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Status:

OVERVIEW

This document describes the main design and implementation decisions behind the "Group Mentions” feature. This feature provides ways for a MM user to mention groups and notify their members (and invite the ones that are not in the channel to the channel).

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“Group-constrained” - when a group is linked to a channel or team and the syncing of its group members is turned on.

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We can split the group mentioning flow into two phases: Build Suggestions and Notify Members. In the Build Suggestions phase we build the suggestions list that is displayed in the channel UI when the user enters the “@*” text in the channel textbox. In the Notify Members phase we sedn the notifications to the members of the groups being selected in the previous phase. We will detail the design and the API, storage and client supporting changes for both of them.

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A channel or a team can be in one of two states :

1. constrained to the group(s)

2. not constrained by any group.

Depending if the current channel and/or the containing team is group constrained , we can have the following group-mentioning cases:

1. If the current channel is constrained by the group(s), the user in the channel can only mention one of these groups.

2. Otherwise, if the current team is constrained to by one or more groups, the user can only mention one or more of these groups.

3. If neither the current channel is constrained, nor the current team, then the user can mention any group constrained to any channel/group in the system. (currently all groups in MM are linked groups).

While we currently do not have a good grasp estimate of how many groups we can have in an org, we made the assumption that the number is small enough where we could fetch them from the server more than once during a user session (we somewhat optimize this action by retrieving only the mentionable ones). The group mention flow is initiated from a channel's textbox; it is an expensive operation to repeatedly fetch the group(s) from the server as the user types - we will fetch the groups and populate the client state (depending if the channel/team is group-constrained or not) once per team initialization (which means that if we switch teams in the work session we will fetch the teams from the server again).

Future Work: Ideally, We are exploring way to ensure the groups will need to be fetched only once, at server start, not at every team change (and then only updated based on group-related System Console actions). Later this set is updated based on user’s actions (groups removed, etc.)

Duplicate group names

When we enable group mentioning on a group in the System Console, we are also generating the actual group name “group name” property from the group’s display name “display name” (e.g. from display name: “software developers” to ; group name: “@software-developers”). This happens at the server-side and since we enforce the uniqueness of the name column in the UserGroups table, there is a potential of erroring by error and throwing a SQL exception if there is already a group with the same name already stored. Future Work: Fully  We address the duplicate group name case . One solution would be to surface by surfacing the duplicate error in the UI and allow allowing the user to specify a different (custom) group name if the current one is a duplicate of another.

Groups with no team members

When we build the list of groups to mention, the groups are added to the list if the channel/team are group-constrained or not. However, it could be that for some of these groups none of their members are members of the current team. Since the members of these groups are not going to be notified, one solution is to avoid selecting them for inclusion in the mentions suggestion list to begin with. The current plan is to include these groups in the suggestion list.

Future Work: Filter out the groups that have no members in the current team from inclusion in the mentions suggestion list.  Another proposed solution is to add an invite flow:  “invite them now” quick link.

Ticket: https://mattermost.atlassian.net/browse/MM-23816

UI/X (Webapp)

Group Mention Settings Toggle Panel

• we will add a new “Group Mention Settings” toggle widget containing a toggle component in the Group Configuration details panel in the System Console. We will change not commit the update of the group states on the server at every UI toggle action (there is no Save action).

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• object at the server until the user clicks on the Save button in the panel - until then, the group is in a draft state. We will validate and warn the user for the following conditions:

  • group name is empty

  • group name contains invalid characters (TBD the exact set of characters allowed).

Channel Textbox Suggestions List

• when displaying the group mention in the suggestion list, we plan to will include the group group’s name and the group display name. There has been discussion to also display the member count (e.g. : “@software-developers - software developers - 4 members”)

Future work:  Add a member count to the @group-name like : “@software-developers - 4 members”

• Software Developers”.

UI/X (Redux)

Selectors:

• searchAssociatedGroupsForReferenceLocal - allows for searching of mentionable groups based on the user entered text

• getAssociatedGroupsForReference - returns the full list of groups that constrain a channel and/or team (or not), base don the criteria mentioned above. If the current user’s role does not have USE_GROUP_MENTIONS permission, it will return an empty list.

• getGroupsAssociatedToTeamForReference- returns the list of groups that constrain a team

• getGroupsAssociatedToChannelForReference - returns the list of groups that constrain a channel

• getAllAssociatedGroupsForReference - returns the list of groups that constrain a channel or team in the system

Actions:

• getGroups - returns the list of groups from the server filtered by filter_allow_reference flag

• patchGroup - patches a group with an new name or allow_reference property

• getAllGroupsAssociatedToChannelsInTeam - for every channel that is constrained by one or more groups, returns the corresponding list of groups, indexed by the channel’s id.

REST API

• we will add the following new endpoints:

Team : …/ groups_by_channels  getGroupsAssociatedToChannelsByTeam(GET) - returns for a team, a map of channels constrained by groups and the corresponding groups.

