TSQL variable object reference not set to instance of an object - sql-server

Question

I'm trying to create a trigger that initialises a record over multiple tables when a master record is inserted to a master table. The code below gives the error "Object reference not set to an instance of an object."
Appraisal is the table the trigger exists for and every table concerned has an AppraisalID foreign key.
BEGIN TRANSACTION
DECLARE #appraisalid int
SET #appraisalid = (SELECT AppraisalID FROM inserted)
INSERT INTO dbo.AppraisalCPD (AppraisalID)
VALUES (#appraisalid)
COMMIT;
The code below works, but I would rather use a variable to assign the value as I need to add rows to a fair few tables.
BEGIN
INSERT INTO dbo.AppraisalCPD
(AppraisalID)
SELECT AppraisalID
FROM inserted;
END;
If anyone can suggest a way to set an appraisalid variable using the inserted row in the Appraisal table to insert rows into every other table I need to, that'd be very helpful.

Answer 1

I am assuming you are talking about home appraisal.
The [appraisal] table is the parent and the [owners]/[location] are the children.
Here is a play schema in tempdb.
-- just playing
use tempdb;
go
-- drop table
if object_id('appraisal') > 0
drop table appraisal
go
-- create table - home appraisal
create table appraisal
(
app_id int identity (1,1),
app_request datetime,
app_employee_id int
);
-- drop table
if object_id('owners') > 0
drop table owners
go
-- create table - the owners
create table owners
(
own_id int identity (1,1) primary key,
own_first_nm varchar(64),
own_last_nm varchar(64),
app_id int
);
-- drop table
if object_id('location') > 0
drop table location
go
-- the location
create table location
(
loc_id int identity (1,1) primary key,
loc_street varchar(64),
loc_city varchar(64),
loc_state varchar(2),
loc_zip varchar(9),
app_id int
);
go
When creating empty child records via a trigger, you either have to define default values or supply them in the trigger.
Also, I leave setting up foreign keys for you to handle.
The code for the trigger could look like the following.
-- The trigger
CREATE TRIGGER DBO.make_empty_children on dbo.appraisal
for insert, update, delete
as
BEGIN
-- nothing to do?
IF (##rowcount = 0) RETURN;
-- do not count rows
SET NOCOUNT ON;
-- delete
IF NOT EXISTS (SELECT * FROM inserted)
BEGIN
RETURN;
END
-- insert
ELSE IF NOT EXISTS (SELECT * FROM deleted)
BEGIN
-- dummy record for owners
insert into owners
(
own_first_nm,
own_last_nm,
app_id
)
select
'enter first name',
'enter last name',
app_id
from
inserted;
-- dummy record for location
insert into location
(
loc_street,
loc_city,
loc_state,
loc_zip,
app_id
)
select
'enter street',
'enter city',
'ri',
'00000',
app_id
from
inserted;
RETURN;
END
-- update
ELSE
BEGIN
RETURN;
END
END
GO
I left place holders for DELETE and UPDATE operations.
1 - Do you want to reject updates to the id (key) in the appraisal table. Probably not. This can also be taken care (prevented) of by a Foreign Key (FK).
2 - Do you want to cascade deletes? This also can be handled by a FK or in code in the trigger.
Lets see no records in the tables.
select * from appraisal;
select * from owners;
select * from location;
Like Marc / Aaron said, the inserted / deleted tables are record sets. Not a single row.
Order is not guaranteed. Use an order by if you want the records inserted by app id order.
-- Insert 2 records
insert into appraisal
(
app_request,
app_employee_id
)
values
(getdate(), 7),
(dateadd(d, 1, getdate()), 7);
-- Lets see the data
select * from appraisal;
select * from owners;
select * from location;