diff --git a/core/modules/aggregator/lib/Drupal/aggregator/CategoryStorageController.php b/core/modules/aggregator/lib/Drupal/aggregator/CategoryStorageController.php
index 299113c..c693e36 100644
--- a/core/modules/aggregator/lib/Drupal/aggregator/CategoryStorageController.php
+++ b/core/modules/aggregator/lib/Drupal/aggregator/CategoryStorageController.php
@@ -98,4 +98,11 @@ public function isUnique($title, $cid = NULL) {
     return (empty($rows));
   }
 
+  /**
+   * {@inheritdoc}
+   */
+  public function loadAllCategories() {
+    return $this->database->query('SELECT c.cid, c.title FROM {aggregator_category} c ORDER BY title')->fetchAllKeyed();
+  }
+
 }
diff --git a/core/modules/aggregator/lib/Drupal/aggregator/CategoryStorageControllerInterface.php b/core/modules/aggregator/lib/Drupal/aggregator/CategoryStorageControllerInterface.php
index a4ab4db..ecfe0f2 100644
--- a/core/modules/aggregator/lib/Drupal/aggregator/CategoryStorageControllerInterface.php
+++ b/core/modules/aggregator/lib/Drupal/aggregator/CategoryStorageControllerInterface.php
@@ -66,5 +66,10 @@ public function delete($cid);
    */
   public function isUnique($title, $cid = NULL);
 
+  /**
+   * Loads all categories.
+   */
+  public function loadAllCategories();
+
 }
 
diff --git a/core/modules/aggregator/lib/Drupal/aggregator/FeedFormController.php b/core/modules/aggregator/lib/Drupal/aggregator/FeedFormController.php
index ef25376..58efa59 100644
--- a/core/modules/aggregator/lib/Drupal/aggregator/FeedFormController.php
+++ b/core/modules/aggregator/lib/Drupal/aggregator/FeedFormController.php
@@ -7,13 +7,52 @@
 
 namespace Drupal\aggregator;
 
+use Drupal\Core\Entity\EntityFormControllerInterface;
 use Drupal\Core\Entity\EntityFormControllerNG;
+use Drupal\Core\Entity\EntityStorageControllerInterface;
 use Drupal\Core\Language\Language;
+use Drupal\aggregator\CategoryStorageControllerInterface;
+use Symfony\Component\DependencyInjection\ContainerInterface;
+
 
 /**
  * Form controller for the aggregator feed edit forms.
  */
-class FeedFormController extends EntityFormControllerNG {
+class FeedFormController extends EntityFormControllerNG implements EntityFormControllerInterface {
+
+  /**
+   * The feed storage.
+   *
+   * @var \Drupal\Core\Entity\EntityStorageControllerInterface
+   */
+  protected $feedStorage;
+
+  /**
+   * The category storage controller.
+   *
+   * @var \Drupal\aggregator\CategoryStorageControllerInterface
+   */
+  protected $categoryStorageController;
+
+  /**
+   * Constructs a FeedForm object.
+   *
+   * @param \Drupal\Core\Entity\EntityStorageControllerInterface $feed_storage
+   *   The feed storage.
+   * @param \Drupal\aggregator\CategoryStorageControllerInterface $category_storage_controller
+   *   The category storage controller.
+   */
+  public function __construct(EntityStorageControllerInterface $feed_storage, CategoryStorageControllerInterface $category_storage_controller) {
+    $this->feedStorage = $feed_storage;
+    $this->categoryStorageController = $category_storage_controller;
+  }
+
+  public static function create(ContainerInterface $container) {
+    return new static(
+      $container->get('plugin.manager.entity')->getStorageController('aggregator_feed'),
+      $container->get('aggregator.category.storage')
+    );
+  }
 
   /**
    * Overrides Drupal\Core\Entity\EntityFormController::form().
@@ -63,11 +102,11 @@ public function form(array $form, array &$form_state) {
     // Handling of categories.
     $options = array();
     $values = array();
-    $categories = db_query('SELECT c.cid, c.title FROM {aggregator_category} c ORDER BY title');
-    foreach ($categories as $category) {
-      $options[$category->cid] = check_plain($category->title);
-      if (!empty($feed->categories) && in_array($category->cid, array_keys($feed->categories))) {
-        $values[] = $category->cid;
+    $categories = $this->categoryStorageController->loadAllCategories();
+    foreach ($categories as $cid => $title) {
+      $options[$cid] = check_plain($title);
+      if (!empty($feed->categories) && in_array($cid, array_keys($feed->categories))) {
+        $values[] = $cid;
       }
     }
 
