Merge pull request #20775 from owncloud/comments-manager

add icommentsmanger and icomment implementation

5 files changed, 945 insertions, 0 deletions

diff --git a/lib/private/comments/comment.php b/lib/private/comments/comment.php
new file mode 100644
index 00000000000..219e7ec8e4b
--- /dev/null
+++ b/lib/private/comments/comment.php
@@ -0,0 +1,357 @@
+<?php
+
+namespace OC\Comments;
+
+use OCP\Comments\IComment;
+use OCP\Comments\IllegalIDChangeException;
+
+class Comment implements IComment {
+
+	protected $data = [
+		'id'              => '',
+		'parentId'        => '0',
+		'topmostParentId' => '0',
+		'childrenCount'   => '0',
+		'message'         => '',
+		'verb'            => '',
+		'actorType'       => '',
+		'actorId'         => '',
+		'objectType'      => '',
+		'objectId'        => '',
+		'creationDT'      => null,
+		'latestChildDT'   => null,
+	];
+
+	/**
+	 * Comment constructor.
+	 *
+	 * @param [] $data	optional, array with keys according to column names from
+	 * 					the comments database scheme
+	 */
+	public function __construct(array $data = null) {
+		if(is_array($data)) {
+			$this->fromArray($data);
+		}
+	}
+
+	/**
+	 * returns the ID of the comment
+	 *
+	 * It may return an empty string, if the comment was not stored.
+	 * It is expected that the concrete Comment implementation gives an ID
+	 * by itself (e.g. after saving).
+	 *
+	 * @return string
+	 * @since 9.0.0
+	 */
+	public function getId() {
+		return $this->data['id'];
+	}
+
+	/**
+	 * sets the ID of the comment and returns itself
+	 *
+	 * It is only allowed to set the ID only, if the current id is an empty
+	 * string (which means it is not stored in a database, storage or whatever
+	 * the concrete implementation does), or vice versa. Changing a given ID is
+	 * not permitted and must result in an IllegalIDChangeException.
+	 *
+	 * @param string $id
+	 * @return IComment
+	 * @throws IllegalIDChangeException
+	 * @since 9.0.0
+	 */
+	public function setId($id) {
+		if(!is_string($id)) {
+			throw new \InvalidArgumentException('String expected.');
+		}
+
+		$id = trim($id);
+		if($this->data['id'] === '' || ($this->data['id'] !== '' && $id === '')) {
+			$this->data['id'] = $id;
+			return $this;
+		}
+
+		throw new IllegalIDChangeException('Not allowed to assign a new ID to an already saved comment.');
+	}
+
+	/**
+	 * returns the parent ID of the comment
+	 *
+	 * @return string
+	 * @since 9.0.0
+	 */
+	public function getParentId() {
+		return $this->data['parentId'];
+	}
+
+	/**
+	 * sets the parent ID and returns itself
+	 *
+	 * @param string $parentId
+	 * @return IComment
+	 * @since 9.0.0
+	 */
+	public function setParentId($parentId) {
+		if(!is_string($parentId)) {
+			throw new \InvalidArgumentException('String expected.');
+		}
+		$this->data['parentId'] = trim($parentId);
+		return $this;
+	}
+
+	/**
+	 * returns the topmost parent ID of the comment
+	 *
+	 * @return string
+	 * @since 9.0.0
