Instead of trigger in SQL Server loses SCOPE_IDENTITY?

Question

I have a table where I created an INSTEAD OF trigger to enforce some business rules.

The issue is that when I insert data into this table, SCOPE_I

Answer 1

Like araqnid commented, the trigger seems to rollback the transaction when a condition is met. You can do that easier with an AFTER INSTERT trigger:

CREATE TRIGGER [dbo].[TR_Payments_Insert]
   ON  [dbo].[Payment]
   AFTER INSERT
AS 
BEGIN
    SET NOCOUNT ON;

    IF 
    BEGIN
        ROLLBACK TRANSACTION
    END
END

Then you can use SCOPE_IDENTITY() again, because the INSERT is no longer done in the trigger.

The condition itself seems to let two identical rows past, if they're in the same insert. With the AFTER INSERT trigger, you can rewrite the condition like:

IF EXISTS(
    SELECT *
    FROM dbo.Payment a
    LEFT JOIN dbo.Payment b
        ON a.Id <> b.Id
        AND a.CustomerId = b.CustomerId
        AND (a.DateFrom BETWEEN b.DateFrom AND b.DateTo
        OR a.DateTo BETWEEN b.DateFrom AND b.DateTo)
    WHERE b.Id is NOT NULL)

And it will catch duplicate rows, because now it can differentiate them based on Id. It also works if you delete a row and replace it with another row in the same statement.

Anyway, if you want my advice, move away from triggers altogether. As you can see even for this example they are very complex. Do the insert through a stored procedure. They are simpler and faster than triggers:

create procedure dbo.InsertPayment
    @DateFrom datetime, @DateTo datetime, @CustomerId int, @AdminId int
as
BEGIN TRANSACTION

IF NOT EXISTS (
    SELECT *
    FROM dbo.Payment
    WHERE CustomerId = @CustomerId
    AND (@DateFrom BETWEEN DateFrom AND DateTo
    OR @DateTo BETWEEN DateFrom AND DateTo))
    BEGIN

    INSERT into dbo.Payment 
    (DateFrom, DateTo, CustomerId, AdminId)
    VALUES (@DateFrom, @DateTo, @CustomerId, @AdminId)

    END
COMMIT TRANSACTION