diff --git a/core/modules/aggregator/lib/Drupal/aggregator/CategoryStorageController.php b/core/modules/aggregator/lib/Drupal/aggregator/CategoryStorageController.php
index 0922531..e13ea8d 100644
--- a/core/modules/aggregator/lib/Drupal/aggregator/CategoryStorageController.php
+++ b/core/modules/aggregator/lib/Drupal/aggregator/CategoryStorageController.php
@@ -125,4 +125,11 @@ public function updateItem($iid, array $cids) {
     }
   }
 
+  /**
+   * {@inheritdoc}
+   */
+  public function loadAllKeyed() {
+    return $this->database->query('SELECT c.cid, c.title FROM {aggregator_category} c ORDER BY title')->fetchAllKeyed();
+  }
+
 }
diff --git a/core/modules/aggregator/lib/Drupal/aggregator/CategoryStorageControllerInterface.php b/core/modules/aggregator/lib/Drupal/aggregator/CategoryStorageControllerInterface.php
index 0494415..63393bd 100644
--- a/core/modules/aggregator/lib/Drupal/aggregator/CategoryStorageControllerInterface.php
+++ b/core/modules/aggregator/lib/Drupal/aggregator/CategoryStorageControllerInterface.php
@@ -87,5 +87,13 @@ public function loadByItem($item_id);
    */
   public function updateItem($iid, array $cids);
 
+  /**
+   * Loads all categories.
+   *
+   * @return array
+   *   An array keyed on cid listing all available categories.
+   */
+  public function loadAllKeyed();
+
 }
 
diff --git a/core/modules/aggregator/lib/Drupal/aggregator/FeedFormController.php b/core/modules/aggregator/lib/Drupal/aggregator/FeedFormController.php
index d640880..0ca5bef 100644
--- a/core/modules/aggregator/lib/Drupal/aggregator/FeedFormController.php
+++ b/core/modules/aggregator/lib/Drupal/aggregator/FeedFormController.php
@@ -9,7 +9,10 @@
 
 use Drupal\Component\Utility\String;
 use Drupal\Core\Entity\ContentEntityFormController;
+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.
@@ -17,6 +20,43 @@
 class FeedFormController extends ContentEntityFormController {
 
   /**
+   * The feed storage.
+   *
+   * @var \Drupal\Core\Entity\EntityStorageControllerInterface
+   */
+  protected $feedStorageController;
+
+  /**
+   * 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->feedStorageController = $feed_storage;
+    $this->categoryStorageController = $category_storage_controller;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function create(ContainerInterface $container) {
+    return new static(
+      $container->get('plugin.manager.entity')->getStorageController('aggregator_feed'),
+      $container->get('aggregator.category.storage')
+    );
+  }
+
+  /**
    * {@inheritdoc}
    */
   public function form(array $form, array &$form_state) {
@@ -58,11 +98,11 @@ 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] = String::checkPlain($category->title);
-      if (!empty($feed->categories) && in_array($category->cid, array_keys($feed->categories))) {
-        $values[] = $category->cid;
+    $categories = $this->categoryStorageController->loadAllKeyed();
+    foreach ($categories as $cid => $title) {
+      $options[$cid] = String::checkPlain($title);
+      if (!empty($feed->categories) && in_array($cid, array_keys($feed->categories))) {
+        $values[] = $cid;
       }
     }
 
@@ -85,13 +125,7 @@ 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 = $this->feedStorageController->getFeedDuplicates($feed);
     foreach ($result as $item) {
       if (strcasecmp($item->title, $feed->label()) == 0) {
         form_set_error('title', $this->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 17ea1e2..8f8fd71 100644
--- a/core/modules/aggregator/lib/Drupal/aggregator/FeedStorageController.php
+++ b/core/modules/aggregator/lib/Drupal/aggregator/FeedStorageController.php
@@ -7,12 +7,11 @@
 
 namespace Drupal\aggregator;
 
+use Drupal\aggregator\FeedInterface;
 use Drupal\Core\Entity\FieldableDatabaseStorageController;
-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.
@@ -39,7 +38,7 @@ public function loadCategories(array $feeds) {
   /**
    * {@inheritdoc}
    */
-  public function saveCategories(Feed $feed, array $categories) {
+  public function saveCategories(FeedInterface $feed, array $categories) {
     foreach ($categories as $cid => $value) {
       if ($value) {
         $this->database->insert('aggregator_category_feed')
@@ -62,4 +61,18 @@ public function deleteCategories(array $feeds) {
       ->execute();
   }
 
+  /**
+   * {@inheritdoc}
+   */
+  public function getFeedDuplicates(FeedInterface $feed) {
+    if ($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->fetchAll();
+  }
+
 }
diff --git a/core/modules/aggregator/lib/Drupal/aggregator/FeedStorageControllerInterface.php b/core/modules/aggregator/lib/Drupal/aggregator/FeedStorageControllerInterface.php
index c991b0f..ab33938 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\aggregator\FeedInterface;
 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\aggregator\Entity\FeedInterface $feed
    *   The feed entity.
    * @param array $categories
    *   The array of categories.
    */
-  public function saveCategories(Feed $feed, array $categories);
+  public function saveCategories(FeedInterface $feed, array $categories);
 