+	 */
+	public function getTopmostParentId() {
+		return $this->data['topmostParentId'];
+	}
+
+
+	/**
+	 * sets the topmost parent ID and returns itself
+	 *
+	 * @param string $id
+	 * @return IComment
+	 * @since 9.0.0
+	 */
+	public function setTopmostParentId($id) {
+		if(!is_string($id)) {
+			throw new \InvalidArgumentException('String expected.');
+		}
+		$this->data['topmostParentId'] = trim($id);
+		return $this;
+	}
+
+	/**
+	 * returns the number of children
+	 *
+	 * @return int
+	 * @since 9.0.0
+	 */
+	public function getChildrenCount() {
+		return $this->data['childrenCount'];
+	}
+
+	/**
+	 * sets the number of children
+	 *
+	 * @param int $count
+	 * @return IComment
+	 * @since 9.0.0
+	 */
+	public function setChildrenCount($count) {
+		if(!is_int($count)) {
+			throw new \InvalidArgumentException('Integer expected.');
+		}
+		$this->data['childrenCount'] = $count;
+		return $this;
+	}
+
+	/**
+	 * returns the message of the comment
+	 *
+	 * @return string
+	 * @since 9.0.0
+	 */
+	public function getMessage() {
+		return $this->data['message'];
+	}
+
+	/**
+	 * sets the message of the comment and returns itself
+	 *
+	 * @param string $message
+	 * @return IComment
+	 * @since 9.0.0
+	 */
+	public function setMessage($message) {
+		if(!is_string($message)) {
+			throw new \InvalidArgumentException('String expected.');
+		}
+		$this->data['message'] = trim($message);
+		return $this;
+	}
+
+	/**
+	 * returns the verb of the comment
+	 *
+	 * @return string
+	 * @since 9.0.0
+	 */
+	public function getVerb() {
+		return $this->data['verb'];
+	}
+
+	/**
+	 * sets the verb of the comment, e.g. 'comment' or 'like'
+	 *
+	 * @param string $verb
+	 * @return IComment
+	 * @since 9.0.0
+	 */
+	public function setVerb($verb) {
+		if(!is_string($verb) || !trim($verb)) {
+			throw new \InvalidArgumentException('Non-empty String expected.');
+		}
+		$this->data['verb'] = trim($verb);
+		return $this;
+	}
+
+	/**
+	 * returns the actor type
+	 *
+	 * @return string
+	 * @since 9.0.0
+	 */
+	public function getActorType() {
+		return $this->data['actorType'];
+	}
+
+	/**
+	 * returns the actor ID
+	 *
+	 * @return string
+	 * @since 9.0.0
+	 */
+	public function getActorId() {
+		return $this->data['actorId'];
+	}
+
+	/**
+	 * sets (overwrites) the actor type and id
+	 *
+	 * @param string $actorType e.g. 'user'
+	 * @param string $actorId e.g. 'zombie234'
+	 * @return IComment
+	 * @since 9.0.0
+	 */
+	public function setActor($actorType, $actorId) {
+		if(
+		       !is_string($actorType) || !trim($actorType)
+		    || !is_string($actorId)   || !trim($actorId)
+		) {
+			throw new \InvalidArgumentException('String expected.');
+		}
+		$this->data['actorType'] = trim($actorType);
+		$this->data['actorId']   = trim($actorId);
+		return $this;
+	}
+
+	/**
+	 * returns the creation date of the comment.
+	 *
+	 * If not explicitly set, it shall default to the time of initialization.