@@ -90,13 +129,7 @@ public function form(array $form, array &$form_state) {
   public function validate(array $form, array &$form_state) {
     $feed = $this->buildEntity($form, $form_state);
     // Check for duplicate titles.
-    if ($feed->id()) {
-      $result = db_query("SELECT title, url FROM {aggregator_feed} WHERE (title = :title OR url = :url) AND fid <> :fid", array(':title' => $feed->label(), ':url' => $feed->url->value, ':fid' => $feed->id()));
-    }
-    else {
-      $result = db_query("SELECT title, url FROM {aggregator_feed} WHERE title = :title OR url = :url", array(':title' => $feed->label(), ':url' => $feed->url->value));
-    }
-
+    $result = $this->feedStorage->getFeedDuplicates($feed);
     foreach ($result as $item) {
       if (strcasecmp($item->title, $feed->label()) == 0) {
         form_set_error('title', t('A feed named %feed already exists. Enter a unique title.', array('%feed' => $feed->label())));
diff --git a/core/modules/aggregator/lib/Drupal/aggregator/FeedStorageController.php b/core/modules/aggregator/lib/Drupal/aggregator/FeedStorageController.php
index 7b6be0a..6ced8ba 100644
--- a/core/modules/aggregator/lib/Drupal/aggregator/FeedStorageController.php
+++ b/core/modules/aggregator/lib/Drupal/aggregator/FeedStorageController.php
@@ -8,11 +8,10 @@
 namespace Drupal\aggregator;
 
 use Drupal\Core\Entity\DatabaseStorageControllerNG;
-use Drupal\aggregator\Entity\Feed;
 use Drupal\Core\Entity\EntityInterface;
 
 /**
- * Controller class for aggregators feeds.
+ * Controller class for aggregator's feeds.
  *
  * This extends the Drupal\Core\Entity\DatabaseStorageController class, adding
  * required special handling for feed entities.
@@ -117,7 +116,7 @@ public function loadCategories(array $feeds) {
   /**
    * {@inheritdoc}
    */
-  public function saveCategories(Feed $feed, array $categories) {
+  public function saveCategories(EntityInterface $feed, array $categories) {
     foreach ($categories as $cid => $value) {
       if ($value) {
         $this->database->insert('aggregator_category_feed')
@@ -140,4 +139,18 @@ public function deleteCategories(array $feeds) {
       ->execute();
   }
 
+  /**
+   * {@inheritdoc}
+   */
+  public function getFeedDuplicates(EntityInterface $feed) {
+    if ($feed->id()) {
+      $query = $this->database->query("SELECT title, url FROM {aggregator_feed} WHERE (title = :title OR url = :url) AND fid <> :fid", array(':title' => $feed->label(), ':url' => $feed->url->value, ':fid' => $feed->id()));
+    }
+    else {
+      $query = $this->database->query("SELECT title, url FROM {aggregator_feed} WHERE title = :title OR url = :url", array(':title' => $feed->label(), ':url' => $feed->url->value));
+    }
+
+    return $query;
+  }
+
 }
diff --git a/core/modules/aggregator/lib/Drupal/aggregator/FeedStorageControllerInterface.php b/core/modules/aggregator/lib/Drupal/aggregator/FeedStorageControllerInterface.php
index c991b0f..cd8162c 100644
--- a/core/modules/aggregator/lib/Drupal/aggregator/FeedStorageControllerInterface.php
+++ b/core/modules/aggregator/lib/Drupal/aggregator/FeedStorageControllerInterface.php
@@ -7,7 +7,7 @@
 
 namespace Drupal\aggregator;
 
-use Drupal\aggregator\Entity\Feed;
+use Drupal\Core\Entity\EntityInterface;
 use Drupal\Core\Entity\EntityStorageControllerInterface;
 
