Remove unused tag

src/AppBundle/Controller/Admin/BlogController.php

@@ -12,6 +12,7 @@
 namespace AppBundle\Controller\Admin;
 
 use AppBundle\Entity\Post;
+use AppBundle\Entity\Tag;
 use AppBundle\Form\PostType;
 use Sensio\Bundle\FrameworkExtraBundle\Configuration\Method;
 use Sensio\Bundle\FrameworkExtraBundle\Configuration\Route;
@@ -146,7 +147,10 @@ public function editAction(Post $post, Request $request)
 
         if ($form->isSubmitted() && $form->isValid()) {
             $post->setSlug($this->get('slugger')->slugify($post->getTitle()));
-            $entityManager->flush();
+            $entityManager->transactional(function ($entityManager) {
+                $entityManager->flush();
+                $this->getDoctrine()->getRepository(Tag::class)->cleanUnusedTags();
+            });
 
             $this->addFlash('success', 'post.updated_successfully');
 
@@ -176,14 +180,14 @@ public function deleteAction(Request $request, Post $post)
         }
 
         $entityManager = $this->getDoctrine()->getManager();
-
-        // Delete the tags associated with this blog post. This is done automatically
-        // by Doctrine, except for SQLite (the database used in this application)
-        // because foreign key support is not enabled by default in SQLite
-        $post->getTags()->clear();
-
-        $entityManager->remove($post);
-        $entityManager->flush();
+        $entityManager->transactional(function ($entityManager) use ($post) {
+            // Delete the tags associated with this blog post. This is done automatically
+            // by Doctrine, except for SQLite (the database used in this application)
+            // because foreign key support is not enabled by default in SQLite
+            $post->getTags()->clear();
+            $entityManager->remove($post);
+            $this->getDoctrine()->getRepository(Tag::class)->cleanUnusedTags();
+        });
 
         $this->addFlash('success', 'post.deleted_successfully');
 

src/AppBundle/Entity/Tag.php

@@ -5,7 +5,7 @@
 use Doctrine\ORM\Mapping as ORM;
 
 /**
- * @ORM\Entity()
+ * @ORM\Entity(repositoryClass="AppBundle\Repository\TagRepository")
  * @ORM\Table(name="symfony_demo_tag")
  *
  * Defines the properties of the Tag entity to represent the post tags.

src/AppBundle/Repository/TagRepository.php

@@ -0,0 +1,42 @@
+<?php
+
+/*
+ * This file is part of the Symfony package.
+ *
+ * (c) Fabien Potencier <[email protected]>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace AppBundle\Repository;
+
+use AppBundle\Entity\Post;
+use AppBundle\Entity\Tag;
+use Doctrine\ORM\EntityRepository;
+use Doctrine\ORM\Query\ResultSetMapping;
+
+/**
+ * This custom Doctrine repository contains some methods to about tags.
+ *
+ * See http://symfony.com/doc/current/book/doctrine.html#custom-repository-classes
+ */
+class TagRepository extends EntityRepository
+{
+    /**
+     * Remove unused Tag from the Database.
+     */
+    public function cleanUnusedTags()
+    {
+        $joinTable = $this->getEntityManager()->getClassMetadata(Post::class)->getAssociationMapping('tags')['joinTable']['name'];
+        $tagTable = $this->getClassMetadata()->getTableName();
+        $unused_tags = $this->getEntityManager()->createNativeQuery("
+            DELETE FROM `$tagTable` WHERE id IN 
+            (
+                SELECT t.id FROM `$tagTable` t
+                LEFT JOIN `$joinTable` j ON j.tag_id = t.id
+                WHERE j.tag_id IS NULL
+            )
+        ", new ResultSetMapping())->execute();
+    }
+}