How To: Build a Wiki with Ruby on Rails – Part 2

Back in Part 1 of Building a Wiki with Ruby on Rails, we built the core wiki engine.

Time to add some syntax formatting.

These days, I’m pretty enamored of Haml, it’s more like HTML (unlike many other formatting engines) and it’s fast to write (unlike many other formatting engines).

1. Install Haml

Haml installs as a gem…1
gem install --no-ri haml
and a plugin…
haml --rails path/to/your/wiki

2. Create Your Haml View

Open up app/views/show.html.erb
and convert it to Haml. Replacing it to:

%h1= @page.title.gsub('_', ' ')
= link_to('Edit', page_edit_path(:page_title => @page.title))
= link_to('History', page_history_path(:page_title => @page.title))
= "Last Updated #{time_ago_in_words(@page.revisions.last.created_on)} ago by #{Person.find(@page.revisions.last.person_id).name}"
%p= auto_link(@page.revisions.last.parsed_contents)

Now, your wiki should look exactly like it did before we plugged in Haml.

3. Add Haml Support for Revisions

Open up app/models/revision.rb and update def parsed_contents with:

def parsed_contents
contents = contents.gsub(/(w*_w*)/) {|match| "<a href='#{match.downcase}'>#{match.gsub('_', ' ')}</a>"}
h =

4. Try It Out

Load up a page in your wiki, click ‘edit’, and add in some simple Haml, something like:

%strong this should be bold

5. Add in Some More (non-Haml) Formatting

Once you’re comfortable with Haml, maybe add in some other simple formatting rules into revision.rb

#Auto-renders any image URL
contents = self.contents.gsub(/s(.*.(jpg|gif|png))s/, '<img src="1"/>')

# Bolds text inside asterisks
contents = contents.gsub(/*(.*)*/, '<strong>1</strong>')

# Wraps <code> around text inside '@'
contents = contents.gsub(/@(.*)@/, '<code>1</code>')

# Blockquotes text inside double-quotes
contents = contents.gsub(/s"(.*)"s/, '<blockquote>"1"</blockquote>')

# Italicizes text inside underscores
contents = contents.gsub(/s_(.*)_s/, '<em>1</em>')

6. Make it Better

After playing around with Haml and other formatting, you’ll quickly see some quirks – some room for improvement. Go for it, and let me know when you get something interesting.

1. Remember to vendor your gems.

How To: Build a Wiki with Ruby on Rails – Part 1

Here’s how to build a very simple Ruby on Rails-based wiki engine 1.

1. Create the Rails App

rails wiki
and cd wiki to get inside the app.
Remember: create your database (i.e. wiki_development) and update config/database.ymlappropriately

2. Generate the Scaffolding

There are 3 nouns in this wiki system: People, Pages, Revisions. Let’s create the models for each of them.
run script/generate scaffold Person
Now open up wiki/db/migrate/*_create_people.rb and add:
t.column "name", :string inside the create_table block to store the Person’s name.

Add Person.create :name => "First Person"
after the create_table block to give us an initial Person.

run script/generate scaffold Page
Now open up wiki/db/migrate/*_create_pages.rb and add:
t.column "title", :string inside the create_table to store the Page’s title and add
Page.create :title => "Home_Page" after the create_table block to give us an initial Page.

run script/generate scaffold Revision
Now open up wiki/db/migrate/*_create_revisions.rb and add:

# Reference to the Person that created the Revision
t.column "person_id", :integer

# The contents of the Revision
t.column "contents", :text

# Reference to the Page this Revision belongs to
t.column "page_id", :integer

3. Run the database migrations

rake db:migrate

4. Describe the relationships between the Models

People should be able to create many Revisions.
Open /app/models/person.rb and add – after the first line:
has_many :revisions

Pages should have many Revisions
Open /app/models/page.rb and add – after the first line:
has_many :revisions

Revisions should reflect they belong to both Pages and People
Open /app/models/revision.rb and add – after the first line:

belongs_to :page
belongs_to :person

5. Draw up the Routes

Open up config/routes.rb and update them to handle wiki-fied words. Copy the following after the map.resources block

map.root :controller => 'pages', :action => 'show', :id => 1

map.connect 'pages.:format', :controller => 'pages', :action => 'index'
map.connect 'revisions.:format', :controller => 'revisions', :action => 'index'

map.page_base ':title', :controller => 'pages', :action => 'show'
map.connect ':title.:format', :controller => 'pages', :action => 'show'

map.page_history ':title/history', :controller => 'pages', :action => 'history'
map.connect ':title/history.:format', :controller => 'pages', :action => 'history'

map.page_edit ':title/edit', :controller => 'pages', :action => 'edit'

Now run script/server and load up a browser.
If things are working correctly, you should see simply ‘Edit | Back’ as links

6. Create the Views

Open /app/views/revisions/new.html.erb and add

< %= f.text_area :contents %>

< % fields_for :person do |p| %>

< %= p.text_field :name %>

< % end %>

right after < %= f.error_messages %> for the Revision’s content, the corresponding Page and the author’s name
Loading up should give you the form with the text area, a text field, and a submit button you just created.

