has_ratings

Instalation

1) Install the plugin with script/plugin install git://github.com/fnando/has_ratings.git

2) Generate a migration with script/generate migration create_ratings and add the following code:

class CreateRatings < ActiveRecord::Migration
  def self.up
    create_table :ratings do |t|
      t.integer :rating, :default => 0, :null => false
      t.references :rateable, :polymorphic => true
      t.references :user
      t.timestamps
    end

    add_index :ratings, :rateable_type
    add_index :ratings, :rateable_id
    add_index :ratings, :user_id
  end

  def self.down
    drop_table :ratings
  end
end

3) Add two columns on each model you're going to use has_ratings: ratings_count and rating

class AddRatingToPhoto < ActiveRecord::Migration
  def self.up
    add_column :photos, :ratings_count, :integer,
      :default => 0, :null => false

    add_column :photos, :rating, :float,
      :precision => 3, 
      :scale => 2,
      :default => 0,
      :null => false

    add_index :photos, :rating
    add_index :photos, :ratings_count
  end

  def self.down
    remove_index :photos, :rating
    remove_column :photos, :rating

    remove_index :photos, :ratings_count
    remove_column :photos, :ratings_count
  end
end

4) Run the migrations with rake db:migrate

Usage

1) Add the method call has_rating to your model.

class Photo < ActiveRecord::Base
  has_ratings
end

2) Add this association on your User model:

class User < ActiveRecord::Base
  has_many :ratings
end

photo = Photo.find(:first)
user = User.find(:first)

photo.rate(:user => user, :rating => 1) # => <rating>
photo.rated?(user) # => true
photo.ratings # => [<rating>]
photo.rating! # => 0.0 (will skip rating cache)
photo.rating # => will use non-cached rating attribute
photo.ratings_count # => ratings count
photo.find_users_that_rated # => []
photo.find_rating_by_user(user) # => <rating>

# retrieve best rated objects (order by rating desc)
Photo.best_rated # => [<photo>]

# retrieve most rated objects (order by ratings_count desc)
Photo.most_rated # => [<photo>]

If you have has_paginate installed, you can paginate the users that rated a given item:

photo.find_users_that_rated(:page => 2)

Use this view helper to display the rating system:

<%= rating_stars photo, current_user, rate_photo_path(photo) %>

Is based on this article. You can get the stars image at http://f.simplesideias.com.br/stars.gif. The CSS you need:

ul.rating {
    width: 80px;
    height: 16px;
    margin: 0 10px 0 0;
    padding: 0;
    list-style: none;
    float:left;
    position: relative;
    background: url(../images/stars.gif) no-repeat 0 0;
}

ul.zero         { background-position: 0 0; }
ul.zero-half    { background-position: 0 -16px; }
ul.one          { background-position: 0 -32px; }
ul.one-half     { background-position: 0 -48px; }
ul.two          { background-position: 0 -64px; }
ul.two-half     { background-position: 0 -80px; }
ul.three        { background-position: 0 -96px; }
ul.three-half   { background-position: 0 -112px; }
ul.four         { background-position: 0 -128px; }
ul.four-half    { background-position: 0 -144px; }
ul.five         { background-position: 0 -160px; }

ul.rating li {
    cursor: pointer;
    float: left;
    text-indent: -999em;
}

ul.rated li {
    cursor: default;
}

ul.rating li a,
ul.rating li span {
    position: absolute;
    left: 0;
    top: 0;
    width: 16px;
    height: 16px;
    text-decoration: none;
    z-index: 200;
}

ul.rating li.one a, ul.rating li.one span       { left:0; }
ul.rating li.two a, ul.rating li.two span       { left:16px; }
ul.rating li.three a, ul.rating li.three span   { left:32px; }
ul.rating li.four a, ul.rating li.four span     { left:48px; }
ul.rating li.five a, ul.rating li.five span     { left:64px; }

ul.rating li a:hover {
    z-index: 2;
    width: 80px;
    height: 16px;
    overflow: hidden;
    left: 0;
    background: url(../images/stars.gif) no-repeat 0 0
}

ul.rating li.one a:hover    { background-position:0 -176px; }
ul.rating li.two a:hover    { background-position:0 -192px; }
ul.rating li.three a:hover  { background-position:0 -208px; }
ul.rating li.four a:hover   { background-position:0 -224px; }
ul.rating li.five a:hover   { background-position:0 -240px; }

NOTE: You should have a User model. Otherwise, this won't work!

Copyright (c) 2008 Nando Vieira, released under the MIT license