• we will update augment the following GetGroupsgetGroups* API endpoints with the additional filter_allow_reference filter (default is false), to be able to retrieve from the server only the groups that are enabled for mentions.

GetGroupsByChannel

GetGroupsByTeam

GetGroupsAssociatedToChannelsByTeam

GetGroupsgetGroupsByChannel, getGroupsByTeam, getGroupsAssociatedToChannelsByTeam, getGroups

Storage

• we will add a new SQL stored-procedure:  getGroupsAssociatedToChannelsByTeam - for every channel that is constrained by one or more groups, retrieves the corresponding list of groups, indexed by the channel’s id.

Tickets

Display group mentions in suggestions list in the main channel textbox

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• The first step added will be to check if the user creating the post and has access to PERMISSION_USE_GROUP_MENTIONS, if not then the behaviour behavior of SendNotifications will be unchanged

• If group mentions are enabled then all groups that have AllowReference = 1 will be added to memory

• The ExplicitMentions struct will have a new attribute GroupMentions to store the groups mentioned by the Post.Message.

• Once all groups are added to the GroupMentions map, group members that exist in the channel will be added to the Mentions map as confirmed mentions in the channel.

• Group members that exist in the team but not in the channel will be added to OtherPotentialMentions and will have an invite message generated for them using the existing logic.

• If there are no group members in the team that the message is sent to, a system message will return be sent, letting the user know that the group mentioned has no members in the current team.

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• in the notification phase, when the aggregated number of group members to mention is above a certain threshold N(=5), we are showing displaying a warning modal  (see wireframe), the text message in the modal includes specifies the user count from the largest group in the set of groups selected in the collectionfirst phase. This is a compromise solution, due to performance constraints - fetching the accurate count, including membership overlaps, from the server would introduce a delay in sending the notificationsee below.

• For example, if we mention @developers and @board, where @developers has 10 users within the channel while @board only has 2 members in the channel, the warning modal will warn the user that she is about to notify @developers with 10 members in the channel.
  If two groups have common users the total count to be displayed by the dialog would have to be the union of members for each group within the channel. This can be done but at a significant performance cost (groups can have a large number of members).

Future work: Investigate a better solution?

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• The markdown component will be modified to use getAllUserMentionKeys which contains the union of `getCurrentUserMentionKeys and getCurrentUserGroupMentionKeys. This will ensure that group names will be highlighted for the user as expected.

• The existing admin setting enableConfirmNotificationsToChannel will be used to determine if the warning modal should show up if a group has more than N members in the channel.

• Upon visiting a channel all the groups that have members within that channel can be retrieved by using the channelMemberCountsByGroup selector.

• A utility function groupsMentionedInText will be added to get all the groups mentioned in a message before sending.

• All the groups being mentioned will be retrieved from the Redux state and then the one with the largest number channel members will be selected and its member count be used to display the number of users being notified. However, if groups are being mentioned alongside @all or @channel, then the total number of channel members - 1 will be used instead.

UI/X(Redux)

• A new selector will be added to get the list of groups that the current user can be mentioned by: getCurrentUserGroupMentionKeys this - it will be used to determine which @group mentions should be highlighted in the chat facing UI. This selector will be used inside of getAllUserMentionKeys to return where we merge its set with the result merged with of calling getCurrentUserMentionKeys (which contains regular mentions such as first name / user name etc).

• New actions and selectors for getChannelMemberCountsByGroup have been added, which take a channelID and a boolean includeTimezones flag as arguments and returns a list of all groups with members within the channel and number of members in that channel. If includeTimezones is true the function also returns the number of unique timezones for the users in that group.

REST API

we will add the following new endpoints:

channel: “.../ member_counts_by_group/" channelMemberCountsByGroup` (GET)

since we extend the range of calls to the GetGroups* methods from the SystemConsole to the chat-facing area we will remove the existing permission check from the following API calls:

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GetGroups

GetGroupsForTeam

…getGroups, getGroupsByTeam

The USE_GROUP_MENTIONSpermission check is being done now in Redux, where we check the current user’s permission to fetch the mentionable groups.

Storage:

• we will add the following new stored procedures:

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GetMemberUsersNotInChannel - returns a slice of users that are members of a group that exist in the team that the channel belongs to but do not exist in the channel. The intersection of (users in team) & (users in group) & (users not in channel)

Tickets

Group Mentions - Show a confirmation dialog when mentioning a group with too many users

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• we will add a new column to the UserGroups table to tag the groups that are enabled for mentioning:

    AllowReference     AllowReference : boolean

Permissions

• we will add a new permission USEpermission USE_GROUP_MENTIONS MENTIONS - this allows us to  

Tickets

Create use_group_mentions permission

https://mattermost.atlassian.net/browse/MM-23019

Websockets updatesTicket: Ensure websockets are updating the referenceable groups (et al) in Redux for group-mentions

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