Question

I am creating a self-related table:

Table Item columns:
ItemId int – PK;
Amount money – not null;
Price money – a computed column using a UDF that retrieves value according to the items ancestors’ Amount.
ParentItemId int – nullable, reference to another ItemId in this table.

I need to avoid a loop, meaning, a sibling cannot become an ancestor of his ancestors, meaning, if ItemId=2 ParentItemId = 1, then ItemId 1 ParentItemId = 2 shouldn’t be allowed.

I don’t know what should be the best practice in this situation.
I think I should add a CK that gets a Scalar value from a UDF or whatever else.

EDIT:
Another option is to create an INSTEAD OF trigger and put in 1 transaction the update of the ParentItemId field and selecting the Price field from the @@RowIdentity, if it fails cancel transaction, but I would prefer a UDF validating.

Any ideas are sincerely welcomed.

Answer 1

Tested and works just great:

CREATE TRIGGER Item_UPDATE
   ON Item
   FOR INSERT, UPDATE
AS 
BEGIN

BEGIN TRY
    SELECT Price FROM INSERTED
END TRY
BEGIN CATCH
    RAISERROR('This item cannot be specified with this parent.', 16, 1)
    ROLLBACK TRANSACTION;
END CATCH

END
GO