bug #460 Reduce DB query number in post index action (yceruto)

This PR was squashed before being merged into the master branch (closes #460).

Discussion
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Reduce DB query number in post index action

**Performance Issue**

After tags feature the blog index page performs one extra query for each post to fetches its related tags. This PR avoids that.

Other changes:
* Refactoring the Post repository methods to reuse paginator creation in the future.

Commits
-------

0c169ca Reduce DB query number in post index action

Author: javiereguiluz

src/AppBundle/Repository/PostRepository.php

@@ -25,33 +25,34 @@
  *
  * @author Ryan Weaver <[email protected]>
  * @author Javier Eguiluz <[email protected]>
+ * @author Yonel Ceruto <[email protected]>
  */
 class PostRepository extends EntityRepository
 {
     /**
-     * @return Query
+     * @param int $page
+     *
+     * @return Pagerfanta
      */
-    public function queryLatest()
+    public function findLatest($page = 1)
     {
-        return $this->getEntityManager()
+        $query = $this->getEntityManager()
             ->createQuery('
-                SELECT p
+                SELECT p, t
                 FROM AppBundle:Post p
+                LEFT JOIN p.tags t
                 WHERE p.publishedAt <= :now
                 ORDER BY p.publishedAt DESC
             ')
             ->setParameter('now', new \DateTime())
         ;
+
+        return $this->createPaginator($query, $page);
     }
 
-    /**
-     * @param int $page
-     *
-     * @return Pagerfanta
-     */
-    public function findLatest($page = 1)
+    private function createPaginator(Query $query, $page)
     {
-        $paginator = new Pagerfanta(new DoctrineORMAdapter($this->queryLatest(), false));
+        $paginator = new Pagerfanta(new DoctrineORMAdapter($query));
         $paginator->setMaxPerPage(Post::NUM_ITEMS);
         $paginator->setCurrentPage($page);