dm-sweatshop

Overview

dm-sweatshop is a model factory for DataMapper. It makes it easy & painless to crank out complex pseudo random models — useful for tests and seed data. Production Goals:

• Easy generation of random models with data that fits the application domain.
• Simple syntax for declaring and generating model patterns.
• Add context to model patterns, allowing grouping and
• Effortlessly generate or fill in associations for creating complex models with few lines of code.

Examples

Starting off with a simple user model.

  class User
    include DataMapper::Resource</p>
property :id, Serial
property :username, String
property :email,    String
property :password, String
end
<p>

A fixture for the user model can be defined using the fixture method.

  User.fixture {{
    :username             => (username = /\w+/.gen),
    :email                => "#{username}@example.com",
    :password             => (password = /\w+/.gen),
    :pasword_confirmation => password</p>
<ol>
	<li>The /\w+/.gen notation is part of the randexp gem:</li>
	<li>http://github.com/benburkert/randexp/
  }}

Notice the double curly brace ({{), a quick little way to pass a block that returns a hash to the fixture method. This is important because it ensures the data is random when we generate a new instance of the model, by calling the block every time.

And here’s how you generate said model.

  User.generate

That’s it. In fact, it can even be shortened.

  User.gen

Associations

The real power of sweatshop is generating working associations.

  DataMapper.setup(:default, "sqlite3::memory:")</p>
class Tweet
include DataMapper::Resource

property :id, Serial
property :message,  String, :length => 140
property :user_id,  Integer
belongs_to :user
has n, :tags, :through => Resource
end

class Tag
include DataMapper::Resource
property :id, Serial
property :name, String
has n, :tweets, :through => Resource
end

class User
include DataMapper::Resource

property :id, Serial
property :username, String

has n, :tweets
end
DataMapper.auto_migrate!
User.fix {{
:username => /\w+/.gen,
:tweets   => 500.of {Tweet.make}
}}

Tweet.fix {{
:message => /[:sentence:]/.gen[0..140],
:tags    => (0..10).of {Tag.make}
}}
Tag.fix {{
:name => /\w+/.gen
}}

<ol>
	<li>now lets generate 100 users, each with 500 tweets.  Also, the tweet’s have 0 to 10 tags!
  users = 10.of {User.gen}

That’s going to generate alot of tags, way more than you would see in the production app. Let’s recylce some already generated tags instead.

  User.fix {{
    :username => /\w+/.gen,
    :tweets   => 500.of {Tweet.make}
  }}
  
  Tweet.fix {{
    :message => /[:sentence:]/.gen[0..140],
    :tags    => (0..10).of {Tag.pick}           #lets pick, not make this time
  }}
  
  Tag.fix {{
    :name => /\w+/.gen
  }}
  
  50.times {Tag.gen}
  
  users = 10.of {User.gen}

Contexts

You can add multiple fixtures to a mode, dm-sweatshop will randomly pick between the available fixtures when it generates a new model.

  Tweet.fix {{
    :message  => /\@#{User.pick.name} [:sentence:]/.gen[0..140],   #an @reply for some user
    :tags     => (0..10).of {Tag.pick}
  }}

To keep track of all of our new fixtures, we can even give them a context.

  Tweet.fix(:at_reply) {{
    :message  => /\@#{User.pick.name} [:sentence:]/.gen[0..140],
    :tags     => (0..10).of {Tag.pick}
  }}
  
  Tweet.fix(:conversation) {{
    :message  => /\@#{(tweet = Tweet.pick(:at_reply)).user.name} [:sentence:]/.gen[0..140],
    :tags     => tweet.tags
  }}

Overriding a fixture

Sometimes you will want to change one of your fixtures a little bit. You create a new fixture with a whole new context, but this can be overkill. The other option is to specify attributes in the call to generate.

  User.gen(:username => 'datamapper')  #uses 'datamapper' as the user name instead of the randomly generated word

This works with contexts too.

  User.gen(:conversation, :tags => Tag.all)       #a very, very broad conversation

Go forth, and populate your data.

Best Practices

Specs

The suggested way to use dm-sweatshop with test specs is to create a spec/spec_fixtures.rb file, then declare your fixtures in there. Next, require it in your spec/spec_helper.rb file, after your models have loaded.

  Merb.start_environment(:testing => true, :adapter => 'runner', :environment => ENV['MERB_ENV'] || 'test')

  require File.join(File.dirname(__FILE__), 'spec_fixtures')

Add the .generate calls in your before setup. Make sure to clear your tables or auto_migrate your models after each spec!

Possible Improvements

Enforcing Validations

Enforce validations at generation time, before the call to new/create.

  User.fix {{
    :username.unique  => /\w+/.gen,
    :tweets           => 500.of {Tweet.make}
  }}

Better Exception Handling

Smarter pick

Add multiple contexts to pick, or an ability to fall back if one context has no generated models.