title: Adding default values to rails 4 migrations and updating existing records
body: <p>Recently I realized that none of my database columns have default values. If an object is instantiated and then saved, it might have <code>nil</code> values for any fields that aren't filled out.</p>
  
  <p>I can make it so that I explicitly initialize these values, but then I've got some places where two controllers are creating the same object, but I didn't think of moving that code into a separate module.</p>
  
  <p>I can also choose to update my migrations to specify default values, which seems cleaner.</p>
  
  <p>I've decided to go with migrations. It is not a good idea to edit old migrations, so I'm creating a new migration and specifying that I want to change certain columns.</p>
  
  <p>Looking at how I should change columns, I have determined that I will use this</p>
  
  <pre><code>def change
    change_column :products, :size, :default =&gt; 0
  end
  </code></pre>
  
  <p>Will this modify existing records that currently have <code>nil</code> set for those records?</p>