+	 *
+	 * @return \DateTime
+	 * @since 9.0.0
+	 */
+	public function getCreationDateTime() {
+		return $this->data['creationDT'];
+	}
+
+	/**
+	 * sets the creation date of the comment and returns itself
+	 *
+	 * @param \DateTime $timestamp
+	 * @return IComment
+	 * @since 9.0.0
+	 */
+	public function setCreationDateTime(\DateTime $timestamp) {
+		$this->data['creationDT'] = $timestamp;
+		return $this;
+	}
+
+	/**
+	 * returns the timestamp of the most recent child
+	 *
+	 * @return int
+	 * @since 9.0.0
+	 */
+	public function getLatestChildDateTime() {
+		return $this->data['latestChildDT'];
+	}
+
+	/**
+	 * sets the date of the most recent child
+	 *
+	 * @param \DateTime $dateTime
+	 * @return IComment
+	 * @since 9.0.0
+	 */
+	public function setLatestChildDateTime(\DateTime $dateTime = null) {
+		$this->data['latestChildDT'] = $dateTime;
+		return $this;
+	}
+
+	/**
+	 * returns the object type the comment is attached to
+	 *
+	 * @return string
+	 * @since 9.0.0
+	 */
+	public function getObjectType() {
+		return $this->data['objectType'];
+	}
+
+	/**
+	 * returns the object id the comment is attached to
+	 *
+	 * @return string
+	 * @since 9.0.0
+	 */
+	public function getObjectId() {
+		return $this->data['objectId'];
+	}
+
+	/**
+	 * sets (overwrites) the object of the comment
+	 *
+	 * @param string $objectType e.g. 'file'
+	 * @param string $objectId e.g. '16435'
+	 * @return IComment
+	 * @since 9.0.0
+	 */
+	public function setObject($objectType, $objectId) {
+		if(
+		       !is_string($objectType) || !trim($objectType)
+		    || !is_string($objectId)   || !trim($objectId)
+		) {
+			throw new \InvalidArgumentException('String expected.');
+		}
+		$this->data['objectType'] = trim($objectType);
+		$this->data['objectId']   = trim($objectId);
+		return $this;
+	}
+
+	/**
+	 * sets the comment data based on an array with keys as taken from the
+	 * database.
+	 *
+	 * @param [] $data
+	 * @return IComment
+	 */
+	protected function fromArray($data) {
+		foreach(array_keys($data) as $key) {
+			// translate DB keys to internal setter names
+			$setter = 'set' . str_replace('_', '', ucwords($key,'_'));
+			$setter = str_replace('Timestamp', 'DateTime', $setter);
+
+			if(method_exists($this, $setter)) {
+				$this->$setter($data[$key]);
+			}
+		}
+
+		foreach(['actor', 'object'] as $role) {
+			if(isset($data[$role . '_type']) && isset($data[$role . '_id'])) {
+				$setter = 'set' . ucfirst($role);
+				$this->$setter($data[$role . '_type'], $data[$role . '_id']);
+			}
+		}
+
+		return $this;
+	}
+}
diff --git a/lib/private/comments/manager.php b/lib/private/comments/manager.php
new file mode 100644
index 00000000000..09e59f28370
--- /dev/null
+++ b/lib/private/comments/manager.php
@@ -0,0 +1,549 @@
+<?php
+
+namespace OC\Comments;
+
+use Doctrine\DBAL\Exception\DriverException;
+use OCP\Comments\IComment;
+use OCP\Comments\ICommentsManager;
+use OCP\Comments\NotFoundException;
+use OCP\IDBConnection;
+use OCP\ILogger;
+
+class Manager implements ICommentsManager {
+
+	/** @var  IDBConnection */
+	protected $dbConn;
+
+	/** @var  ILogger */
+	protected $logger;
+
+	/** @var IComment[]  */
+	protected $commentsCache = [];
+
+	public function __construct(
+		IDBConnection $dbConn,
+		ILogger $logger
+	) {
+		$this->dbConn = $dbConn;
+		$this->logger = $logger;
+	}
+
+	/**
+	 * converts data base data into PHP native, proper types as defined by
+	 * IComment interface.
+	 *
+	 * @param array $data
+	 * @return array
+	 */
+	protected function normalizeDatabaseData(array $data) {
+		$data['id'] = strval($data['id']);
+		$data['parent_id'] = strval($data['parent_id']);
+		$data['topmost_parent_id'] = strval($data['topmost_parent_id']);
+		$data['creation_timestamp'] = new \DateTime($data['creation_timestamp']);
+		$data['latest_child_timestamp'] = new \DateTime($data['latest_child_timestamp']);
+		$data['children_count'] = intval($data['children_count']);
+		return $data;
+	}
+
+	/**
+	 * prepares a comment for an insert or update operation after making sure
+	 * all necessary fields have a value assigned.
