SQL - Using a Trigger to occasionally allow row deletions - sql

Question

I have some views I'm working with, and I need to set up a trigger to prevent the deletion of any data within the view if the data table is locked by a variable in another table. I already have the trigger set up, and have no issue with setting up the replacement of the delete command using an 'INSTEAD OF DELETE' trigger, but my issue now is how to preserve the incoming delete query for the times where deletions are allowed. In this case, I'm using SQL Server.
For example, if the control table says my view is locked, then any delete query sent to the database should be stopped, and an error message should be returned (no problems here, have this already). However, if the control table says my view is unlocked, I need to be able to allow the delete query to delete data from the view (here I need help).
Code:
CREATE TRIGGER [database_name].[trigger_name]
ON [database_name].[view_name]
INSTEAD OF DELETE
AS
BEGIN
SET NOCOUNT ON
IF NOT EXISTS (SELECT * FROM [database_name].[control_table_name]
WHERE Control_Item = 'view_name' AND Can_modify = 'N')
BEGIN
SET NOCOUNT OFF
--NEW DELETION STATEMENT GOES HERE, NEEDS TO BE DUPLICATE OF REPLACED DELETE QUERY--
END
ELSE
BEGIN
RAISEERROR('Deletions are currently disabled!', 11, 1);
END
END
I'm sure there's some stupid logic statement or something I'm missing but I'll appreciate all the help I can get. Thanks!

Answer 1

You cannot delete from the view directly - you need to delete from the underlying table(s).
So basically, you need to add one (or several) DELETE statements for your tables - and hopefully, you've included the primary keys from all the underlying tables into your view!
CREATE TRIGGER [database_name].[trigger_name]
ON [database_name].[view_name]
INSTEAD OF DELETE
AS
BEGIN
SET NOCOUNT ON
IF NOT EXISTS (SELECT * FROM [database_name].[control_table_name]
WHERE Control_Item = 'view_name' AND Can_modify = 'N')
BEGIN
SET NOCOUNT OFF
DELETE FROM dbo.YourFirstTable
WHERE PrimaryKeyColumn IN (SELECT FirstPrimaryKeyColumn FROM Deleted);
-- if the view is built on top of several tables, you possibly need multiple DELETE statements here
DELETE FROM dbo.YourSecondTable
WHERE PrimaryKeyColumn IN (SELECT SecondPrimaryKeyColumn FROM Deleted);
END
ELSE
BEGIN
RAISEERROR('Deletions are currently disabled!', 11, 1);
END
END

Answer 2

Perhaps a 'FOR DELETE' can do the trick, and do a rollback when the delete is not allowed.
CREATE TRIGGER [database_name].[trigger_name]
ON [database_name].[view_name]
FOR DELETE
AS
SET NOCOUNT ON
IF EXISTS (SELECT *
FROM [database_name].[control_table_name]
WHERE Control_Item = 'view_name' AND Can_modify = 'N')
BEGIN
RAISEERROR('Deletions are currently disabled!', 11, 1) WITH NOWAIT
ROLLBACK
END
SET NOCOUNT OFF
GO