silverstripe blog suggested posts

suggested.php

BlogPost::get()
  ->filter(['ParentID' => $this->owner->ParentID])
  ->leftJoin('BlogPost_Categories', 'BlogPost.ID = BlogPost_Categories.BlogPostID')
  ->where(
  'BlogCategoryID IN (
    SELECT BlogCategoryID FROM "BlogPost"
    LEFT JOIN BlogPost_Categories ON BlogPost.ID = BlogPost_Categories.BlogPostID
    WHERE BlogPost.ID = ' . $this->owner->ID . ')')
  ->exclude(['ID' => $this->owner->ID])
  ->sort('RAND()')
  ->limit($length);