Simple, powerful factories for Sequel models
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lib/sequel Add README Jun 24, 2012

Sequel::Factory is a little RubyGem that lets you easily specify factories for your Sequel models. A factory is an object that knows how to generate an instance of a model. They are very useful in testing and development scenarios when you need to simulate the existence of real data in your system.

Sequel::Factory supports the following features:

  • Multiple factories per model, with different attributes
  • Inclusion of the attributes of one factory into another
  • Ability to configure the Sequel::Model method used by a factory to generate instances (defaults to create)
  • Ability to override factory-generated values on instance creation
  • Sequential attributes (e.g. auto-incrementing ids)

Also, the actual code is only ~100 lines of Ruby, so it should be fairly straightforward for you to understand.


Using RubyGems:

$ sudo gem install sequel-factory

From a local copy:

$ git clone git://
$ cd sequel-factory
$ rake package && sudo rake install


Sequel::Factory adds a factory method to Sequel::Model. You use this method to define your factories by passing a block and (optionally) a name. When you pass a block a new instance of Sequel::Factory is created.

You call a factory using Sequel::Model.make. Each time the factory is called its block is instance_eval'd in the context of the factory. The factory uses method_missing to catch all unknown method calls and their arguments, which should correspond to the names and values of attributes to use for the model.

This may sound a bit complex, but it works out to be very simple in practice.

User.factory do
  # self is User.factory (or User.factories[:default])

User.factory(:with_email) do
  # self is User.factory(:with_email)
  include_factory User.factory

user1 = User.make               # Has a "name" attribute
user2 = User.make(:with_email)  # Has both "name" and "email" attributes

The above example defines two factories on the User model: a "default" factory and another factory named :with_email. The :with_email factory includes the default factory (using Sequel::Factory#include_factory), which just means that all attributes defined in the default factory will also be set on instances that are generated with the :with_email factory in addition to any attributes it defines itself.

In the example above I'm using the helpful randexp gem to generate my factory values, but you can generate them however you like.

If you need to generate unique sequential values you can pass a block to the attribute name when you call it in the factory. Each time this block is called it takes an incrementing integer value as its argument. The return value of the block is used as the value of the attribute.

The following example defines a factory on the User model that is able to generate a new User object with unique id and handle attributes.

User.factory do
  id {|n| n }
  handle "user#{id}"


Copyright 2012 Michael Jackson

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

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