Introducing FOREIGN KEY constraint may cause cycles or multiple cascade paths - sql

Question

I have this sql script to create database in mssql:
CREATE TABLE ENTITY (
ID bigint IDENTITY(1,1) NOT NULL,
NAME nvarchar(255) NOT NULL,
PARENT_ID bigint NULL
)
go
ALTER TABLE ENTITY
ADD CONSTRAINT PK_ENTITY PRIMARY KEY CLUSTERED (ID)
WITH FILLFACTOR = 80
go
ALTER TABLE ENTITY
ADD CONSTRAINT FK_ENTITY FOREIGN KEY (PARENT_ID)
REFERENCES ENTITY (ID) ON DELETE CASCADE ON UPDATE CASCADE
go
By design i'd like to create parent->child relations in single table
So, just some pseudocode examples:
id | name | parent_id
1 Mother null
2 Steve 1
3 Jack 1
I'd like to remove Mother with all DELETE Cascade childs if needed
But after i install this script i receive:
Introducing FOREIGN KEY constraint 'FK_ENTITY' on table 'ENTITY' may cause cycles or multiple cascade paths. Specify ON DELETE NO ACTION or ON UPDATE NO ACTION, or modify other FOREIGN KEY constraints.
Is any solution how i can implement such single table hierarchy correctly?

Answer 1

It seems sql server doesn't let Cascading DELETE with Recursive Foreign Keys, so you can write procedure for your delete action like below :
CREATE PROC DeleteChildWithParent(#ID BIGINT)
AS
;WITH ChildToDelete AS (
SELECT id, CAST(1 AS INT) AS ChildLevel
FROM ENTITY
WHERE id = #ID
UNION ALL
SELECT e.id, C.ChildLevel + 1
FROM ENTITY E
JOIN ChildToDelete C ON e.PARENT_ID = C.ID AND E.PARENT_ID <> E.ID
)
SELECT id, ROW_NUMBER() OVER (ORDER BY ChildLevel DESC) Ord
INTO #ChildToDelete
FROM ChildToDelete
DECLARE #count INT = 1, #max INT = ##ROWCOUNT;
WHILE #count <= #max
BEGIN
DELETE ENTITY WHERE id = (SELECT id FROM #ChildToDelete WHERE Ord = #count);
SET #count = #count + 1;
END;
GO