page contents can be pretty  
much anything, so you'll need to come up with a good file format that  
allows you to tell where each revision starts and stops.  This  
probably means handling some escaping characters of some kind, at the  
minimum.

Or, you can just use Marshal/YAML.  With these helpers, saving the  
entire wiki is reduced to the trivial:

     File.open("wiki.dump", "w") { |file| Marshal.dump(wiki, file) }

When needed, you can load that back with:

     wiki = File.open("wiki.dump") { |file| Marshal.load(file) }

Those files will be stored in a binary format for Ruby to read.  If  
you would prefer a human-readable format, replace the word Marshal  
with YAML above and make sure your script does a:

   require "yaml"

See how easy it is to get instant saving/loading of entire Ruby  
structures?

James Edward Gray II