title: how to issue query for multi layers linked tables in symfony
body: <p>I have a question about how to issue the createQueryBuilder for multilayers linked tables.</p>
  
  <p>I have one table "City" with a column "country_id" linked to a table "Country". The "Country" table has a column "zone_id" linked to table "Zone".</p>
  
  <p>How can I generate the QueryBuilder for the SQL as follow?</p>
  
  <pre><code>Select * from City
  LEFT JOIN Country AS c ON City.country_id=c.id
  LEFT JOIN Zone AS z ON c.zone_id=z.id
  WHERE z.id In (1,2,3,4)
  </code></pre>
  
  <p>In my city entity and country entity, I have made the ManytoOne link relationships.</p>
  
  <p>In CityEntity.php</p>
  
  <pre><code> /**
   * @ORM\ManyToOne(targetEntity="AppBundle\Entity\Country",cascade={"persist"})
   * @ORM\JoinColumn(nullable=false)
   */
   private $country;
  </code></pre>
  
  <p>In CountryEntity.php</p>
  
  <pre><code>/**
   * @ORM\ManyToOne(targetEntity="AppBundle\Entity\Zone",cascade={"persist"})
   * @ORM\JoinColumn(nullable=false)
   */
  private $zone;
  </code></pre>