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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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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.

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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 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 5 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 explained further -see 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 explain that you are warn the user that she is about to notify @developers with 10 members in the channel.
  If two groups have repeating common users the total count shown to be displayed by the dialog would have to be the union of members for each group within the channel. This would cause can be done but at a significant performance regression and cannot be done for the MVPcost (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 5 N members in the channel.

• Upon visiting a channel all the groups that have members within that channel will now be available in 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 most largest number channel members will be grabbed 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.

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• 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.

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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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