diff --git a/oowp.php b/oowp.php
index daa8ca0..6f55026 100644
--- a/oowp.php
+++ b/oowp.php
@@ -3,7 +3,7 @@
 Plugin Name: Object-oriented WordPress (OOWP)
 Plugin URI: https://github.com/outlandishideas/oowp
 Description: OOWP is a tool for WordPress theme developers that makes templating in WordPress more sensible. It replaces [The Loop](https://codex.wordpress.org/The_Loop) and contextless functions such as the_title() with object-oriented methods such as $event->title(), $event->parent() and $event->getConnected('people').
-Version: 0.9
+Version: 3.0.3
 */
 
 use Outlandish\Wordpress\Oowp\Shortcodes\ListPostsShortcode;
diff --git a/src/OowpQuery.php b/src/OowpQuery.php
index a7d4ffd..ae554db 100644
--- a/src/OowpQuery.php
+++ b/src/OowpQuery.php
@@ -17,19 +17,18 @@ class OowpQuery extends \WP_Query implements \IteratorAggregate, \ArrayAccess, \
      */
     function __construct($query = '')
     {
-        global $wp_post_types;
-
-        $defaults = array(
+        $defaults = [
             'posts_per_page' => -1,
             'post_status' => 'publish'
-        );
+        ];
         $query    = wp_parse_args($query, $defaults);
 
         // If there is no post type, or the post type is singular and isn't valid, replace it with any *except*
         // 'attachment' which can cause crashes on ?preview=true if a file title matches a render-able post's.
-        if (!isset($query['post_type']) || (!is_array($query['post_type']) && !array_key_exists($query['post_type'],
-                    $wp_post_types))) {
-            $query['post_type'] = array_values(array_diff(get_post_types(), array('attachment')));
+        $validPostTypes    = get_post_types();
+        $requestedPostType = $query['post_type'] ?? 'any';
+        if (is_scalar($requestedPostType) && !array_key_exists($requestedPostType, $validPostTypes)) {
+            $query['post_type'] = array_values(array_diff($validPostTypes, ['attachment']));
         }
 
         parent::__construct($query);
@@ -115,12 +114,20 @@ public function sortByIds($ids)
 
     /**
      * Convert WP_Post objects to WordpressPost
-     * @return WordpressPost[]
+     * If $query['fields'] is 'ids', then this will just return the post IDs
+     * If $query['fields'] is 'id->parent', then this will return an array of objects that represents the parent-child relationships
+     * See https://developer.wordpress.org/reference/classes/wp_query/#return-fields-parameter
+     * @return WordpressPost[]|int[]|\stdClass[]
      */
     public function &get_posts()
     {
         parent::get_posts();
 
+        $fields = $this->query['fields'] ?? 'all';
+        if ($fields && $fields !== 'all') {
+            return $this->posts;
+        }
+
         foreach ($this->posts as $i => $post) {
             $this->posts[$i] = WordpressPost::createWordpressPost($post);
         }
diff --git a/src/PostTypes/WordpressPost.php b/src/PostTypes/WordpressPost.php
index 305a34e..66d0309 100644
--- a/src/PostTypes/WordpressPost.php
+++ b/src/PostTypes/WordpressPost.php
@@ -43,7 +43,6 @@
  */
 abstract class WordpressPost
 {
-
     protected $_cache = array();
     protected static $_staticCache = array();
 
@@ -499,16 +498,12 @@ public function parent()
     {
         $parentId = $this->post_parent;
         if (!$parentId) {
-            $parentId = static::postTypeParentId();
-        }
-        $parentSlug = static::postTypeParentSlug();
-        if (empty($parentId) && empty($parentSlug)) {
-            return null;
+            return static::postTypeParent();
         }
 
         $parent = $this->getCacheValue();
         if (!$parent) {
-            $parent = $parentId ? WordpressPost::fetchById($parentId) : WordpressPost::fetchBySlug($parentSlug);
+            $parent = WordpressPost::fetchById($parentId);
             $this->setCacheValue($parent);
         }
         return $parent;
@@ -536,6 +531,28 @@ public static function postTypeParentSlug()
         return '';
     }
 
+    /**
+     * Gets the parent for posts of this type, based on either the ID or slug, whichever is defined for the post type
+     * @return WordpressPost|null
+     */
+    public static function postTypeParent()
+    {
+        $key = 'post_type_parent__' . static::postType();
+        if (!array_key_exists($key, WordpressPost::$_staticCache)) {
+            $parentId   = static::postTypeParentId();
+            $parentSlug = static::postTypeParentSlug();
+            if ($parentId) {
+                $parent = WordpressPost::fetchById($parentId);
+            } elseif ($parentSlug) {
+                $parent = WordpressPost::fetchBySlug($parentSlug);
+            } else {
+                $parent = null;
+            }
+            WordpressPost::$_staticCache[$key] = $parent;
+        }
+        return WordpressPost::$_staticCache[$key];
+    }
+
     /**
      * Traverses up the getParent() hierarchy until finding one with no parent, which is returned
      */
@@ -1022,8 +1039,8 @@ static function getQueriedObject()
      */
     static function registerConnection($targetPostType, $parameters = array(), $connectionName = null)
     {
-        return PostTypeManager::get()->registerConnection(self::postType(), $targetPostType, $parameters,
-            $connectionName);
+        return PostTypeManager::get()
+            ->registerConnection(self::postType(), $targetPostType, $parameters, $connectionName);
     }
 
     /**
@@ -1100,6 +1117,20 @@ public static function fetchAll($queryArgs = array())
         return $query;
     }
 
+    /**
+     * @static
+     * Does the same querying as in fetchAll, but only returns the IDs of the matches posts
+     *
+     * @param array $queryArgs Accepts a wp_query $queryArgs array which overwrites the defaults
+     * @return int[]
+     */
+    public static function fetchIds($queryArgs = [])
+    {
+        $queryArgs['fields'] = 'ids';
+        $query               = static::fetchAll($queryArgs);
+        return $query->posts;
+    }
+
     /**
      * @deprecated
      */