Try entering something into the form and click ‘Create’. You should see ‘Revision was successfully created.’ Now, if you pop into your database, you should see the new row in the Revisions table with the contents you entered, but NULL values for person_id and page_id.
Let’s remedy that.

Open /app/controllers/revisions_controller.rb and add this line right after the @revision declaration in both def new and def create

@revision.update_attribute('person_id', Person.find_or_create_by_name(params[:person][:name]).id)

Reload and re-fill out the form. After hitting ‘Create’ you should have another Revision record in your database with some digit in the person_id field

Now, let’s tie the Revision form we created to a Page.
Open up /app/views/revisions/new.html.erb and change the form_for to:
< % form_for @revision, :url => new_revision_path, :html => {:method => :post} do |f| %>

Next, right after < %= f.text_area :contents %> add:
< %= f.hidden_field :page_id, :value => %>

Now, rename /app/views/revisions/new.html.erb to /app/views/revisions/_new.html.erb. This turns the form into a partial, which is fine, because Revisions only exist within Pages, never on their own.
Next, replace everything in /app/views/pages/edit.html.erb with

<h1>Update "< %= @page.title.gsub('_', ' ') %>"</h1>
< %= render :partial => 'revisions/new' %>

If you load up right now, you’ll get a ‘Called id for nil’ error. That’s because the Revision partial is referencing @revision, which doesn’t exist in /pages. Yet.
Open up /app/controllers/pages_controller.rb and scroll to ‘def edit’.
Add @revision = @page.revisions.last || right after the @page declaration

Refreshing should now correctly render the form.
Fill it out, hit ‘Create’ and check the database. You should have a new record with a number in the page_id column.

But we can’t see it because doesn’t show anything.

Open up /app/views/pages/show.html.erb and add:

<h2>< %= @page.title.gsub('_', ' ') %></h2>
<p>< %= @page.revisions.last.contents %></p>
<p>last edited by < %= %> on < %= time_ago_in_words(@page.revisions.last.created_at) %> ago</p>

to the first line and save.

Refreshing should show the text you entered.

7. Update the Model, Controller, Views, and Routes to Acknowledge Wiki-fied Words (separated with an underscore ‘_’)

Open up /app/models/revision.rb and add:

def parsed_contents
contents = self.contents.gsub(/(w*_w*)/) {|match| "<a href='#{match.downcase}'>#{match.gsub('_', ' ')}</a>"}

Open up /app/controllers/pages_controllers.rb, find def show and change:
@page = Page.find(params[:id])

@page = Page.find_or_create_by_title(params[:title])
return redirect_to page_edit_url(:title => @page.title) if @page.revisions.empty?

Open up /app/controllers/revisions_controllers.rb, find def create and change each :
format.html... line to
format.html { redirect_to page_base_url(:page_title => }

Next, scroll down to def edit and change:
@page = Page.find(params[:id])
@page = Page.find_by_title(params[:title])

Now, in /app/views/pages/show.html.erb change the Edit link to build the new route:
< %= link_to 'Edit', page_edit_url(:title => @page.title) %> |

Lastly, in config/routes.rb, change
map.root :controller => 'pages', :action => 'show', :id => 1
map.root :controller => 'pages', :action => 'show', :title => 'Home_Page'

Restart your script/server and you should have a very basic wiki.

In Part 2, we’ll add formatting.

Want to see it in action? Play around with

1. There are leaner Ruby frameworks to build wikis in (Camping or Merb come to mind.). I picked Rails for 2 reasons; My servers and deployment process was already set up for Rails, I wanted to loosely integrate this wiki into another existing Rails-based application (

How Wikis Work Best

Hugh Macleod released the HughPage, a wiki for bloggers, yesterday. As always he concisely captures the power of a wiki.

“The Hughpage wiki is up and at your disposal….Just blogged about something that doesn’t have a section? Then create a new section by yourself. No need to ask first. Exactly.”

Like describing the idea of wikis in general, he concludes:

“This is either a totally great idea or a totally insane idea. Maybe a bit of both…”

(Yes, Working Pathways is listed in the Blog and Podcast Consultant sections.)

I’ve worked with wikis for project documentation and team communication. Their power is in their organic growth and how they put the responsibility of accuracy on the reader. When I talk with others about wikis, one question always arises:

What if somebody writes something that’s not good?

At the heart of a wiki lies 2 equal responsibilities;

  1. The Author is responsible for writing accurate, useful, and interesting things.
  2. The Reader is responsible for changing things to make them better.

For the most part, these 2 responsiblities quickly make a very comprehensive knowledge base. If for whatever reason they fail, there’s always rolling back to a previous version of the page.

On a related note, over at we’ve been playing with a wiki to create a Minnesota internet talent directory.