title: Doctrine wants to "ALTER TABLE coo_users CHANGE id id VARCHAR(255) NOT NULL;" but wants to do this each time I update the schema
body: <p>If I do <code>bin/console doctrine:schema:update --force</code> the result is:</p>
  
  <blockquote>
    <p>Updating database schema...<br />
    Database schema updated successfully! "1" query was executed</p>
  </blockquote>
  
  <p>And this is done each time I run the <code>update</code> command.</p>
  
  <p>So, with <code>bin/console doctrine:schema:validate</code> I see that:</p>
  
  <blockquote>
    <p>[Mapping]  OK - The mapping files are correct.<br />
    [Database] FAIL - The database schema is not in sync with the current mapping file.</p>
  </blockquote>
  
  <p>The query Doctrine wants to execute is ever the same (<code>bin/console doctrine:schema:update --dump-sql</code>):</p>
  
  <pre><code>ALTER TABLE coo_users CHANGE id id VARCHAR(255) NOT NULL;
  </code></pre>
  
  <p><strong>What's happening? It seems Doctrine wants to do any modification as it wants to change the field <code>id</code> again to field <code>id</code>, each time, in an infinite modification.</strong></p>
  
  <p>THE MAPPING</p>
  
  <pre><code>/**
   * @ORM\Id
   * @ORM\Column(type="string", unique=true)
   * @ORM\GeneratedValue(strategy="IDENTITY")
   */
  protected $id;
  </code></pre>