You ever write a named_scope and think hey framework, I already wrote a schema
– why are you bothering me with all this work?!
What about those times when you’re sitting behind the wheel of your ride and the warning flag is up because Johnny gave Jimmy a little too hard of a bump around turn number three and you are left wondering just how fast you should go? I mean sure you’re worried about Jimmy being ok and all, that sure was quite the spinout back there, but geez, this is the Quest For The Cup and your points total is not going to grow itself! Well the latter situation has had a pacecar for a while - and now the first one does too.
Pacecar
Pacecar is a plugin for rails
application which gives your ActiveRecord models a bunch of class methods based
(mostly) on database introspection. It looks at column names and types to
generate named_scope methods at load time which can be used in your app and
combined with other named_scopes as well.
| Pacecar (Racing) | Pacecar (Ruby gem) | |
| Communicates driving speed limit to automobile racers | Yes | No |
Provides named_scopes to ActiveRecord classes |
No | Yes |
| Does the boring work for you so you can have fun | Yes | Yes |
Scenario
Assume we have the following schema in a rails application…
class CreateSchema < ActiveRecord::Migration
def self.up
create_table :users, :force => true do |t|
t.boolean :admin, :default => false, :null => false
t.datetime :approved_at
t.datetime :rejected_at
t.string :first_name
t.string :last_name
t.text :description
t.timestamps
end
create_table :posts, :force => true do |t|
t.string :owner_type
t.integer :owner_id
t.string :publication_state
t.string :post_type
t.timestamps
end
create_table :comments, :force => true do |t|
t.integer :user_id
t.text :description
t.timestamps
end
end
end
This is a fairly basic scenario - most applications are not this simple. But, this is enough to get the point across, and the benefits really only grow as you add more tables and more models. Here’s how we might model this data (the unfamiliar methods are coming from pacecar and will be explained shortly).
class User < ActiveRecord::Base
has_many :posts, :as => :owner
has_many :comments
scopes_ranking :comments
end
class Post < ActiveRecord::Base
PUBLICATION_STATES = %w(Draft Submitted Rejected Accepted)
TYPES = %w(Free Open Private Anonymous PostModern)
belongs_to :owner, :polymorphic => true
scopes_state :publication_state
scopes_state :post_type, :with => TYPES
scopes_polymorph :owner
end
class Comment < ActiveRecord::Base
belongs_to :user
end
Usage
Ok, so you have a schema and you have some models. Now, what named_scope do you need? Here’s what you get for free, when the pacecar plugin is installed…
#Records where approved_at is not null, or where it is null…
User.approved_at_present
User.approved_at_missing
#Records where first_name is not null, or where it is null…
User.first_name_present
User.first_name_missing
#Records ordered by first_name (default to ‘asc’, can specify to override)…
User.by_first_name
User.by_first_name(:asc)
User.by_first_name(:desc)
#Records where an attribute matches a search term (column LIKE "%term%")…
User.first_name_matches('John')
#Records where an attribute starts or ends with a search term…
User.first_name_starts_with('A')
User.first_name_ends_with('a')
#Records where any non-state text or string column matches term…
User.search_for('test')
#Records where any of a list of columns match the term…
User.search_for 'test', :on => [:first_name, :last_name]
#Records where all of a list of columns match the term…
User.search_for 'test', :on => [:first_name, :last_name], :require => :all
#Records that are all admins or non-admins…
User.admin
User.not_admin
#Records approved before or after certain times…
User.approved_at_before(5.days.ago)
User.approved_at_after(4.weeks.ago)
#Records with approved_at in the past or future…
User.approved_at_in_past
User.approved_at_in_future
#Records with approved_at inside or outside of two times…
User.approved_at_inside(10.days.ago, 1.day.ago)
User.approved_at_outside(2.days.ago, 1.day.ago)
#Records with certain year, month or day…
User.approved_at_in_year(2000)
User.approved_at_in_month(01)
User.approved_at_in_day(01)
#Records with a duration (time delta between two columns) of,
#over or under a certain number of days…
User.with_duration_of(14, :approved_at, :rejected_at)
User.with_duration_over(14, :approved_at, :rejected_at)
User.with_duration_under(14, :approved_at, :rejected_at)
#First x records…
User.limited(10)
And by using those #scopes_* class methods in the models, we also get…
#Records which have an owner_type of User…
Post.for_owner_type(User)
#Records with the most and least associated records…
User.maximum_comments
User.minimum_comments
#Records which are in a particular state, or not in a state…
Post.publication_state_draft
Post.post_type_not_open
Installation
To get the latest pacecar straight from git as a rails plugin, you can do..
ruby script/plugin install git://github.com/thoughtbot/pacecar.git
Alternately you can use the gem version from github…
gem sources -a http://gems.github.com
sudo gem install thoughtbot-pacecar
..and then add a line like this to your config/environment.rb…
config.gem 'thoughtbot-pacecar',
:lib => 'pacecar',
:version => '>= 1.0.0',
:source => 'http://gems.github.com'
After installing pacecar with either of these methods you will be up and running with all the for free methods, and you’ll then be able to add in the class method calls for enabling the Polymorph, State and Ranking use cases.
Sample usage
Hey dev team, can you tell us how many users are active but dont have bios?
User.bio_missing.active.count
How many events have we had that last longer than a week?
Event.with_duration_over(7, :starts_at, :ends_at).count
Can I see the titles and authors of all the blog posts that we are scheduled to post in the future?
Post.published_at_in_future.collect { |p|
"#{p.title} #{p.user.name}"
}
Word of caution
Pacecar does a decent amount of method generation at load time - so if you’re opposed to having lots of methods you should be aware of that. You should also do an audit of the class methods you already have in place before installing pacecar, and make sure you’re not overwriting any of your own methods (named scopes or otherwise). Also, if you’re philosophically opposed to method generation … this does that.
Visit our Open Source page to learn more about our team’s contributions.
