MM-49547: Handle Top DM case for deleted second user (#22049)

* Ignore archived DM channels with deleted second user

* Add tests

* Add store test

* Add error check for post delete in test

---------

Co-authored-by: Mattermost Build <build@mattermost.com>

app/post_test.go

@@ -3292,4 +3292,19 @@ func TestGetTopDMsForUserSince(t *testing.T) {
 		require.Equal(t, topDMs.Items[0].SecondParticipant.Id, u3.Id)
 		require.Equal(t, topDMs.Items[0].MessageCount, int64(4))
 	})
+
+	t.Run("topDMs will not consider deleted second user", func(t *testing.T) {
+		// u4 only takes part in one conversation
+		topDMs, err := th.App.GetTopDMsForUserSince(u4.Id, &model.InsightsOpts{StartUnixMilli: 100, Page: 0, PerPage: 100})
+		require.Nil(t, err)
+		// len of topDMs.Items should be 1
+		require.Len(t, topDMs.Items, 1)
+		// delete user3
+		err = th.App.PermanentDeleteUser(th.Context, u3)
+		require.Nil(t, err)
+		topDMs, err = th.App.GetTopDMsForUserSince(u4.Id, &model.InsightsOpts{StartUnixMilli: 100, Page: 0, PerPage: 100})
+		require.Nil(t, err)
+		// len of topDMs.Items should be 0 since u3 is deleted
+		require.Len(t, topDMs.Items, 0)
+	})
 }

store/sqlstore/post_store.go

@@ -3170,10 +3170,14 @@ func (s *SqlPostStore) GetTopDMsForUserSince(userID string, since int64, offset
 			},
 		}).GroupBy("vch.id")
 
-	topDMsBuilder = topDMsBuilder.OrderBy("MessageCount DESC").Limit(uint64(limit + 1)).Offset(uint64(offset))
+	// following where clause filters out all archived DMs with "deleted" users, that has only 1 user-id in Participants column.
+	archivedDMsFilter := s.getQueryBuilder().Select("MessageCount", "Participants", "ChannelId").FromSelect(topDMsBuilder, "top_dms").
+		Where(sq.Expr("POSITION(',' IN Participants) > 0"))
+
+	archivedDMsFilter = archivedDMsFilter.OrderBy("MessageCount DESC").Limit(uint64(limit + 1)).Offset(uint64(offset))
 
 	topDMs := make([]*model.TopDM, 0)
-	sql, args, err := topDMsBuilder.ToSql()
+	sql, args, err := archivedDMsFilter.ToSql()
 	if err != nil {
 		return nil, errors.Wrap(err, "GetTopDMsForUserSince_ToSql")
 	}

store/storetest/post_store.go

@@ -4901,7 +4901,7 @@ func testGetTopDMsForUserSince(t *testing.T, ss store.Store, s SqlStore) {
 		require.NoError(t, err)
 	}
 	// for u4-u3: 4 posts
-	_, err = ss.Post().Save(&model.Post{
+	u3u4Post1, err := ss.Post().Save(&model.Post{
 		ChannelId: chUser3User4.Id,
 		UserId:    u3.Id,
 	})
@@ -4911,7 +4911,7 @@ func testGetTopDMsForUserSince(t *testing.T, ss store.Store, s SqlStore) {
 		UserId:    u4.Id,
 	})
 	require.NoError(t, err)
-	_, err = ss.Post().Save(&model.Post{
+	u3u4Post2, err := ss.Post().Save(&model.Post{
 		ChannelId: chUser3User4.Id,
 		UserId:    u3.Id,
 	})
@@ -4965,6 +4965,28 @@ func testGetTopDMsForUserSince(t *testing.T, ss store.Store, s SqlStore) {
 		// len of topDMs.Items should be 3
 		require.Len(t, topDMs.Items, 2)
 	})
+	t.Run("topDMs will not consider deleted second user", func(t *testing.T) {
+		// u4 only takes part in one conversation
+		topDMs, err := ss.Post().GetTopDMsForUserSince(u4.Id, 100, 0, 100)
+		require.NoError(t, err)
+		// len of topDMs.Items should be 1
+		require.Len(t, topDMs.Items, 1)
+		// delete user3
+		err = ss.User().PermanentDelete(u3.Id)
+		require.NoError(t, err)
+		// delete user3 posts
+		err = ss.Post().Delete(u3u4Post1.Id, 200, u3.Id)
+		require.NoError(t, err)
+		err = ss.Post().Delete(u3u4Post2.Id, 200, u3.Id)
+		require.NoError(t, err)
+		// delete channel memberships
+		err = ss.Channel().PermanentDeleteMembersByUser(u3.Id)
+		require.NoError(t, err)
+		topDMs, err = ss.Post().GetTopDMsForUserSince(u4.Id, 100, 0, 100)
+		require.NoError(t, err)
+		// len of topDMs.Items should be 0 since u3 is deleted
+		require.Len(t, topDMs.Items, 0)
+	})
 }
 
 func testGetEditHistoryForPost(t *testing.T, ss store.Store) {