added Tag entity and mapper

lib/Db/Tag.php

@@ -0,0 +1,28 @@
+<?php
+
+namespace OCA\GroupfolderTags\Db;
+
+use JsonSerializable;
+
+use OCP\AppFramework\Db\Entity;
+
+class Tag extends Entity implements JsonSerializable {
+	protected $groupFolderId;
+	protected $tagKey;
+	protected $tagValue;
+	protected $lastUpdatedTimestamp;
+
+	public function __construct() {
+		$this->addType('groupFolderId','integer');
+		$this->addType('lastUpdatedTimestamp','integer');
+	}
+
+	public function jsonSerialize(): array {
+		return [
+			'groupFolderId' => $this->groupFolderId,
+			'tagKey' => $this->tagKey,
+			'tagValue' => $this->tagValue,
+			'lastUpdatedTimestamp' => $this->lastUpdatedTimestamp,
+		];
+	}
+}

lib/Db/TagMapper.php

@@ -0,0 +1,54 @@
+<?php
+
+namespace OCA\GroupfolderTags\Db;
+
+use OCP\AppFramework\Db\DoesNotExistException;
+use OCP\AppFramework\Db\Entity;
+use OCP\AppFramework\Db\QBMapper;
+use OCP\DB\QueryBuilder\IQueryBuilder;
+use OCP\IDBConnection;
+
+class TagMapper extends QBMapper {
+	public const TABLENAME = 'groupfolder_tags';
+
+	public function __construct(IDBConnection $db) {
+		parent::__construct($db, self::TABLENAME, Tag::class);
+	}
+
+	/**
+	 * @param int $groupFolderId
+	 * @param string $tagKey
+	 * @return Entity|Tag
+	 * @throws \OCP\AppFramework\Db\MultipleObjectsReturnedException
+	 * @throws DoesNotExistException
+	 */
+	public function find(int $groupFolderId, string $tagKey): Tag {
+		/* @var $qb IQueryBuilder */
+		$qb = $this->db->getQueryBuilder();
+		$qb->select('*')
+			->from(self::TABLENAME)
+			->where($qb->expr()->eq('group_folder_id', $qb->createNamedParameter($groupFolderId, IQueryBuilder::PARAM_INT)))
+			->andWhere($qb->expr()->eq('tag_key', $qb->createNamedParameter($tagKey)));
+		
+		return $this->findEntity($qb);
+	}
+
+	/**
+	 * @param string $tagKey
+     * @param string|null $tagValue
+	 * @return array
+	 */
+	public function findAll(string $tagKey, ?string $tagValue): array {
+		/* @var $qb IQueryBuilder */
+		$qb = $this->db->getQueryBuilder();
+		$qb->select('*')
+			->from(self::TABLENAME)
+			->where($qb->expr()->eq('tag_key', $qb->createNamedParameter($tagKey)));
+
+        if(isset($tagValue)) {
+            $qb->andWhere($qb->expr()->eq('tag_value', $qb->createNamedParameter($tagValue)));
+        }
+		
+		return $this->findEntities($qb);
+	}
+}