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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.


Starting off with a simple user model.

class User include DataMapper::Resource

property :id, Serial property :username, String property :email, String property :password, String end

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

  1. The /\w+/.gen notation is part of the randexp gem:
  2. 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.


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



The real power of sweatshop is generating working associations.

DataMapper.setup(:default, "sqlite3::memory:")

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 }}
  1. 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}


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


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.