IT.Signals

I’ve been chasing my tail for the past day trying to track down a problem I was having in serializing a hash that contained two of my custom classes. I have two custom classes:

class Menu
…
end

class Permissions
…
end

I then have an ActiveRecord class that stores instances of these two classes in a hash which is then saved to my database.

class Role < ActiveRecord::Base

  serialize :credentials
  …
  self.credentials[:permissions] = Permissions.new(self)
  self.credentials[:menu] = Menu.new(self)
  …
end

After saving the record to the database I could inspect the field and all the YAML code was present and accounted for, the problem was that when I went to retrieve the serialized field, instead of getting back a hash with my two custom classes (i.e. Menu and Permissions) I was getting both objects of class YAML::Object.

After pulling my hair out for some time, I traced into the Rails code and saw that YAML::Load(string) was being called to unserialize the data. I then went to the YAML site and read more about the library which I admit I have limited knowledge about. I figured out that for some reason YAML was not finding my custom class definitions which meant it used YAML::Object. So now it was a matter of finding out how to tell YAML about my classes.

After doing more searching on the net I came across these articles which gave me the information I needed:

http://yaml4r.sourceforge.net/doc/page/type_families.htm
http://dev.rubyonrails.org/ticket/7537

I was able to add the following code to my environment.rb which will ensure any ActiveRecord derived classes will be correctly serialized. I also added two require statements to environment.rb to make sure my custom (non ActiveRecord derived) classes where also correctly serialized.

require ‘permissions’
require ‘menu’

…

YAML.add_domain_type("ActiveRecord,2007", "") do |type, val|
  klass = type.split(’:').last.constantize
  YAML.object_maker(klass, val)
end

class ActiveRecord::Base
  def to_yaml_type
    "!ActiveRecord,2007/#{self.class}"
  end
end

class ActiveRecord::Base
  def to_yaml_properties
    [’@attributes’]
  end
end

I restarted my server and everything worked !!!

I’ve always been slightly confused about when to use an ID and when to use a Class in my CSS. I’ve done some research which clarified my understanding.

The key thing to understand is that ID’s must be unique on a page and identifies a specific element, so you can only use a specified ID once per page. Classes on the other hand can be used multiple times on a page, if you are going to use a style that will be applied to multiple elements then use a Class.

I start by looking at all the sections and subsections on the page and how they work together. I identify all the unique sections on the page and define these with DIV’s and ID’s. Normally a page would consist of the following main sections:

#container { … }

#header { … }

#content { … }

#left { … }

#right { … }

#footer { … }

I then define all the child elements within each of these sections, so for example if I want the links in the header to be different to those in the content section I can easily do so. One of the main benefits of this approach is that when you look at the CSS file you can easily see why and where each style is being used.

#header a:link, #header a:visited {
color: red;
text-decoration: none;
font-weight: bold;
}

#content a:link, #content a:visited {
color: blue;
text-decoration: none;
font-weight: normal;
}

I define any shared look and feel styles using classes which I then use in different sections, In the case of the sidebar I have a left as well as a right sidebar, they have many look and feel things in common so I create a class called "sidebar" which defines the common styles. I share this common class between the left and right sidebar elements.

CSS:

.sidebar {
width: 170px;
margin: 0;
padding: 0;
}

.sidebar p {
font-size: 0.6em;
color: #555;
padding-left: 5px;
padding-top: 3px;}

#left {
float: left;
}

#right {
float: right;
}

HTML:

<div id="left" class="sidebar">
   <p>This is the left sidebar</p>
</div> <!– left –>

<div id="right" class="sidebar">
   <p>This is the right sidebar</p>
</div>

Another interesting point is that You are able to apply multiple classes to an element by space separating the classes, this allows an element to inherit multiple classes.

<DIV id="left" class="class1 class2 class3">Hello World!</DIV>

When there are errors on a form, Rails will normally create a <DIV> element with the fieldWithErrors class wrapped around the fields input statement. If you have your own CSS class wrapped around a field this will be overridden by the fieldWithErrors <DIV> which is a pain.

I was searching for a solution when I found this post:

I’d like to say I came up with this, but I actually found it somewhere else.

I have the following inside my environment.rb file:

ActionView::Base.field_error_proc = Proc.new do |html_tag, instance|
  msg = instance.error_message
  error_style = "background-color: #f2afaf"
  if html_tag =~ /<(input|textarea|select)[^>]+style=/
    style_attribute = html_tag =~ /style=[’"]/
    html_tag.insert(style_attribute + 7, "#{error_style}; ")
  elsif html_tag =~ /<(input|textarea|select)/
    first_whitespace = html_tag =~ /\s/
    html_tag[first_whitespace] = " style=’#{error_style}’ "
  end
  html_tag
end

I now get the desired effect when an error occurs, in my case it changes the background color of the field red, you can change it to whatever effect you want without it interfering with your field CSS classes…perfect!

I’m currently writing an article on Ruby’s approach to objects, classes and also the use of self. Coming from a C++ background it has taken me sometime to grasp the Ruby way of doing things.

I’m doing it for a number of reasons, I want to enforce in my own mind the things that I have been learning, I find writing them down helps a lot. I also want to use it as a reference in the future as I’m sure I’ll forgot things down the track, also someone else may find it useful.

So look for Part 1 in a few days.

Added some more plugins today:

• Optimal Title
• WordPress.com Stats

I’ve been wanting to setup a blog for a long time but never quite got around to it, until now. I’m using WordPress as it was compatible with the components on my host server, and seems very popular. It was simple to setup and install, I’m using a wonderful template developed by Tommaso Baldovino. I originally looked at  mephisto but the server that hosts this blog did not have the required components. I’ve installed a few plugins while I was setting it all up including:

• Akismet
• Category Cloud Widget
• WP-ContactForm
• Dean’s FCKEditor For Wordpress

I work as a freelance developer using a number of development tools including C++, PHP, Ruby, and Rails.