Backend implementation

Database structure

https://excalidraw.com/#json=6583019510956032,3U8twxl8OgyBScD1yXFTXQ

New additions are colored green.

Table	Column	Definition
Channels	TotalMsgCountRoot	Total number of root messages
ChannelMembers	MsgCountRoot	Number of seen root messages
	MentionCountRoot	Number of unread mentions in root messages
Threads	PostId	Id of the root post
	ChannelId
	ReplyCount	Number or reply posts in this thread
	LastReplyAt	Timestamp of the last reply
	Participants	json array of all thread member IDs
ThreadMemberships	PostId	Id of the root post
	UserId	Id of the user
	Following	Is the thread followed
	UnreadMentions	Number of unread mentions for this user in the thread
	LastViewed	Timestamp of when the thread was last viewed
	LastUpdated	Timestamp of the last change to the thread (follow state, mentions, etc)

API

New APIs

Path	Method	Description
api/v4/users/{user_id}/teams/{team_id}/threads	GET	Return threads that the user is following
api/v4/users/{user_id}/teams/{team_id}/threads/read	PUT	Mark all threads as read
api/v4/users/{user_id}/teams/{team_id}/{thread_id}	GET	Get one thread by Id
api/v4/users/{user_id}/teams/{team_id}/{thread_id}/following	PUT	Start following a thread
api/v4/users/{user_id}/teams/{team_id}/{thread_id}/following	DELETE	Stop following a thread
api/v4/users/{user_id}/teams/{team_id}/{thread_id}/read/{timestamp}	PUT	Change ‘read’ state of a thread based on the timestamp

Updated APIs

All ‘get posts’ methods, i.e.:
/api/v4/users/{user_id}/channels/{channel_id}/posts/unread
/api/v4/channels/{channel_id}/posts
/api/v4/posts/{post_id}/thread

Will receive additional optional query parameter: collapsedThreads=true
Optionally, extendedCollapsedThreads=true can be provided to enrich participants array

In this mode, the output of these API calls will change, instead of returning all posts, only top-level posts will be returned, and for those posts that have replies (i.e. threads), additional fields will be added to the output:

participants - array of user IDs (used to show avatars under the thread info in the channel): [{id:"zxxxx", id:"xcccvbs"}] or if extendedCollapsedThreads is set it will return the full user objects
reply_count - amount of replies
followed - if current user is following this thread
last_reply_at - timestamp of last reply
unreadReplies - unread replies in this thread
unreadMentions - unread mentions in this thread

Config

ServiceSettings.CollapsedThreads

Defaults to ‘disabled’.
Can also be ‘default_on’ or ‘default_off’ to set thread preference for users.
User can override via user preference: ‘collapsed_threads_settings.collapsed_threads_enabled’

ServiceSettings.ThreadAutoFollow

Defaults to ‘true’.
Controls if the threads are autofollowed when:

Somebody replies to your post
You are mentioned in a thread
When someone replies to a root post you are mentioned in

Websocket events

New events

thread_updated

issued when there is a change in a thread (new post). includes thread details in ‘thread’ field.

thread_follow_changed

issued when a thread ‘followed’ state is changed
includes ‘thread_id’ and ‘state’ fields, ‘state’ is true/false indicating following/unfollowed

thread_read_changed

issued when a thread ‘read’ state is changed
includes ‘thread_id’ and ‘timestamp’ fields, ‘timestamp’ indicates the time to which the thread was reset to.
if ‘thread_id’ is not included - even applies to ALL user threads

Updated events

posted/post_edited/post_deleted

Additional ‘following’ boolean will be added