How to write multi-line constraint for ParentId/HierarchyId - sql

Question

I have a table called Items with these three fields:
Id (int)
ParentId(int)
NodeId (HierarchyId)
Id NodeId ParentId
2 / NULL
3 /120/1/ 1520
4 /1/ 2
ParentId and NodeId are basically duplicates as they both point to the parent. In the future, ParentId will be dropped in favor of the HierarchyId.
However, in the meantime, I need to ensure that they stay in sync, so I need to write a constraint to ensure this:
declare #id int = 4
DECLARE #result int = 0, #parentNodeId1 HierarchyId,#parentNodeId2 HierarchyId, #parentId int;
Select #parentNodeId1 = NodeId.GetAncestor(1), #parentId = parentId from Items where id = #id;
Select #parentNodeId2 = NodeId from Items where Id = #parentId;
if #parentNodeId1 = #parentNodeId2
Select #result = 1;
How do I write this as a constraint?
Update
I tried Damiens solution as suggested. It works to enforce the multi-column integrity on existing data. However, the NodeId can change from left to right in the hierarchy. For example a NodeId of /1/ can change to /3/. It's parent has not changed (the parent is /), so really the Foreign Key has not been in-validated. And this works for items with no children.
However, if an item has children, and the NodeId is changed, the database engine sees it as a violation of the Foreign Key and throws an error.
See this DB Fiddle: https://dbfiddle.uk/?rdbms=sqlserver_2017&fiddle=44637c2bbed80b8db3f305933798cdad
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
CREATE TABLE [dbo].[People](
[Id] [int] NOT NULL,
[ParentId] [int] NULL,
[NodeId] [hierarchyid] NOT NULL,
[_ParentNodeId] AS ([NodeId].[GetAncestor]((1))) PERSISTED,
CONSTRAINT [PK_People] PRIMARY KEY CLUSTERED
(
[Id] ASC,
[NodeId] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
) ON [PRIMARY]
GO
INSERT [dbo].[People] ([Id], [ParentId], [NodeId]) VALUES (1, NULL, N'/')
GO
INSERT [dbo].[People] ([Id], [ParentId], [NodeId]) VALUES (2, 1, N'/2/')
GO
INSERT [dbo].[People] ([Id], [ParentId], [NodeId]) VALUES (3, 1, N'/3/')
GO
INSERT [dbo].[People] ([Id], [ParentId], [NodeId]) VALUES (4, 2, N'/2/1/')
GO
INSERT [dbo].[People] ([Id], [ParentId], [NodeId]) VALUES (5, 4, N'/2/1/1.1/')
GO
ALTER TABLE [dbo].[People] WITH CHECK ADD CONSTRAINT [FK_People_Parent] FOREIGN KEY([ParentId], [_ParentNodeId])
REFERENCES [dbo].[People] ([Id], [NodeId])
GO
ALTER TABLE [dbo].[People] CHECK CONSTRAINT [FK_People_Parent]
GO
Update People set NodeId = N'/2/1/2/' where Id = 5--Works
Update People set NodeId = N'/2/2/' where Id = 4 --Error

Answer 1

If we can add another column, a foreign key constraint can enforce this:
create table T(
Id int not null,
NodeId hierarchyid,
ParentId int,
_ParentNodeId as NodeId.GetAncestor(1) persisted,
constraint PK_T primary key (Id,NodeId),
constraint FK_T_Parent foreign key (ParentId,_ParentNodeId) references T (Id,NodeId)
)
(I'm using the PK as the FK target, but any unique constraint will do if, say, Id is the current PK and you want to keep that)
I've prefixed the new column name with _. That's my convention for "I'm adding this column for my purposes in enforcing integrity. I don't expect anybody else to ever even look in it".