Constraint Checks After Insert

Hi all,

I'm trying to use a custom check constraint to insert into a table. I have created a function that checks an item against a authorization date as well and I've coupled this into the constraint. So for example, my function starts:




Code Snippet
ALTER FUNCTION {function1} (@ItemID INT, @AuthDate DATETIME)
RETURNS INT
AS
BEGIN

DECLARE @Ret INT
SET @Ret = 0
IF NOT EXISTS(SELECT top 1 ItemID FROM {table1}
Where b1.ItemID = @ItemID
AND @AuthDate <= ISNULL(b1.expirydate, @AuthDate))
BEGIN
SET @Ret = 1
END
ELSE
BEGIN
SET @Ret = 0
END

RETURN(@Ret)
END
GO



Now i couple that into a check constraint for the same table:




Code Snippet
ALTER TABLE {table1} ADD CONSTRAINT {contraint_name} CHECK (([function1]([ItemID], [AuthorizedDate])=(1)))
GO








Now, when i insert a record into this table with an Authorized Date greater than the ItemDate it should set the @ret value to 1. This is being passed back to the constraint should set 1=1 which is true and therefore should allow an insert, however, i cannot do this. I think this is because it inserts the record and THEN does the check which makes it fail. Is there anyway to do this check before the INSERT without having to use a trigger? I dont want to use a trigger because when we're doing an insert for bulk rows, performance decreases correct?