   /**
    * Deletes the categories of a feed.
@@ -42,4 +42,15 @@ public function saveCategories(Feed $feed, array $categories);
    */
   public function deleteCategories(array $feeds);
 
+  /**
+   * Provides a list of duplicate feeds.
+   *
+   * @param \Drupal\aggregator\Entity\FeedInterface $feed
+   *   The feed entity.
+   *
+   * @return
+   *   An array with the list of duplicated feeds.
+   */
+  public function getFeedDuplicates(FeedInterface $feed);
+
 }
diff --git a/core/modules/aggregator/lib/Drupal/aggregator/Form/OpmlFeedAdd.php b/core/modules/aggregator/lib/Drupal/aggregator/Form/OpmlFeedAdd.php
index 5727cf6..abf1cad 100644
--- a/core/modules/aggregator/lib/Drupal/aggregator/Form/OpmlFeedAdd.php
+++ b/core/modules/aggregator/lib/Drupal/aggregator/Form/OpmlFeedAdd.php
@@ -7,15 +7,15 @@
 
 namespace Drupal\aggregator\Form;
 
+use Drupal\aggregator\CategoryStorageControllerInterface;
 use Drupal\aggregator\FeedStorageControllerInterface;
 use Drupal\Component\Utility\Url;
-use Drupal\Core\Database\Connection;
 use Drupal\Core\Entity\Query\QueryFactory;
 use Drupal\Core\Form\FormBase;
 use Symfony\Component\DependencyInjection\ContainerInterface;
 use Guzzle\Http\Exception\RequestException;
 use Guzzle\Http\Exception\BadResponseException;
-use Guzzle\Http\Client;
+use Guzzle\Http\ClientInterface;
 
 /**
  * Imports feeds from OPML.
@@ -23,13 +23,6 @@
 class OpmlFeedAdd extends FormBase {
 
   /**
-   * The database connection object.
-   *
-   * @var \Drupal\Core\Database\Connection
-   */
-  protected $database;
-
-  /**
    * The entity query factory object.
    *
    * @var \Drupal\Core\Entity\Query\QueryFactory
@@ -41,32 +34,39 @@ class OpmlFeedAdd extends FormBase {
    *
    * @var \Drupal\aggregator\FeedStorageControllerInterface
    */
-  protected $feedStorage;
+  protected $feedStorageController;
 
   /**
    * The HTTP client to fetch the feed data with.
    *
-   * @var \Guzzle\Http\Client
+   * @var \Guzzle\Http\ClientInterface
    */
   protected $httpClient;
 
   /**
+   * The category storage controller.
+   *
+   * @var \Drupal\aggregator\CategoryStorageControllerInterface
+   */
+  protected $categoryStorageController;
+
+  /**
    * Constructs a database object.
    *
-   * @param \Drupal\Core\Database\Connection $database
-   *   The database object.
    * @param \Drupal\Core\Entity\Query\QueryFactory $query_factory
    *   The entity query object.
    * @param \Drupal\aggregator\FeedStorageControllerInterface $feed_storage
    *   The feed storage.
-   * @param \Guzzle\Http\Client $http_client
+   * @param \Guzzle\Http\ClientInterface $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, FeedStorageControllerInterface $feed_storage, Client $http_client) {
-    $this->database = $database;
+  public function __construct(QueryFactory $query_factory, FeedStorageControllerInterface $feed_storage, ClientInterface $http_client, CategoryStorageControllerInterface $category_storage_controller) {
     $this->queryFactory = $query_factory;
-    $this->feedStorage = $feed_storage;
+    $this->feedStorageController = $feed_storage;
     $this->httpClient = $http_client;
+    $this->categoryStorageController = $category_storage_controller;
   }
 
   /**
@@ -74,10 +74,10 @@ public function __construct(Connection $database, QueryFactory $query_factory, F
    */
   public static function create(ContainerInterface $container) {
     return new static(
-      $container->get('database'),
       $container->get('entity.query'),
       $container->get('entity.manager')->getStorageController('aggregator_feed'),
-      $container->get('http_default_client')
+      $container->get('http_default_client'),
+      $container->get('aggregator.category.storage')
     );
   }
 
@@ -115,7 +115,7 @@ 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', $this->categoryStorageController->loadAllKeyed());
     if ($options) {
       $form['category'] = array(
         '#type' => 'checkboxes',
@@ -192,7 +192,7 @@ public function submitForm(array &$form, array &$form_state) {
       $ids = $query
         ->condition($condition)
         ->execute();
-      $result = $this->feedStorage->loadMultiple($ids);
+      $result = $this->feedStorageController->loadMultiple($ids);
       foreach ($result as $old) {
         if (strcasecmp($old->label(), $feed['title']) == 0) {
           drupal_set_message($this->t('A feed named %title already exists.', array('%title' => $old->label())), 'warning');
@@ -204,7 +204,7 @@ public function submitForm(array &$form, array &$form_state) {
         }
       }
 
-      $new_feed = $this->feedStorage->create(array(
+      $new_feed = $this->feedStorageController->create(array(
         'title' => $feed['title'],
         'url' => $feed['url'],
         'refresh' => $form_state['values']['refresh'],