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<!DOCTYPE html><html lang="en"><head><meta charset="utf-8"><title>Class Factory: Factory_girl-like syntax for dynamically creating Ruby classes - Pat Shaughnessy</title><meta name="description" content=""><meta name="author" content=""><meta name="viewport" content="width=device-width, initial-scale=1"><link rel="stylesheet" href="/assets/css/normalize.css"><link rel="stylesheet" href="/assets/css/skeleton.css"><link rel="alternate" type="application/atom+xml" title="Pat Shaughnessy - Feed" href="http://feeds2.feedburner.com/patshaughnessy"><link rel="icon" type="image/png" href="images/favicon.png"></head><body><div id="banner"><a href="/"><span id="title">Pat Shaughnessy</span><span id="tagline"> blogger, rubyist, aspiring author</span></a></div><div style="margin-top: 35px"><div class="ten columns"><div class="container"><div class="row"><article class="post"><header><h1>Class Factory: Factory_girl-like syntax for dynamically creating Ruby classes</h1><div class="metadata">March 12th 2010&nbsp;&mdash;&nbsp;<a href="#disqus_thread" data-disqus-identifier="https://patshaughnessy.net/class_factory">&nbsp; Comments and &nbsp; Reactions</a></div></header><section class="content"><p>Class Factory will dynamically create classes using a factories model similar to <a href="http://github.com/thoughtbot/factory_girl">factory_girl</a>. But instead of passing a block with model attributes into the factory definition, you pass in a migration defining the attributes of the new model class you want to create:</p>
<div class="CodeRay">
  <div class="code"><pre><span class="co">ClassFactory</span>.define <span class="sy">:person</span> <span class="r">do</span> |p|
  p.string  <span class="sy">:first_name</span>
  p.string  <span class="sy">:last_name</span>
  p.integer <span class="sy">:age</span>
<span class="r">end</span></pre></div>
</div>
<p><br>Now when you need a &ldquo;Person&rdquo; class in your tests you create one like this:</p>
<div class="CodeRay">
  <div class="code"><pre><span class="co">ClassFactory</span> <span class="sy">:person</span>
=&gt; Person(id: integer, first_name: string, last_name: string, age: integer)</pre></div>
</div>
<p><br>This can be useful if you&#x27;re writing tests for a gem or plugin and don&#x27;t want to load the entire Rails environment, or have access to existing models in a target application. By default Class Factory creates ActiveRecord model classes, but using the :super option you can create any sort of Ruby class. Class Factory also makes it easy for each of your tests to use a different variation on a target class. For example, this will delete the Person model we created above, and create a new Person model that belongs to a group:</p>
<div class="CodeRay">
  <div class="code"><pre><span class="co">ClassFactory</span> <span class="sy">:person</span>, <span class="sy">:class_eval</span> =&gt; <span class="s"><span class="dl">'</span><span class="k">belongs_to :group</span><span class="dl">'</span></span> <span class="r">do</span> |p|
  p.string  <span class="sy">:first_name</span>
  p.string  <span class="sy">:middle_name</span>
  p.string  <span class="sy">:last_name</span>
  p.string  <span class="sy">:group_id</span>
<span class="r">end</span>
=&gt; Person(id: integer, first_name: string, middle_name: string, last_name: string,
   group_id: string)</pre></div>
</div>
<p><br>Creating different variations of the same class can be useful if you&#x27;re writing tests for a generator, plugin or some other code which has different behavior depending on what classes you run it against.</p>
<p><b>Options</b></p>
<p>Default: create a new ActiveRecord model, along with a corresponding table in your database:</p>
<div class="CodeRay">
  <div class="code"><pre><span class="co">ClassFactory</span> <span class="sy">:person</span></pre></div>
</div>
<p><br>Execute a migration on the new table specified as a block, defining the attributes of the new model class:</p>
<div class="CodeRay">
  <div class="code"><pre><span class="co">ClassFactory</span> <span class="sy">:person</span> <span class="r">do</span> |p|
  p.string  <span class="sy">:first_name</span>
  p.string  <span class="sy">:last_name</span>
  p.integer <span class="sy">:age</span>
<span class="r">end</span></pre></div>
</div>
<p><br>Create a class with a specified superclass (default is ActiveRecord::Base):</p>
<div class="CodeRay">
  <div class="code"><pre><span class="co">ClassFactory</span> <span class="sy">:person_array</span>, <span class="sy">:super</span> =&gt; <span class="co">Array</span></pre></div>
</div>
<p><br>If the super class is not a subclass of ActiveRecord::Base then Class Factory won&#x27;t create a table or run a migration. You can use this to create plain Ruby object classes.</p>
