About trigger

Question

I create four tables in sql 2005 as 

StudentTbl

s_id(PK)	int
s_name	varchar(30)
s_add	varchar(50)

DeptTbl

d_id(PK)	int
d_name	varchar(50)
s_id(FK)	int

STbl_backup

s_id(PK)	int
s_name	varchar(30)
s_add	varchar(50)

DTbl_backup

d_id(PK)	int
d_name	varchar(50)
s_id(FK)	int

and I set StudentTbl cascade with DeptTbl    and  STbl_backup cascade with DTbl_backup.


I write Trigger for Delete on StudentTbl and DeptTbl like this way:


create  trigger  Backup_stbl
on StudentTbl  
for delete 
as 
begin
declare @s_id      int
declare @s_name  varchar(30)
        declare @s_add    varchar(50)

select @s_id=s_id , @s_name=s_name,@s_add=s_add from deleted
insert into STbl_backup values(@s_id,@s_name,@s_add)
end


create  trigger  Backup_dtbl
on DeptTbl  
for delete 
as 
begin
declare @d_id      int
declare @d_name  varchar(30)
        declare @s_id    int

select @d_id=d_id , @d_name=d_name,@s_id=s_id from deleted
insert into DTbl_backup values(@d_id,@d_name,@s_id)
end


Finally I inserted four records .


Expectation of  trigger Backup_stbl  is to get  deleted records of StudentTbl and insert into the STbl_backup table
same is the case for Backup_dtbl.


but when I write following query:



delete from StudentTbl where s_id=2


then It display me error like :


Msg 547, Level 16, State 0, Procedure Backup_dtbl, Line 15
The INSERT statement conflicted with the FOREIGN KEY constraint "FK_DTbl_STbl". The conflict occurred in database "test", table "dbo.STbl", column 's_Id'.
The statement has been terminated.



I Provide You all details If you understand my problem then please suggest me solution. Thanks in advance.