PERSISTED Columns with HierarchyId Datatype - SQL Server 2008 by serverku

I think you have already read all the articles related to HierarchyId in the past And hope you understood the concept and usage of it. You also experienced with performance by using HierarchyId datatype as I have posted the performance review in earlier posts as well.

With earlier posts you got some basic methods or functions as how we get the hierarchy data levels, root node, string path. Also, some other methods like as how can we get up-line & down-line modes. Here I am going to present the same, but as Persisted column. So we do not need to write those functions in query level every time. Let us see the workaround for that.

How can ?
We need to create one table and define those columns as a function call as a PERSISTED. We will look the methods to get the hierarchical data without defining columns as Persisted columns and we will use those function calls at the query level. The scripts for the same are as follows.

-- Creating objects
IF (OBJECT_ID('TblHierarchyStructure','U') > 0)
DROP TABLE TblHierarchyStructure
GO

CREATE TABLE TblHierarchyStructure
  (
     ItemId        INT,
     ParentItemId  INT,
     ItemOrder     INT,
     ItemName      VARCHAR(100),
     HierarchyNode HIERARCHYID
  )

GO

-- Inseting records in tables for the demo
INSERT INTO TblHierarchyStructure
            (ItemId,
             ParentItemId,
             ItemOrder,
             ItemName,
             HierarchyNode)
SELECT 1,
       NULL,
       1,
       'RootItem',
       HierarchyId::Parse('/')
UNION ALL
SELECT 2,
       1,
       1,
       'FirstItem',
       HierarchyId::Parse('/1/')
UNION ALL
SELECT 3,
       1,
       2,
       'SecondItem',
       HierarchyId::Parse('/2/')
UNION ALL
SELECT 4,
       1,
       3,
       'ThirdItem',
       HierarchyId::Parse('/3/')
UNION ALL
SELECT 5,
       2,
       1,
       'FourthItem',
       HierarchyId::Parse('/1/1/')
UNION ALL
SELECT 6,
       4,
       1,
       'FifthItem',
       HierarchyId::Parse('/3/1/')
UNION ALL
SELECT 7,
       5,
       1,
       'SixthItem',
       HierarchyId::Parse('/1/1/1/')
UNION ALL
SELECT 8,
       5,
       2,
       'SeventhItem',
       HierarchyId::Parse('/1/1/2/')
UNION ALL
SELECT 9,
       5,
       3,
       'NinthItem',
       HierarchyId::Parse('/1/1/3/')
UNION ALL
SELECT 10,
       8,
       1,
       'TenthItem',
       HierarchyId::Parse('/1/1/2/1/')

GO

-- Usinf HierarchyId functions at query level and see output.
SELECT *,
       HierarchyNode.ToString()                AS ItemNodeString,
       HierarchyNode.GetLevel()                AS ItemNodeLevel,
       HierarchyNode.GetAncestor(1)            AS ParentNode,
       HierarchyNode.GetAncestor(1).ToString() AS ParentNodeString
FROM   TblHierarchyStructure
GO

Now we will look the methods to get the hierarchical data with defining columns as Persisted columns and we will use those functions call at the column level. The scripts for the same are as follows.

-- Creating objects
IF (OBJECT_ID('TblHierarchyStructure','U') > 0)
DROP TABLE TblHierarchyStructure
GO

CREATE TABLE TblHierarchyStructure
  (
     ItemId        INT,
     ParentItemId  INT,
     ItemOrder     INT,
     ItemName      VARCHAR(100),
     HierarchyNode HIERARCHYID NOT NULL PRIMARY KEY,
     ItemNodeString AS HierarchyNode.ToString() PERSISTED,
     ItemNodeLevel AS HierarchyNode.GetLevel() PERSISTED,
     ParentNode AS HierarchyNode.GetAncestor(1) PERSISTED,
     ParentNodeString AS HierarchyNode.GetAncestor(1).ToString()
  )

GO

-- Inserting sample records here 
INSERT INTO TblHierarchyStructure
            (ItemId,
             ParentItemId,
             ItemOrder,
             ItemName,
             HierarchyNode)
SELECT 1,
       NULL,
       1,
       'RootItem',
       HierarchyId::Parse('/')
UNION ALL
SELECT 2,
       1,
       1,
       'FirstItem',
       HierarchyId::Parse('/1/')
UNION ALL
SELECT 3,
       1,
       2,
       'SecondItem',
       HierarchyId::Parse('/2/')
UNION ALL
SELECT 4,
       1,
       3,
       'ThirdItem',
       HierarchyId::Parse('/3/')
UNION ALL
SELECT 5,
       2,
       1,
       'FourthItem',
       HierarchyId::Parse('/1/1/')
UNION ALL
SELECT 6,
       4,
       1,
       'FifthItem',
       HierarchyId::Parse('/3/1/')
UNION ALL
SELECT 7,
       5,
       1,
       'SixthItem',
       HierarchyId::Parse('/1/1/1/')
UNION ALL
SELECT 8,
       5,
       2,
       'SeventhItem',
       HierarchyId::Parse('/1/1/2/')
UNION ALL
SELECT 9,
       5,
       3,
       'NinthItem',
       HierarchyId::Parse('/1/1/3/')
UNION ALL
SELECT 10,
       8,
       1,
       'TenthItem',
       HierarchyId::Parse('/1/1/2/1/')

GO

-- We have not using HierarchyId functions at query level
-- and using them at columns level as Persisted
SELECT 
*
FROM   TblHierarchyStructure 

GO

I hope you liked this post about Persisted columns with HierarchyID new datatype. Share your experience if you know this type of the usage.