diffrent

Diffrent is a very simple way to do ActiveRecord version diffing. It provides a convenient interface to two other libraries (Diffy and Vestal Versions), combining their functionality.

It makes no assumption about what web framework you're using - it can be used in Sinatra, Padrino, Rails, or with no framework at all.

Installation:

gem install diffrent

In a Gemfile:

gem 'diffrent'

Usage

Let's say you've got a Post model, with a title and a body. You've already set up Vestal Versions, and your Post model looks like this:

class Post
  versioned
end

With this all set up, you'll get a new version every time you save a Post object instance. How to get the differences between arbitrary versions? This is where diffrent comes in.

After adding 'diffrent' to your Gemfile and running 'bundle install', you can change your Post model so it looks like this:

class Post
   versioned
   include Diffrent
end

This give you the ability to pick up changes between different versions of your Post objects. For example:

> @post = Post.create(:title => "Arnold says", :body => "What you talking about, Willis?")
> @post.body = "This is what Willis is talking about"
> @post.save # creates a new version

Now we can:

> @post.diff_for(:body, 1,2)

=> "<div class=\"diff\">\n  <ul>\n    <li class=\"del\"><del><strong>This is w</strong>hat <strong>Willis is</strong> talking about</del></li>\n    <li class=\"ins\"><ins><strong>W</strong>hat <strong>you</strong> talking about<strong>, Willis?</strong></ins></li>\n  </ul>\n</div>\n"

By default, you'll get back HTML in your diffs. There's a final options hash on the diff_for method call, so that you can pass a :format option to Diffy:

> # get back raw text
>   p.diff_for(:body, 1, 2, :format => :text)
=> "-This is what Willis is talking about\n\\ No newline at end of file\n+What you talking about, Willis?\n\\ No newline at end of file\n" 

> # get back coloured text
> p.diff_for(:body, 1, 2, :format => :color)
=> "\e[31m-This is what Willis is talking about\e[0m\n\\ No newline at end of file\n\e[32m+What you talking about, Willis?\e[0m\n\\ No newline at end of file\n"

You can also pass a format of nil to get back a raw Diffy object if you need one.

Using it in a web app

Here's one way to incorporate Diffrent into a webapp to provide a user interface for viewing change. It's a Padrino example, but Sinatra or Rails will be substantially the same.

First, you'll need a controller action:

get :view_differences, :map => "/posts/:id/view_differences/:old/:new" do
  @post = Post.find(params[:id])
  render 'posts/view_differences'
end

Your view code can then look like this (please excuse my awesome HTML):

<% new_version = params[:new].to_i %>
<% old_version = params[:old].to_i %>

<p>Title:
  <%= @post.diff_for(:title, old_version, new_version) %>
</p>
<p>Body:
  <%= @post.diff_for(:body, old_version, new_version) %>
</p>

<p>
  <% if @post.has_versions_before?(new_version) %>
      <%= link_to("<< earlier", 
          url(:posts, :view_differences, :id => @post.to_param, 
              :old => new_version - 2,
              :new => new_version - 1)) %>
  <% end %>

  <% if @post.has_versions_after?(new_version) %>
    <%= link_to("later >>", 
          url(:posts, :view_differences, :id => @post.to_param, 
              :old => new_version,
              :new => new_version + 1)) %>
  <% end %>
</p>

As you can see, it's a bit manual - it seemed best to make very few assumptions about how people will want to use this.

Because of the (wonderful and simple) way that Vestal Versions works, you can diff arbitrary versions using this controller action and view - for instance, hitting a route like /posts/1/view_differences/3/50 would give you a diff on the title and body for all revisions between r3 and r50.

Contributing to diffrent

Check out the latest master to make sure the feature hasn't been implemented or the bug hasn't been fixed yet
Check out the issue tracker to make sure someone already hasn't requested it and/or contributed it
Fork the project
Start a feature/bugfix branch
Commit and push until you are happy with your contribution
Make sure to add tests for it. This is important so I don't break it in a future version unintentionally.
Please try not to mess with the Rakefile, version, or history. If you want to have your own version, or is otherwise necessary, that is fine, but please isolate to its own commit so I can cherry-pick around it.