T-SQL hierarchy - get breadcrumbs using query - sql-server

Question

I have virtual folder structure saved in database and I want to get the breadcrumbs from the current folder to the root. The data can be unsorted (but better will be sorted) and I want the parent folders of the current folder only.
The table definition is:
DECLARE Folders TABLE (
FOL_PK INT IDENTITY(1,1) NOT NULL,
FOL_Name VARCHAR(200) NOT NULL,
FOL_FOL_FK INT NULL -- Foreign key to parent
)
And this is my solution:
DECLARE #FOL_PK INT = 5 -- Current folder PK
DECLARE #breadcrumbs TABLE (
FOL_PK INT NOT NULL,
FOL_Name VARCHAR(200) NOT NULL,
FOL_FOL_FK INT NULL
)
DECLARE #isRoot BIT = 0
,#currentFolderPK INT
,#parentFK INT
-- Get current and parent folder PK
SELECT
#currentFolderPK = FOL_PK
FROM
Folder
WHERE
FOL_PK = #FOL_PK
-- Breadcrumb
WHILE (#isRoot = 0)
BEGIN
-- Save to breadcrumb
INSERT INTO #breadcrumbs
SELECT
FOL_PK,
FOL_Name,
FOL_FOL_FK
FROM
Folder
WHERE
FOL_PK = #currentFolderPK
-- Set parent as current
SET #currentFolderPK =
(
SELECT
FOL_FOL_FK
FROM
Folder
WHERE
FOL_PK = #currentFolderPK
)
-- Set flag for loop
SET #isRoot = CASE
WHEN ISNULL(#currentFolderPK, 0) = 0 THEN 1
ELSE 0
END
END
-- Return breadcrumbs
SELECT
FOL_PK AS PK,
FOL_Name AS Name,
FOL_FOL_FK AS ParentFK
FROM
#breadcrumbs
The problem is I am not very comfortable with the loop. Is there any other sophisticated solution how to do this?

Answer 1

Try this using a recursive Common Table Expression (CTE):
SQL Fiddle
MS SQL Server 2008 Schema Setup:
CREATE TABLE [Folders](
[FOL_PK] [int] IDENTITY(1,1) NOT NULL,
[FOL_Name] [varchar](200) NOT NULL,
[FOL_FOL_FK] [int] NULL,
CONSTRAINT [PK__Folders__FOL_PK] PRIMARY KEY CLUSTERED
(
[FOL_PK] ASC
))
ALTER TABLE [dbo].[Folders]
WITH CHECK ADD CONSTRAINT [FK_Folders_Folders] FOREIGN KEY([FOL_FOL_FK])
REFERENCES [dbo].[Folders] ([FOL_PK])
ALTER TABLE [dbo].[Folders] CHECK CONSTRAINT [FK_Folders_Folders]
INSERT INTO Folders(FOL_Name, FOL_FOL_FK)
VALUES ('Level 1', NULL),
('Level 1.1', 1),
('Level 1.2', 1),
('Level 1.3', 1),
('Level 1.2.1', 3),
('Level 1.2.2', 3),
('Level 1.2.3', 3),
('Level 1.2.2.1', 6),
('Level 1.2.2.2', 6),
('Level 1.2.2.3', 6),
('Level 1.3.1', 4),
('Level 1.3.2', 4)
Query 1:
DECLARE #FolderId Int = 9
;WITH CTE
AS
(
SELECT FOL_PK AS PK, FOL_NAME As Name, FOL_FOL_FK AS ParentFK
FROM Folders
WHERE FOL_PK = #FolderId
UNION ALL
SELECT F.FOL_PK AS PK, F.FOL_NAME AS Name, F.FOL_FOL_FK AS ParentFK
FROM Folders F
INNER JOIN CTE C
ON C.ParentFK = F.FOL_PK
)
SELECT *
FROM CTE
Results:
| PK | Name | ParentFK |
|----|---------------|----------|
| 9 | Level 1.2.2.2 | 6 |
| 6 | Level 1.2.2 | 3 |
| 3 | Level 1.2 | 1 |
| 1 | Level 1 | (null) |