+	 *
+	 * @param IComment $comment
+	 * @return IComment returns the same updated IComment instance as provided
+	 *                  by parameter for convenience
+	 * @throws \UnexpectedValueException
+	 */
+	protected function prepareCommentForDatabaseWrite(IComment $comment) {
+		if(    !$comment->getActorType()
+			|| !$comment->getActorId()
+			|| !$comment->getObjectType()
+			|| !$comment->getObjectId()
+			|| !$comment->getVerb()
+		) {
+			throw new \UnexpectedValueException('Actor, Object and Verb information must be provided for saving');
+		}
+
+		if($comment->getId() === '') {
+			$comment->setChildrenCount(0);
+			$comment->setLatestChildDateTime(new \DateTime('0000-00-00 00:00:00', new \DateTimeZone('UTC')));
+			$comment->setLatestChildDateTime(null);
+		}
+
+		if(is_null($comment->getCreationDateTime())) {
+			$comment->setCreationDateTime(new \DateTime());
+		}
+
+		if($comment->getParentId() !== '0') {
+			$comment->setTopmostParentId($this->determineTopmostParentId($comment->getParentId()));
+		} else {
+			$comment->setTopmostParentId('0');
+		}
+
+		$this->cache($comment);
+
+		return $comment;
+	}
+
+	/**
+	 * returns the topmost parent id of a given comment identified by ID
+	 *
+	 * @param string $id
+	 * @return string
+	 * @throws NotFoundException
+	 */
+	protected function determineTopmostParentId($id) {
+		$comment = $this->get($id);
+		if($comment->getParentId() === '0') {
+			return $comment->getId();
+		} else {
+			return $this->determineTopmostParentId($comment->getId());
+		}
+	}
+
+	/**
+	 * updates child information of a comment
+	 *
+	 * @param string	$id
+	 * @param \DateTime	$cDateTime	the date time of the most recent child
+	 * @throws NotFoundException
+	 */
+	protected function updateChildrenInformation($id, \DateTime $cDateTime) {
+		$qb = $this->dbConn->getQueryBuilder();
+		$query = $qb->select($qb->createFunction('COUNT(`id`)'))
+				->from('comments')
+				->where($qb->expr()->eq('parent_id', $qb->createParameter('id')))
+				->setParameter('id', $id);
+
+		$resultStatement = $query->execute();
+		$data = $resultStatement->fetch(\PDO::FETCH_NUM);
+		$resultStatement->closeCursor();
+		$children = intval($data[0]);
+
+		$comment = $this->get($id);
+		$comment->setChildrenCount($children);
+		$comment->setLatestChildDateTime($cDateTime);
+		$this->save($comment);
+	}
+
+	/**
+	 * Tests whether actor or object type and id parameters are acceptable.
+	 * Throws exception if not.
+	 *
+	 * @param string $role
+	 * @param string $type
+	 * @param string $id
+	 * @throws \InvalidArgumentException
+	 */
+	protected function checkRoleParameters($role, $type, $id) {
+		if(
+			   !is_string($type) || empty($type)
+			|| !is_string($id) || empty($id)
+		) {
+			throw new \InvalidArgumentException($role . ' parameters must be string and not empty');
+		}
+	}
+
+	/**
+	 * run-time caches a comment
+	 *
+	 * @param IComment $comment
+	 */
+	protected function cache(IComment $comment) {
+		$id = $comment->getId();
+		if(empty($id)) {
+			return;
+		}
+		$this->commentsCache[strval($id)] = $comment;
+	}
+
+	/**
+	 * removes an entry from the comments run time cache
+	 *
+	 * @param mixed $id the comment's id
+	 */
+	protected function uncache($id) {
+		$id = strval($id);
+		if (isset($this->commentsCache[$id])) {
+			unset($this->commentsCache[$id]);
+		}
+	}
+
+	/**
+	 * returns a comment instance
+	 *
+	 * @param string $id the ID of the comment
+	 * @return IComment
+	 * @throws NotFoundException
+	 * @throws \InvalidArgumentException
+	 * @since 9.0.0
+	 */
+	public function get($id) {
+		if(intval($id) === 0) {
+			throw new \InvalidArgumentException('IDs must be translatable to a number in this implementation.');
+		}
+
+		if(isset($this->commentsCache[$id])) {
+			return $this->commentsCache[$id];
+		}
+
+		$qb = $this->dbConn->getQueryBuilder();
+		$resultStatement = $qb->select('*')
+			->from('comments')
+			->where($qb->expr()->eq('id', $qb->createParameter('id')))
+			->setParameter('id', $id, \PDO::PARAM_INT)
+			->execute();
+
+		$data = $resultStatement->fetch();
+		$resultStatement->closeCursor();
+		if(!$data) {
+			throw new NotFoundException();
+		}
+
+		$comment = new Comment($this->normalizeDatabaseData($data));
+		$this->cache($comment);
+		return $comment;
+	}
+
+	/**
+	 * returns the comment specified by the id and all it's child comments.