 /**
@@ -18,7 +18,7 @@
   /**
    * Loads the categories of a feed.
    *
-   * @param array $entities
+   * @param array $feeds
    *   A list of feed entities keyed by feed id. Each entity will get a
    *   categories property added.
    */
@@ -27,12 +27,12 @@ public function loadCategories(array $feeds);
   /**
    * Saves the categories of a feed.
    *
-   * @param Feed $feed
+   * @param \Drupal\Core\Entity\EntityInterface $feed
    *   The feed entity.
    * @param array $categories
    *   The array of categories.
    */
-  public function saveCategories(Feed $feed, array $categories);
+  public function saveCategories(EntityInterface $feed, array $categories);
 
   /**
    * Deletes the categories of a feed.
@@ -42,4 +42,11 @@ public function saveCategories(Feed $feed, array $categories);
    */
   public function deleteCategories(array $feeds);
 
+  /**
+   * Provides a list of duplicate feeds.
+   *
+   * @param \Drupal\Core\Entity\EntityInterface $feed
+   *   The feed entity.
+   */
+  public function getFeedDuplicates(EntityInterface $feed);
 }
diff --git a/core/modules/aggregator/lib/Drupal/aggregator/Form/OpmlFeedAdd.php b/core/modules/aggregator/lib/Drupal/aggregator/Form/OpmlFeedAdd.php
index 0959fb0..0048bbd 100644
--- a/core/modules/aggregator/lib/Drupal/aggregator/Form/OpmlFeedAdd.php
+++ b/core/modules/aggregator/lib/Drupal/aggregator/Form/OpmlFeedAdd.php
@@ -12,6 +12,7 @@
 use Drupal\Core\Entity\EntityManager;
 use Drupal\Core\Entity\Query\QueryFactory;
 use Drupal\Core\Form\FormInterface;
+use Drupal\aggregator\CategoryStorageControllerInterface;
 use Symfony\Component\DependencyInjection\ContainerInterface;
 use Guzzle\Http\Exception\RequestException;
 use Guzzle\Http\Exception\BadResponseException;
@@ -51,22 +52,32 @@ class OpmlFeedAdd implements ControllerInterface, FormInterface {
   protected $httpClient;
 
   /**
+   * The category storage controller.
+   *
+   * @var \Drupal\aggregator\CategoryStorageControllerInterface
+   */
+  protected $categoryStorageController;
+
+  /**
    * Constructs a database object.
    *
-   * @param \Drupal\Core\Database\Connection; $database
+   * @param \Drupal\Core\Database\Connection $database
    *   The database object.
    * @param \Drupal\Core\Entity\Query\QueryFactory $query_factory
    *   The entity query object.
    * @param \Drupal\Core\Entity\EntityManager $entity_manager
    *   The entity manager.
-   * @param \Guzzle\Http\Client
+   * @param \Guzzle\Http\Client $http_client
    *   The Guzzle HTTP client.
+   * @param \Drupal\aggregator\CategoryStorageControllerInterface $category_storage_controller
+   *   The category storage controller.
    */
-  public function __construct(Connection $database, QueryFactory $query_factory, EntityManager $entity_manager, Client $http_client) {
+  public function __construct(Connection $database, QueryFactory $query_factory, EntityManager $entity_manager, Client $http_client, CategoryStorageControllerInterface $category_storage_controller) {
     $this->database = $database;
     $this->queryFactory = $query_factory;
     $this->entityManager = $entity_manager;
     $this->httpClient = $http_client;
+    $this->categoryStorageController = $category_storage_controller;
   }
 
   /**
@@ -77,7 +88,8 @@ public static function create(ContainerInterface $container) {
       $container->get('database'),
       $container->get('entity.query'),
       $container->get('plugin.manager.entity'),
-      $container->get('http_default_client')
+      $container->get('http_default_client'),
+      $container->get('aggregator.category.storage')
     );
   }
 
@@ -122,7 +134,7 @@ public function buildForm(array $form, array &$form_state) {
     );
 
     // Handling of categories.
-    $options = array_map('check_plain', $this->database->query("SELECT cid, title FROM {aggregator_category} ORDER BY title")->fetchAllKeyed());
+    $options = array_map('check_plain', $this->categoryStorageController->loadAllCategories());
     if ($options) {
       $form['category'] = array(
         '#type' => 'checkboxes',