title: Concat three or more fields in doctrine
body: <p>Doctrine query builder allows me to concat two fields only.</p>
  
  <pre><code>class Expr {
  // ...
  public function concat($x, $y); // Returns Expr\Func
  </code></pre>
  
  <p>To concatenate 3 fields I use:</p>
  
  <pre><code>$qb-&gt;expr()-&gt;concat(
      'table.field1',
      $qb-&gt;expr()-&gt;concat('table.field2', 'table.field3')
  );
  </code></pre>
  
  <p>And the SQL will be:</p>
  
  <pre><code>CONCAT('table.field1', CONCAT('table.field2', 'table.field3'))
  </code></pre>
  
  <p>How to get <strong>one</strong> concat?</p>
  
  <p>When I try to call directly</p>
  
  <pre><code>new Expr\Func('CONCAT', array('table.field1', 'table.field2', 'table.field3'));
  </code></pre>
  
  <p>Executing query gives me an error</p>
  
  <blockquote>
    <p>[Syntax Error] line 0, col 237: Error: Expected Doctrine\ORM\Query\Lexer::T_CLOSE_PARENTHESIS, got ','</p>
  </blockquote>
  
  <p>Dumping DQL:</p>
  
  <pre><code>CONCAT('table.field1', 'table.field2', 'table.field3')
  </code></pre>
  
  <p>Dumping SQL using <em>$qb->getQuery()->getSQL()</em>:</p>
  
  <blockquote>
    <p>[Syntax Error] line 0, col 237: Error: Expected Doctrine\ORM\Query\Lexer::T_CLOSE_PARENTHESIS, got ','</p>
  </blockquote>