+	 * At this point of time, we do only support one level depth.
+	 *
+	 * @param string $id
+	 * @param int $limit max number of entries to return, 0 returns all
+	 * @param int $offset the start entry
+	 * @return array
+	 * @since 9.0.0
+	 *
+	 * The return array looks like this
+	 * [
+	 *   'comment' => IComment, // root comment
+	 *   'replies' =>
+	 *   [
+	 *     0 =>
+	 *     [
+	 *       'comment' => IComment,
+	 *       'replies' => []
+	 *     ]
+	 *     1 =>
+	 *     [
+	 *       'comment' => IComment,
+	 *       'replies'=> []
+	 *     ],
+	 *     …
+	 *   ]
+	 * ]
+	 */
+	public function getTree($id, $limit = 0, $offset = 0) {
+		$tree = [];
+		$tree['comment'] = $this->get($id);
+		$tree['replies'] = [];
+
+		$qb = $this->dbConn->getQueryBuilder();
+		$query = $qb->select('*')
+				->from('comments')
+				->where($qb->expr()->eq('topmost_parent_id', $qb->createParameter('id')))
+				->orderBy('creation_timestamp', 'DESC')
+				->setParameter('id', $id);
+
+		if($limit > 0) {
+			$query->setMaxResults($limit);
+		}
+		if($offset > 0) {
+			$query->setFirstResult($offset);
+		}
+
+		$resultStatement = $query->execute();
+		while($data = $resultStatement->fetch()) {
+			$comment = new Comment($this->normalizeDatabaseData($data));
+			$this->cache($comment);
+			$tree['replies'][] = [
+				'comment' => $comment,
+				'replies' => []
+			];
+		}
+		$resultStatement->closeCursor();
+
+		return $tree;
+	}
+
+	/**
+	 * returns comments for a specific object (e.g. a file).
+	 *
+	 * The sort order is always newest to oldest.
+	 *
+	 * @param string $objectType the object type, e.g. 'files'
+	 * @param string $objectId the id of the object
+	 * @param int $limit optional, number of maximum comments to be returned. if
+	 * not specified, all comments are returned.
