Folders: Reduce DB queries when counting and deleting resources under folders (#81153)

* Add folder store method for fetching all folder descendants

* Modify GetDescendantCounts() to fetch folder descendants at once

* Reduce DB calls when counting library panels under dashboard

* Reduce DB calls when counting dashboards under folder

* Reduce DB calls during folder delete

* Modify folder registry to count/delete entities under multiple folders

* Reduce DB calls when counting

* Reduce DB calls when deleting

pkg/services/folder/folderimpl/sqlstore.go

@@ -83,11 +83,20 @@ func (ss *sqlStore) Create(ctx context.Context, cmd folder.CreateFolderCommand)
 	return foldr.WithURL(), err
 }
 
-func (ss *sqlStore) Delete(ctx context.Context, uid string, orgID int64) error {
+func (ss *sqlStore) Delete(ctx context.Context, UIDs []string, orgID int64) error {
+	if len(UIDs) == 0 {
+		return nil
+	}
 	return ss.db.WithDbSession(ctx, func(sess *db.Session) error {
-		_, err := sess.Exec("DELETE FROM folder WHERE uid=? AND org_id=?", uid, orgID)
+		s := fmt.Sprintf("DELETE FROM folder WHERE org_id=? AND uid IN (%s)", strings.Repeat("?, ", len(UIDs)-1)+"?")
+		sqlArgs := make([]any, 0, len(UIDs)+2)
+		sqlArgs = append(sqlArgs, s, orgID)
+		for _, uid := range UIDs {
+			sqlArgs = append(sqlArgs, uid)
+		}
+		_, err := sess.Exec(sqlArgs...)
 		if err != nil {
-			return folder.ErrDatabaseError.Errorf("failed to delete folder: %w", err)
+			return folder.ErrDatabaseError.Errorf("failed to delete folders: %w", err)
 		}
 		return nil
 	})
@@ -331,6 +340,7 @@ func (ss *sqlStore) getParentsMySQL(ctx context.Context, q folder.GetParentsQuer
 	return util.Reverse(folders), err
 }
 
+// TODO use a single query to get the height of a folder
 func (ss *sqlStore) GetHeight(ctx context.Context, foldrUID string, orgID int64, parentUID *string) (int, error) {
 	height := -1
 	queue := []string{foldrUID}
@@ -460,6 +470,65 @@ func (ss *sqlStore) GetFolders(ctx context.Context, q getFoldersQuery) ([]*folde
 	return folders, nil
 }
 
+func (ss *sqlStore) GetDescendants(ctx context.Context, orgID int64, ancestor_uid string) ([]*folder.Folder, error) {
+	var folders []*folder.Folder
+
+	recursiveQueriesAreSupported, err := ss.db.RecursiveQueriesAreSupported()
+	if err != nil {
+		return nil, err
+	}
+	switch recursiveQueriesAreSupported {
+	case true:
+		recQuery := `
+		WITH RECURSIVE RecQry AS (
+			SELECT * FROM folder WHERE parent_uid = ? AND org_id = ?
+			UNION ALL SELECT f.* FROM folder f INNER JOIN RecQry r ON f.parent_uid = r.uid and f.org_id = r.org_id
+		)
+		SELECT * FROM RecQry;
+	`
+		if err := ss.db.WithDbSession(ctx, func(sess *db.Session) error {
+			err := sess.SQL(recQuery, ancestor_uid, orgID).Find(&folders)
+			if err != nil {
+				return folder.ErrDatabaseError.Errorf("failed to get folder descendants: %w", err)
+			}
+			return nil
+		}); err != nil {
+			return nil, err
+		}
+	default:
+		// this is suboptimal because results is full table scan on f0
+		// but it's the best we can do without recursive CTE
+		if err := ss.db.WithDbSession(ctx, func(sess *db.Session) error {
+			s := strings.Builder{}
+			args := make([]any, 0, 1+folder.MaxNestedFolderDepth)
+			args = append(args, orgID)
+			s.WriteString(`SELECT f0.id, f0.org_id, f0.uid, f0.parent_uid, f0.title, f0.description, f0.created, f0.updated`)
+			s.WriteString(` FROM folder f0`)
+			s.WriteString(getFullpathJoinsSQL())
+			s.WriteString(` WHERE f0.org_id=?`)
+			s.WriteString(` AND (`)
+			for i := 1; i <= folder.MaxNestedFolderDepth; i++ {
+				if i > 1 {
+					s.WriteString(` OR `)
+				}
+				s.WriteString(fmt.Sprintf(`f%d.uid=?`, i))
+				args = append(args, ancestor_uid)
+			}
+			s.WriteString(`)`)
+			return sess.SQL(s.String(), args...).Find(&folders)
+		}); err != nil {
+			return nil, err
+		}
+	}
+
+	// Add URLs
+	for i, f := range folders {
+		folders[i] = f.WithURL()
+	}
+
+	return folders, nil
+}
+
 func getFullpathSQL(dialect migrator.Dialect) string {
 	concatCols := make([]string, 0, folder.MaxNestedFolderDepth)
 	concatCols = append(concatCols, "COALESCE(REPLACE(f0.title, '/', '\\/'), '')")