Search: Fix only searching for folder id zero (#44175)

Fixes so that searching for folder id zero in folder/dashboard search returns 
dashboards located in the general folder and not including all folders as it 
did before.

Fixes #40273

pkg/services/sqlstore/dashboard.go

@@ -305,7 +305,7 @@ func (ss *SQLStore) findDashboards(ctx context.Context, query *search.FindPersis
 	}
 
 	if len(query.FolderIds) > 0 {
-		filters = append(filters, searchstore.FolderFilter{IDs: query.FolderIds})
+		filters = append(filters, searchstore.FolderFilter{Dialect: dialect, IDs: query.FolderIds})
 	}
 
 	var res []DashboardSearchProjection

pkg/services/sqlstore/dashboard_test.go

@@ -384,6 +384,24 @@ func TestDashboardDataAccess(t *testing.T) {
 		require.Equal(t, hit.FolderURL, fmt.Sprintf("/dashboards/f/%s/%s", savedFolder.Uid, savedFolder.Slug))
 	})
 
+	t.Run("Should be able to search for general folder's children", func(t *testing.T) {
+		setup()
+		query := search.FindPersistedDashboardsQuery{
+			OrgId:        1,
+			FolderIds:    []int64{0},
+			SignedInUser: &models.SignedInUser{OrgId: 1, OrgRole: models.ROLE_EDITOR},
+		}
+
+		err := sqlStore.SearchDashboards(context.Background(), &query)
+		require.NoError(t, err)
+
+		require.Equal(t, len(query.Result), 1)
+		hit := query.Result[0]
+		require.Equal(t, savedDash2.Id, hit.ID)
+		require.Equal(t, fmt.Sprintf("/d/%s/%s", savedDash2.Uid, savedDash2.Slug), hit.URL)
+		require.Equal(t, int64(0), hit.FolderID)
+	})
+
 	t.Run("Should be able to search for dashboard by dashboard ids", func(t *testing.T) {
 		setup()
 		query := search.FindPersistedDashboardsQuery{

pkg/services/sqlstore/searchstore/filters.go

@@ -87,10 +87,16 @@ func (f TitleFilter) Where() (string, []interface{}) {
 }
 
 type FolderFilter struct {
-	IDs []int64
+	Dialect migrator.Dialect
+	IDs     []int64
 }
 
 func (f FolderFilter) Where() (string, []interface{}) {
+	if len(f.IDs) == 1 && f.IDs[0] == 0 {
+		sql := fmt.Sprintf("dashboard.folder_id = 0 AND dashboard.is_folder = %s", f.Dialect.BooleanStr(false))
+		return sql, []interface{}{}
+	}
+
 	return sqlIDin("dashboard.folder_id", f.IDs)
 }