Add category system to categorize posts (readme)

This commit implements a new category system to categorize posts. Each
category can have an unlimited number of nested children categories. A
single post don't necessarily need to be in a category, but it can.

Each category can have a full content body like posts or pages, so you
have enough space to describe the content of your categories.

Please note that you need to have at least the following MySQL/MariaDB
versions to use the category system, because it uses "WITH RECURSIVE"
database queries, the so-called "Common-Table-Expressions (CTE)".

MariaDB: 10.2.2
MySQL: 8.0

See: https://mariadb.com/kb/en/with/
See: https://dev.mysql.com/doc/refman/8.0/en/with.html

1 files changed, 12 insertions, 0 deletions

diff --git a/core/namespace/ORM/Repositories/Post.php b/core/namespace/ORM/Repositories/Post.php
index 8eac12f..d6328e6 100644
--- a/core/namespace/ORM/Repositories/Post.php
+++ b/core/namespace/ORM/Repositories/Post.php
@@ -2,6 +2,7 @@
 namespace ORM\Repositories;
 use ORM\Repository;
 use ORM\Entities\User;
+use ORM\Entities\Category;
 
 class Post extends Repository {
 	public static function getTableName(): string { return 'post'; }
@@ -16,4 +17,15 @@ class Post extends Repository {
 
 		return $Statement->fetchColumn();
 	}
+
+	# TODO: This only gets the count of the direct category, not its children
+	public function getCountByCategory(Category $Category): int {
+		$query = 'SELECT COUNT(id) FROM %s WHERE category = ?';
+		$query = sprintf($query, static::getTableName());
+
+		$Statement = $this->Database->prepare($query);
+		$Statement->execute([$Category->getID()]);
+
+		return $Statement->fetchColumn();
+	}
 }