title: Rails database defaults and model validation for boolean fields
body: <p>In a Rails model I have an attribute <code>is_subscriber</code>, when I constructed a db migration to add this column to the database I specified the default value to be false:</p>
  
  <pre><code>t.boolean  "is_subscriber",   :default =&gt; false
  </code></pre>
  
  <p>I also specified in the model that this attribute needs to be present:</p>
  
  <pre><code>validates :is_subscriber, presence: true
  </code></pre>
  
  <p>So why do I get this error when I create a model instance without specifying this attribute?</p>
  
  <pre><code>2012-05-08T21:05:54+00:00 app[web.1]: ActiveRecord::RecordInvalid (Validation failed: Is subscriber can't be blank):
  </code></pre>