Notetagger - Adding tags

Onwards to implementing tagging, taking advantage of a whole bunch of Ruby on Rails features: Helpers, assocations, partials, and filters.

I wasn’t entirely sure how to go about the whole tagging business, and I initially went for keeping all the tags separated by spaces in a string. While that’s a perfectly fine way to display and enter tags, it has a whole bunch of flaws when you actually want to store and use the tags.

(You might want to read the previous installment before this one.)

But then what?

I decided to just go ahead with the most obvious implementation I could think of, where a note has many tags, and a tag has many notes – ie a has_and_belongs_to_many association in ActiveRecord dialect.

First the database table for storing tags:

CREATE TABLE tags (
    id INT NOT NULL AUTO_INCREMENT ,
    name VARCHAR(255),
    PRIMARY KEY ( id )
);

And the required table to manage the join between notes and tags:

CREATE TABLE notes_tags (
    note_id INT NOT NULL,
    tag_id INT NOT NULL,
    FOREIGN KEY (note_id) REFERENCES notes ON UPDATE CASCADE ON DELETE CASCADE,
    FOREIGN KEY (tag_id) REFERENCES tags ON UPDATE CASCADE ON DELETE CASCADE
);

I also needed a model for the tags:

> script\generate model Tag

I can now inform the Notes model that it actually has a bunch of tags associated with it (not that any note actually has at the moment, but we’ll get around to that):

class Note < ActiveRecord::Base
  has_and_belongs_to_many :tags
end

When I create or update a note, I am going to be entering the tags as a long, space separated string. I want to store that string in Note.tag_string, but I also want to update the notes_tags join table. I opted to do this by using an after_save filter in the Note model:

class Note < ActiveRecord::Base
  ...  
  after_save :update_tags  
  # Maintains the tag associations
  def update_tags    
    self.tags.clear
    for tag_name in self.tag_string.split      
      tag = Tag.new(:name => tag_name) unless (tag = Tag.find_by_name(tag_name))
      self.tags.push(tag)
    end
  end
end

Basically what this does, is whenever the Note has been saved – ie created or updated – the tag_string is split into individual tagnames. Each tagname is then found in the tags table if it exists – if it doesn’t, the tag gets created.

Finally it populates the Note.tags association with the tag we either just created or found. tags.push(tag) inserts and updates the relevant rows in both the tags and the notes_tags tables.

Listing them tags

What fun would a bunch of tags be if there was no way to list them? That’s right, not much fun at all! So let’s list them.

The taglist is basically a list of all the tags in the database. It should be usable from every view, so this sounds like a good match for a partial. Creating a new view, app/views/tags/_list.rhtml, allows me to put

<%= render_partial 'tags/list' %>

wherever I want the list of tags displayed. The view itself is straightforward:

<% @tags = Tag.find_all(nil, 'name') %>
<% if @tags.size > 0 %>
<ul>
	<% for tag in @tags %>
		<li><%= tag.name %></li>
	<% end %>
</ul>
<% end %>

However, the above isn’t quite enough. I want to be able to show how many notes have been tagged with a given tag, and ultimately to render the list as a weighted list. First things first, though:

To get the amount of notes for a given tag, I need to instruct the Tag that it is associated with Notes:

class Tag < ActiveRecord::Base
  has_and_belongs_to_many :notes
end

That’s it, I can now do tag.notes.size to get the amount.

Linking them tags

I now have a mighty fine list of tags and the amount of notes that exist for that tag, but I want to list those notes. Instead of adding a sparkingly new tags controller with a notes action, I am going to add a tag action to the existing notes controller:

class NotesController < ApplicationController
  ...
  def tag
    @tag = Tag.find_by_name(@params[:id])    
    @notes = @tag.notes
    render 'notes/list'
  end
end

I don’t even need to create a new view for this action, since I can simply use the app/views/notes/list.rhtml already created.

So I have a list of tags, and an URL where I list notes with a given tag. How about linking those? Why Jakob, that’s a great idea – back to the app/views/tags/_list.rhtml partial.

Doing the immediate, simple thing first I change the part inside the <li></li> to

<%= link_to "#{tag.name} (#{tag.notes.size})", :action => 'tag', :id => tag.name %>

and sure enough, that gives me a link to the tags action. However, looking at my list of notes I notice I am linking to tags in more than one place, and I figure it’d be grand if I didn’t have to put the above link_to snippet in every instance. Enter ApplicationHelper.

The above snippet transmogriffed into a helper function in app/helpers/application_helper.rb:

def link_to_tag(tag)
  return link_to "#{tag.name} (#{tag.notes.size})", :action => 'tag', :id => tag.name
end

which allows me to do

link_to_tag TagObject

whenever I want a link to a tag, nice! But not nice enough.

Since I know I am aiming for a weighted list, I want to be able to add CSS classes to the links that indicate their “weight”. For now, I define weight as a number from 0 to 9, and calculate it based on the amount of notes a tag has. To do that, I need to know the amount of total tags in the system, so I’ll pass that to the helper and have it act accordingly:

def link_to_tag(tag, total_tags = nil)    
  if total_tags.nil?  
    return link_to "#{tag.name} (#{tag.notes.size})", :action => 'tag', :id => tag.name
  else
    level = ((tag.notes.size * 10) / total_tags).to_i
    return link_to "#{tag.name}", {:action => 'tag', :id => tag.name}, :class => "level#{level}"
  end
end

I am pretty sure I’ll end up with some screwy results if there’s only one or two tags and a lot of posts, but the above works for my purposes so far. I can always fix screwy results when they actually surface.

But that’s it for tags for now: Notes can be tagged and displayed by their tag, and I can add a list of tags wherever I want it.

Continue to Adding the AJAX