MINOR: make use of getParent method to make faster

This change will make Silverstripe much faster (i hope), because it uses SiteTree::getParent() instead of the magic / custom method Parent()

code/Model/SiteTree.php

@@ -684,7 +684,7 @@ public function getMimeType()
     public function RelativeLink($action = null)
     {
         if ($this->ParentID && self::config()->get('nested_urls')) {
-            $parent = $this->Parent();
+            $parent = $this->getParent();
             // If page is removed select parent from version history (for archive page view)
             if ((!$parent || !$parent->exists()) && !$this->isOnDraft()) {
                 $parent = Versioned::get_latest_version(self::class, $this->ParentID);
@@ -809,7 +809,7 @@ public function isOrphaned()
         }
 
         // Parent must exist and not be an orphan itself
-        $parent = $this->Parent();
+        $parent = $this->getParent();
         return !$parent || !$parent->exists() || $parent->isOrphaned();
     }
 
@@ -863,7 +863,7 @@ public function InSection($sectionName)
             if ($sectionName === $page->URLSegment) {
                 return true;
             }
-            $page = $page->Parent();
+            $page = $page->getParent();
         }
         return false;
     }
@@ -966,7 +966,7 @@ public function getBreadcrumbItems($maxDepth = 20, $stopAtPageType = false, $sho
                 $pages[] = $page;
             }
 
-            $page = $page->Parent();
+            $page = $page->getParent();
         }
 
         return new ArrayList(array_reverse($pages ?? []));
@@ -995,13 +995,13 @@ public function setParent($item)
     /**
      * Get the parent of this page.
      *
-     * @return SiteTree Parent of this page
+     * @return SiteTree|null
      */
     public function getParent()
     {
         $parentID = $this->getField("ParentID");
         if ($parentID) {
-            return SiteTree::get_by_id(self::class, $parentID);
+            return SiteTree::get_by_id($parentID);
         }
         return null;
     }
@@ -1176,7 +1176,7 @@ public function canView($member = null)
         // check for inherit
         if ($this->CanViewType === InheritedPermissions::INHERIT) {
             if ($this->ParentID) {
-                return $this->Parent()->canView($member);
+                return $this->getParent()->canView($member);
             } else {
                 return $this->getSiteConfig()->canViewPages($member);
             }
@@ -1872,7 +1872,7 @@ public function validURLSegment()
         // Check known urlsegment blacklists
         if (self::config()->get('nested_urls') && $this->ParentID) {
             // Guard against url segments for sub-pages
-            $parent = $this->Parent();
+            $parent = $this->getParent();
             if ($controller = ModelAsController::controller_for($parent)) {
                 if ($controller instanceof Controller && $controller->hasAction($this->URLSegment)) {
                     return false;
@@ -2132,7 +2132,7 @@ public function getCMSFields()
 
         $baseLink = Controller::join_links(
             Director::absoluteBaseURL(),
-            (self::config()->get('nested_urls') && $this->ParentID ? $this->Parent()->RelativeLink(true) : null)
+            (self::config()->get('nested_urls') && $this->ParentID ? $this->getParent()->RelativeLink(true) : null)
         );
 
         $urlsegment = SiteTreeURLSegmentField::create("URLSegment", $this->fieldLabel('URLSegment'))
@@ -2755,7 +2755,7 @@ protected function getClassDropdown()
                 if ($instance instanceof HiddenClass) {
                     continue;
                 }
-                if (!$instance->canCreate(null, ['Parent' => $this->ParentID ? $this->Parent() : null])) {
+                if (!$instance->canCreate(null, ['Parent' => $this->ParentID ? $this->getParent() : null])) {
                     continue;
                 }
             }
@@ -3033,7 +3033,7 @@ public function Level($level)
     {
         $parent = $this;
         $stack = [$parent];
-        while (($parent = $parent->Parent()) && $parent->exists()) {
+        while (($parent = $parent->getParent()) && $parent->exists()) {
             array_unshift($stack, $parent);
         }
 
@@ -3048,7 +3048,7 @@ public function Level($level)
     public function getPageLevel()
     {
         if ($this->ParentID) {
-            return 1 + $this->Parent()->getPageLevel();
+            return 1 + $this->getParent()->getPageLevel();
         }
         return 1;
     }