+	 * @param int $offset optional, starting point
+	 * @param \DateTime $notOlderThan optional, timestamp of the oldest comments
+	 * that may be returned
+	 * @return IComment[]
+	 * @since 9.0.0
+	 */
+	public function getForObject(
+			$objectType,
+			$objectId,
+			$limit = 0,
+			$offset = 0,
+			\DateTime $notOlderThan = null
+	) {
+		$comments = [];
+
+		$qb = $this->dbConn->getQueryBuilder();
+		$query = $qb->select('*')
+				->from('comments')
+				->where($qb->expr()->eq('object_type', $qb->createParameter('type')))
+				->andWhere($qb->expr()->eq('object_id', $qb->createParameter('id')))
+				->orderBy('creation_timestamp', 'DESC')
+				->setParameter('type', $objectType)
+				->setParameter('id', $objectId);
+
+		if($limit > 0) {
+			$query->setMaxResults($limit);
+		}
+		if($offset > 0) {
+			$query->setFirstResult($offset);
+		}
+		if(!is_null($notOlderThan)) {
+			$query
+				->andWhere($qb->expr()->gt('creation_timestamp', $qb->createParameter('notOlderThan')))
+				->setParameter('notOlderThan', $notOlderThan, 'datetime');
+		}
+
+		$resultStatement = $query->execute();
+		while($data = $resultStatement->fetch()) {
+			$comment = new Comment($this->normalizeDatabaseData($data));
+			$this->cache($comment);
+			$comments[] = $comment;
+		}
+		$resultStatement->closeCursor();
+
+		return $comments;
+	}
+
+	/**
+	 * @param $objectType string the object type, e.g. 'files'
+	 * @param $objectId string the id of the object
+	 * @return Int
+	 * @since 9.0.0
+	 */
+	public function getNumberOfCommentsForObject($objectType, $objectId) {
+		$qb = $this->dbConn->getQueryBuilder();
+		$query = $qb->select($qb->createFunction('COUNT(`id`)'))
+				->from('comments')
+				->where($qb->expr()->eq('object_type', $qb->createParameter('type')))
+				->andWhere($qb->expr()->eq('object_id', $qb->createParameter('id')))
+				->setParameter('type', $objectType)
+				->setParameter('id', $objectId);
+
+		$resultStatement = $query->execute();
+		$data = $resultStatement->fetch(\PDO::FETCH_NUM);
+		$resultStatement->closeCursor();
+		return intval($data[0]);
+	}
+
+	/**
+	 * creates a new comment and returns it. At this point of time, it is not
+	 * saved in the used data storage. Use save() after setting other fields
+	 * of the comment (e.g. message or verb).
+	 *
+	 * @param string $actorType the actor type (e.g. 'user')
+	 * @param string $actorId a user id
+	 * @param string $objectType the object type the comment is attached to
+	 * @param string $objectId the object id the comment is attached to
+	 * @return IComment
+	 * @since 9.0.0
+	 */
+	public function create($actorType, $actorId, $objectType, $objectId) {
+		$comment = new Comment();
+		$comment
+			->setActor($actorType, $actorId)
+			->setObject($objectType, $objectId);
+		return $comment;
+	}
+
+	/**
+	 * permanently deletes the comment specified by the ID
+	 *
+	 * When the comment has child comments, their parent ID will be changed to
+	 * the parent ID of the item that is to be deleted.
+	 *
+	 * @param string $id
+	 * @return bool
+	 * @throws \InvalidArgumentException
+	 * @since 9.0.0
+	 */
+	public function delete($id) {
+		if(!is_string($id)) {
+			throw new \InvalidArgumentException('Parameter must be string');
+		}
+
+		$qb = $this->dbConn->getQueryBuilder();
+		$query = $qb->delete('comments')
+			->where($qb->expr()->eq('id', $qb->createParameter('id')))
+			->setParameter('id', $id);
+
+		try {
+			$affectedRows = $query->execute();
+			$this->uncache($id);
+		} catch (DriverException $e) {
+			$this->logger->logException($e, ['app' => 'core_comments']);
+			return false;
+		}
+		return ($affectedRows > 0);
+	}
+
+	/**
+	 * saves the comment permanently and returns it
+	 *
+	 * if the supplied comment has an empty ID, a new entry comment will be
+	 * saved and the instance updated with the new ID.
+	 *
+	 * Otherwise, an existing comment will be updated.
+	 *
+	 * Throws NotFoundException when a comment that is to be updated does not
+	 * exist anymore at this point of time.