<p>Create a class called &ldquo;DifferentClass&rdquo; instead of &ldquo;Person:&rdquo;</p>
<div class="CodeRay">
  <div class="code"><pre><span class="co">ClassFactory</span> <span class="sy">:person</span>, <span class="sy">:class</span> =&gt; <span class="s"><span class="dl">'</span><span class="k">DifferentClass</span><span class="dl">'</span></span></pre></div>
</div>
<p><br>Run the given code inside the new class using class_eval:</p>
<div class="CodeRay">
  <div class="code"><pre><span class="co">ClassFactory</span> <span class="sy">:person</span>, <span class="sy">:class_eval</span> =&gt; <span class="s"><span class="dl">'</span><span class="k">has_many :shoes</span><span class="dl">'</span></span></pre></div>
</div>
<p><br>Create a table with the given name, instead of a table called &ldquo;people:&rdquo;</p>
<div class="CodeRay">
  <div class="code"><pre><span class="co">ClassFactory</span> <span class="sy">:person</span>, <span class="sy">:class_eval</span> =&gt; <span class="s"><span class="dl">'</span><span class="k">set_table_name :table_name</span><span class="dl">'</span></span>,
             <span class="sy">:table</span> =&gt; <span class="s"><span class="dl">'</span><span class="k">table_name</span><span class="dl">'</span></span></pre></div>
</div>
<p><br>If you provide options when the factory is defined they will be applied to each class created with the factory. You can also provide options when you create a class, in which case they will override the factory options.</p>
<p><b>Install</b></p>
<div class="CodeRay">
  <div class="code"><pre>gem install class_factory</pre></div>
</div>
<p><b><br>Code</b></p>
<a href="http://github.com/patshaughnessy/class_factory">http://github.com/patshaughnessy/class_factory</a>
<p><b><br>Detailed Example</b></p>
<p>Start an irb session and require class_factory (this will also require active_record):</p>
<div class="CodeRay">
  <div class="code"><pre>$ irb
&gt; require 'rubygems'
=&gt; true
&gt; require 'class_factory'
=&gt; true</pre></div>
</div>
<p><br>Create an in-memory SQLite test database:</p>
<div class="CodeRay">
  <div class="code"><pre>&gt; ActiveRecord::Base.establish_connection({ :adapter =&gt; 'sqlite3',
  :database =&gt; ':memory:' })
=&gt; #&lt;ActiveRecord::ConnectionAdapters::ConnectionPool:0x19cfecc...</pre></div>
</div>
<p><br>Define a person class factory, and create a Person class:</p>
<div class="CodeRay">
  <div class="code"><pre>&gt; ClassFactory.define :person do |p|
&gt;   p.string  :first_name
&gt;   p.string  :last_name
&gt;   p.integer :age
&gt; end
=&gt; #&lt;ClassFactory:0x19c6fac @definition={:name=&gt;:person, :migration=&gt;...
&gt; ClassFactory :person
=&gt; Person(id: integer, first_name: string, last_name: string, age: integer)</pre></div>
</div>
<p><br>Now create an instance of a Person and count how many records we have in our test database:</p>
<div class="CodeRay">
  <div class="code"><pre>&gt; Person.create :first_name =&gt; 'Barack', :last_name =&gt; 'Obama', :age =&gt; 48
=&gt; #&lt;Person id: 1, first_name: &quot;Barack&quot;, last_name: &quot;Obama&quot;, age: 48&gt;
&gt; Person.count
=&gt; 1</pre></div>
</div>
<p><br>Next redefine the Person class and override the options set in the factory above; this time it will belong to a group. Note that the existing people table will be dropped and a new, empty people table created:</p>
<div class="CodeRay">
  <div class="code"><pre>&gt; ClassFactory :person, :class_eval =&gt; 'belongs_to :group' do |p|
&gt;   p.string  :first_name
&gt;   p.string  :middle_name
&gt;   p.string  :last_name
&gt;   p.string  :group_id
&gt; end
=&gt; Person(id: integer, first_name: string, middle_name: string, last_name: string,
   group_id: string)
&gt; Person.count
=&gt; 0</pre></div>
</div>
<p><br>Create a group class that has many people:</p>
<div class="CodeRay">
  <div class="code"><pre>&gt; ClassFactory.define :group, :class_eval =&gt; 'has_many :people' do |g|
&gt;   g.string :name
&gt; end
=&gt; #&lt;ClassFactory:0x18a05d8 @definition={:class_eval=&gt;&quot;has_many :people&quot;, ...
&gt; ClassFactory :group
=&gt; Group(id: integer, name: string)</pre></div>
</div>
<p><br>Finally, recreate the Barack person record and add him to the &ldquo;presidents&rdquo; group:</p>
<div class="CodeRay">
  <div class="code"><pre>&gt; g = Group.create :name =&gt; 'Presidents'
=&gt; #&lt;Group id: 1, name: &quot;Presidents&quot;&gt;
&gt; p = Person.new :first_name =&gt; 'Barack', :last_name =&gt; 'Obama', :age =&gt; 48,
  :group =&gt; g
=&gt; #&lt;Person id: nil, first_name: &quot;Barack&quot;, last_name: &quot;Obama&quot;, group_id: 1,
            age: 48&gt;
&gt; p.save
=&gt; true
&gt; g.people
=&gt; [#&lt;Person id: 1, first_name: &quot;Barack&quot;, last_name: &quot;Obama&quot;, group_id: &quot;1&quot;,
   age: 48&gt;]</pre></div>
</div>
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