Add systemtag_group table and get/set methods

Added systemtag to group mapping table.
Added methods in ISystemTagManager to get/set the group mappings.

db_structure.xml

@@ -1380,6 +1380,49 @@
 
 	</table>
 
+	<table>
+
+		<!--
+		System tag to group mapping
+		-->
+		<name>*dbprefix*systemtag_group</name>
+
+		<declaration>
+
+		<!-- Foreign Key systemtag::id -->
+		<field>
+			<name>systemtagid</name>
+			<type>integer</type>
+			<default>0</default>
+			<notnull>true</notnull>
+			<unsigned>true</unsigned>
+			<length>4</length>
+		</field>
+
+		<field>
+			<name>gid</name>
+			<type>string</type>
+			<notnull>true</notnull>
+		</field>
+
+		<index>
+			<name>systemtag_group</name>
+			<primary>true</primary>
+			<unique>true</unique>
+			<field>
+				<name>gid</name>
+				<sorting>ascending</sorting>
+			</field>
+			<field>
+				<name>systemtagid</name>
+				<sorting>ascending</sorting>
+			</field>
+		</index>
+
+		</declaration>
+
+	</table>
+
 	<table>
 
 		<!--

lib/private/SystemTag/SystemTagManager.php

@@ -42,6 +42,7 @@ use OCP\IUser;
 class SystemTagManager implements ISystemTagManager {
 
 	const TAG_TABLE = 'systemtag';
+	const TAG_GROUP_TABLE = 'systemtag_group';
 
 	/** @var IDBConnection */
 	protected $connection;
@@ -365,4 +366,58 @@ class SystemTagManager implements ISystemTagManager {
 	private function createSystemTagFromRow($row) {
 		return new SystemTag((int)$row['id'], $row['name'], (bool)$row['visibility'], (bool)$row['editable']);
 	}
+
+	/**
+	 * {@inheritdoc}
+	 */
+	public function setTagGroups(ISystemTag $tag, $groupIds) {
+		// delete relationships first
+		$this->connection->beginTransaction();
+		try {
+			$query = $this->connection->getQueryBuilder();
+			$query->delete(self::TAG_GROUP_TABLE)
+				->where($query->expr()->eq('systemtagid', $query->createNamedParameter($tag->getId())))
+				->execute();
+
+			// add each group id
+			$query = $this->connection->getQueryBuilder();
+			$query->insert(self::TAG_GROUP_TABLE)
+				->values([
+					'systemtagid' => $query->createNamedParameter($tag->getId()),
+					'gid' => $query->createParameter('gid'),
+				]);
+			foreach ($groupIds as $groupId) {
+				$query->setParameter('gid', $groupId);
+				$query->execute();
+			}
+
+			$this->connection->commit();
+		} catch (\Exception $e) {
+			$this->connection->rollback();
+			throw $e;
+		}
+
+		return false;
+	}
+
+	/**
+	 * {@inheritdoc}
+	 */
+	public function getTagGroups(ISystemTag $tag) {
+		$groupIds = [];
+		$query = $this->connection->getQueryBuilder();
+		$query->select('*')
+			->from(self::TAG_GROUP_TABLE)
+			->where($query->expr()->eq('systemtagid', $query->createNamedParameter($tag->getId())))
+			->orderBy('gid');
+
+		$result = $query->execute();
+		while ($row = $result->fetch()) {
+			$groupIds[] = $row['gid'];
+		}
+
+		$result->closeCursor();
+
+		return $groupIds;
+	}
 }

lib/public/SystemTag/ISystemTagManager.php

@@ -141,4 +141,24 @@ interface ISystemTagManager {
 	 */
 	public function canUserSeeTag(ISystemTag $tag, IUser $userId);
 
+	/**
+	 * Set groups that can assign a given tag.
+	 *
+	 * @param ISystemTag $tag tag for group assignment
+	 * @param string[] $groupIds group ids of groups that can assign/unassign the tag
+	 *
+	 * @since 9.1.0
+	 */
+	public function setTagGroups(ISystemTag $tag, $groupIds);
+
+	/**
+	 * Get groups that can assign a given tag.
+	 *
+	 * @param ISystemTag $tag tag for group assignment
+	 *
+	 * @return string[] group ids of groups that can assign/unassign the tag
+	 *
+	 * @since 9.1.0
+	 */
+	public function getTagGroups(ISystemTag $tag);
 }

tests/lib/SystemTag/SystemTagManagerTest.php

@@ -478,6 +478,23 @@ class SystemTagManagerTest extends TestCase {
 		$this->assertEquals($expectedResult, $this->tagManager->canUserAssignTag($tag1, $user));
 	}
 
+	public function testTagGroups() {
+		$tag1 = $this->tagManager->createTag('tag1', true, false);
+		$tag2 = $this->tagManager->createTag('tag2', true, false);
+		$this->tagManager->setTagGroups($tag1, ['group1', 'group2']);
+		$this->tagManager->setTagGroups($tag2, ['group2', 'group3']);
+
+		$this->assertEquals(['group1', 'group2'], $this->tagManager->getTagGroups($tag1));
+		$this->assertEquals(['group2', 'group3'], $this->tagManager->getTagGroups($tag2));
+
+		// change groups
+		$this->tagManager->setTagGroups($tag1, ['group3', 'group4']);
+		$this->tagManager->setTagGroups($tag2, []);
+
+		$this->assertEquals(['group3', 'group4'], $this->tagManager->getTagGroups($tag1));
+		$this->assertEquals([], $this->tagManager->getTagGroups($tag2));
+	}
+
 	/**
 	 * @param ISystemTag $tag1
 	 * @param ISystemTag $tag2