+	 *
+	 * @param IComment $comment
+	 * @return bool
+	 * @throws NotFoundException
+	 * @since 9.0.0
+	 */
+	public function save(IComment $comment) {
+		if($this->prepareCommentForDatabaseWrite($comment)->getId() === '') {
+			$result = $this->insert($comment);
+		} else {
+			$result = $this->update($comment);
+		}
+
+		if($result && !!$comment->getParentId()) {
+			$this->updateChildrenInformation(
+					$comment->getParentId(),
+					$comment->getCreationDateTime()
+			);
+			$this->cache($comment);
+		}
+
+		return $result;
+	}
+
+	/**
+	 * inserts the provided comment in the database
+	 *
+	 * @param IComment $comment
+	 * @return bool
+	 */
+	protected function insert(IComment &$comment) {
+		$qb = $this->dbConn->getQueryBuilder();
+		$affectedRows = $qb
+			->insert('comments')
+			->values([
+				'parent_id'					=> $qb->createNamedParameter($comment->getParentId()),
+				'topmost_parent_id' 		=> $qb->createNamedParameter($comment->getTopmostParentId()),
+				'children_count' 			=> $qb->createNamedParameter($comment->getChildrenCount()),
+				'actor_type' 				=> $qb->createNamedParameter($comment->getActorType()),
+				'actor_id' 					=> $qb->createNamedParameter($comment->getActorId()),
+				'message' 					=> $qb->createNamedParameter($comment->getMessage()),
+				'verb' 						=> $qb->createNamedParameter($comment->getVerb()),
+				'creation_timestamp' 		=> $qb->createNamedParameter($comment->getCreationDateTime(), 'datetime'),
+				'latest_child_timestamp'	=> $qb->createNamedParameter($comment->getLatestChildDateTime(), 'datetime'),
+				'object_type' 				=> $qb->createNamedParameter($comment->getObjectType()),
+				'object_id' 				=> $qb->createNamedParameter($comment->getObjectId()),
+			])
+			->execute();
+
+		if ($affectedRows > 0) {
+			$comment->setId(strval($qb->getLastInsertId()));
+		}
+
+		return $affectedRows > 0;
+	}
+
+	/**
+	 * updates a Comment data row
+	 *
+	 * @param IComment $comment
+	 * @return bool
+	 * @throws NotFoundException
+	 */
+	protected function update(IComment $comment) {
+		$qb = $this->dbConn->getQueryBuilder();
+		$affectedRows = $qb
+			->update('comments')
+				->set('parent_id',				$qb->createNamedParameter($comment->getParentId()))
+				->set('topmost_parent_id', 		$qb->createNamedParameter($comment->getTopmostParentId()))
+				->set('children_count',			$qb->createNamedParameter($comment->getChildrenCount()))
+				->set('actor_type', 			$qb->createNamedParameter($comment->getActorType()))
+				->set('actor_id', 				$qb->createNamedParameter($comment->getActorId()))
+				->set('message',				$qb->createNamedParameter($comment->getMessage()))
+				->set('verb',					$qb->createNamedParameter($comment->getVerb()))
+				->set('creation_timestamp',		$qb->createNamedParameter($comment->getCreationDateTime(), 'datetime'))
+				->set('latest_child_timestamp',	$qb->createNamedParameter($comment->getLatestChildDateTime(), 'datetime'))
+				->set('object_type',			$qb->createNamedParameter($comment->getObjectType()))
+				->set('object_id',				$qb->createNamedParameter($comment->getObjectId()))
+			->where($qb->expr()->eq('id', $qb->createParameter('id')))
+			->setParameter('id', $comment->getId())
+			->execute();
+
+		if($affectedRows === 0) {
+			throw new NotFoundException('Comment to update does ceased to exist');
+		}
+
+		return $affectedRows > 0;
+	}
+
+	/**
+	 * removes references to specific actor (e.g. on user delete) of a comment.
+	 * The comment itself must not get lost/deleted.
