Aggregator feeds and feed items have been converted to entities

Feeds

Aggregator feeds and feed items are now Content Entities.

Whenever a feed/feed item id needs to be retrieved use $feed->id() and $feed->label() for title.

D7

// Feeds.
$feeds = db_query('SELECT * FROM {aggregator_feed}');
foreach ($feeds as $feed) {
  $options[$feed->fid] = $feed->title;
}
// Feed items.
$items = db_query('SELECT * FROM {aggregator_item}');
foreach ($items as $item) {
  $options[$item->iid] = $item->title;
}

D8

// Feeds.
use Drupal\aggregator\Entity\Feed;
$feeds = Feed::loadMultiple();
foreach ($feeds as $feed) {
  $options[$feed->id()] = $feed->label();
}
// Feed items.
use Drupal\aggregator\Entity\Item;
$feeds = Item::loadMultiple();
foreach ($items as $item) {
  $options[$item->id()] = $item->label();
}

- aggregator_save_feed() and aggregator_save_item() have been removed in favor of save() method

D7

// Feeds.
$feed = array(
  'title' => $title,
  'url' => $feed_url,
  'refresh' => '900',
  'block' => 5,
);
aggregator_save_feed($feed);

// Feed items.
$item = array(
  'fid' => $fid, 
  'timestamp' => $timestamp, 
  'title' => $title, 
  'link' => $link, 
  'author' => $author, 
  'description' => $description, 
  'guid' => $guid,
);
aggregator_save_item($item);

D8

// Feeds.
$feed = Feed::create(array(
  'title' => $title,
  'url' => $feed_url,
  'refresh' => 900,
  'block' => 5,
));
$feed->save();

// Feed items.
$item = Item::create(array(
  'fid' => $fid, 
  'timestamp' => $timestamp, 
  'title' => $title, 
  'link' => $link, 
  'author' => $author, 
  'description' => $description, 
  'guid' => $guid,
));
$item->save();

- aggregator_feed_source theming function renamed to aggregator_feed
D7

function THEME_preprocess_aggregator_feed_source(&$variables) {
  $feed = $variables['aggregator_feed'];
  // Do stuff
}

D8

function THEME_preprocess_aggregator_feed(&$variables) {
  // Notice the extra 'elements' key.
  $feed = $variables['elements']['#aggregator_feed'];
  // Do stuff
}

- aggregator_summary_item and aggregator_summary_items has been removed. aggregator_item can now be used, with a check for the view mode:
D7

function THEME_preprocess_aggregator_summary_item(&$variables) {
  $item = $variables['aggregator_item'];
  // Do stuff
}
function THEME_preprocess_aggregator_summary_items(&$variables) {
  $item = $variables['aggregator_item'];
  // Do stuff
}

D8

function THEME_preprocess_aggregator_item(&$variables) {
  // Notice the extra 'elements' key.
  $item = $variables['elements']['#aggregator_item'];
  if ($variables['elements']['#view_mode'] == 'summary') {
    // Do stuff
  }
}