+	 *
+	 * @param string $actorType the actor type (e.g. 'user')
+	 * @param string $actorId a user id
+	 * @return boolean
+	 * @since 9.0.0
+	 */
+	public function deleteReferencesOfActor($actorType, $actorId) {
+		$this->checkRoleParameters('Actor', $actorType, $actorId);
+
+		$qb = $this->dbConn->getQueryBuilder();
+		$affectedRows = $qb
+			->update('comments')
+			->set('actor_type',	$qb->createNamedParameter(ICommentsManager::DELETED_USER))
+			->set('actor_id',	$qb->createNamedParameter(ICommentsManager::DELETED_USER))
+			->where($qb->expr()->eq('actor_type', $qb->createParameter('type')))
+			->andWhere($qb->expr()->eq('actor_id', $qb->createParameter('id')))
+			->setParameter('type', $actorType)
+			->setParameter('id', $actorId)
+			->execute();
+
+		$this->commentsCache = [];
+
+		return is_int($affectedRows);
+	}
+
+	/**
+	 * deletes all comments made of a specific object (e.g. on file delete)
+	 *
+	 * @param string $objectType the object type (e.g. 'file')
+	 * @param string $objectId e.g. the file id
+	 * @return boolean
+	 * @since 9.0.0
+	 */
+	public function deleteCommentsAtObject($objectType, $objectId) {
+		$this->checkRoleParameters('Object', $objectType, $objectId);
+
+		$qb = $this->dbConn->getQueryBuilder();
+		$affectedRows = $qb
+			->delete('comments')
+			->where($qb->expr()->eq('object_type', $qb->createParameter('type')))
+			->andWhere($qb->expr()->eq('object_id', $qb->createParameter('id')))
+			->setParameter('type', $objectType)
+			->setParameter('id', $objectId)
+			->execute();
+
+		$this->commentsCache = [];
+
+		return is_int($affectedRows);
+	}
+}
diff --git a/lib/private/comments/managerfactory.php b/lib/private/comments/managerfactory.php
new file mode 100644
index 00000000000..41978d0cf4b
--- /dev/null
+++ b/lib/private/comments/managerfactory.php
@@ -0,0 +1,23 @@
+<?php
+
+namespace OC\Comments;
+
+use OCP\Comments\ICommentsManager;
+use OCP\Comments\ICommentsManagerFactory;
+
+
+class ManagerFactory implements ICommentsManagerFactory {
+
+	/**
+	 * creates and returns an instance of the ICommentsManager
+	 *
+	 * @return ICommentsManager
+	 * @since 9.0.0
+	 */
+	public function getManager() {
+		return new Manager(
+			\OC::$server->getDatabaseConnection(),
+			\OC::$server->getLogger()
+		);
+	}
+}
diff --git a/lib/private/server.php b/lib/private/server.php
index 6692e6f6bbf..8439500706d 100644
--- a/lib/private/server.php
+++ b/lib/private/server.php
@@ -528,6 +528,13 @@ class Server extends SimpleContainer implements IServerContainer {
 			});
 			return $manager;
 		});
+		$this->registerService('CommentsManager', function(Server $c) {
+			$config = $c->getConfig();
+			$factoryClass = $config->getSystemValue('comments.managerFactory', '\OC\Comments\ManagerFactory');
+			/** @var \OCP\Comments\ICommentsManagerFactory $factory */
+			$factory = new $factoryClass();
+			return $factory->getManager();
+		});
 		$this->registerService('EventDispatcher', function() {
 			return new EventDispatcher();
 		});
@@ -1122,6 +1129,13 @@ class Server extends SimpleContainer implements IServerContainer {
 	}
 
 	/**
+	 * @return \OCP\Comments\ICommentsManager
+	 */
+	public function getCommentsManager() {
+		return $this->query('CommentsManager');
+	}
+
+	/**
 	 * @return \OC\IntegrityCheck\Checker
 	 */
 	public function getIntegrityCodeChecker() {
diff --git a/lib/private/user/user.php b/lib/private/user/user.php
index d827097ee39..6c89dd06f77 100644
--- a/lib/private/user/user.php
+++ b/lib/private/user/user.php
@@ -189,6 +189,8 @@ class User implements IUser {
 
 			// Delete the users entry in the storage table
 			\OC\Files\Cache\Storage::remove('home::' . $this->uid);
+
+			\OC::$server->getCommentsManager()->deleteReferencesOfActor('user', $this->uid);
 		}
 
 		if ($this->emitter) {