trigger for insert or update after checking relationship - sql-server

Question

I have this 3 tables:
And i need to build a trigger that: A date ("encontro") can only works when theres a friendship ("amizade") between 2 profiles ("perfis").
I've created this trigger but i feel lost.. HELP ME
CREATE TRIGGER relaçoes_after_insert
ON encontros
INSTEAD OF insert -
as
begin
declare #idperfilA int;
declare #idperfilB int;
declare #data datetime;
declare #count int;
declare cursor_1 cursor for select * from inserted;
open cursor_1;
fetch next from cursor_1 into #idperfilA, #idperfilB, #data;
WHILE ##FETCH_STATUS = 0
BEGIN
if exists( select * from inserted i, amizade a
where i.IDPERFILA = a.IDPERFILA and i.IDPERFILB = a.IDPERFILB and GETDATE() > DATA)
RAISERROR('there isnt friendship', 16, 10);
else
insert into ENCONTROS select * from inserted;
end;
fetch next from cursor_1 into #idperfilA, #idperfilB, #data;
END
close cursor_1;
deallocate cursor_1;

Answer 1

I think the better answer would be to not create use a trigger for this at all. Instead I would create and enforce a foreign key constraint between encontros and amizade.
As far as I can tell, this will result in doing what you want without having to write your own code to try and recreate behavior provided by the database. It also makes it much easier to understand from a database design point of view.
alter table dbo.encontros
add constraint fk_amizade__encontros
foreign key (idperflia, idperflib) references dbo.amizade (idperflia, idperflib)
/* optional
on delete { no action | cascade | set null | set default } -- pick one, usual defualt is: no action
on update { no action | cascade | set null | set default } -- pick one, usual defualt is: no action
--*/*
;
More about table constraints.
NO ACTION
The SQL Server Database Engine raises an error and the delete action on the row in the parent table is rolled back.
CASCADE
Corresponding rows are deleted from the referencing table if that row is deleted from the parent table.
SET NULL
All the values that make up the foreign key are set to NULL when the corresponding row in the parent table is deleted. For this constraint to execute, the foreign key columns must be nullable.
SET DEFAULT
All the values that comprise the foreign key are set to their default values when the corresponding row in the parent table is deleted. For this constraint to execute, all foreign key columns must have default definitions. If a column is nullable and there is no explicit default value set, NULL becomes the implicit default value of the column.
Based on your reply to #3N1GM4:
#3N1GM4 if exists some friendship with a date after today (for example) it is an error, so the friendship doesnt exist. But i dont know if it matters at this point. IDPERFILA and IDPERFILB will match A and B at amizade table, but i need to make sure that they were not the same
You could create a check constraint on amizade that will prevent rows with invalid dates from being inserted into the table.
alter table dbo.amizade
add constraint chk_data_lt_getdate ([data] < get_date());
More about check constraints; more examples from Gregory Larson.
original answer:
I'm still waiting on some clarification on the question, but one of the versions in this should be on the right path:
create trigger relaçoes_after_insert
on encontros
instead of insert
as
begin
/* To abort when any row doesn't have a matching friendship */
if not exists (
select 1
from inserted i
where exists (
select 1
from amizade a
where a.idperfila = i.idperfila
and a.idperfilb = i.idperfilb
and getdate() > data /* not sure what this part does */
/* as #3N1GM4 pointed out,
if the position doesn't matter between idperflia and idperflib then:
where (i.idperfila = a.idperfila and i.idperfilb = a.idperfilb)
or (i.idperfila = a.idperfilb and i.idperfilb = a.idperfila)
*/
)
begin;
raiserror('there isnt friendship', 16, 10);
else
insert into encontros
select * from inserted;
end;
end;
/* To insert all rows that have a matching friendship, you could use this instead */
insert into encontros
select i.*
from inserted i
where exists (
select 1
from amizade a
where a.idperfila = i.idperfila
and a.idperfilb = i.idperfilb
and getdate() > data /* not sure what this part does */
/* as #3N1GM4 pointed out,
if the position doesn't matter between idperflia and idperflib then:
where (i.idperfila = a.idperfila and i.idperfilb = a.idperfilb)
or (i.idperfila = a.idperfilb and i.idperfilb = a.idperfila)
*/
)
end;
The only potential issue I see with using an inner join instead of exists for the second option (inserting rows that have a friendship and ignoring ones that don't) is if there could ever be an issue where (i.idperfila = a.idperfila and i.idperfilb = a.idperfilb) or (i.idperfila = a.idperfilb and i.idperfilb = a.idperfila) would return duplicates of the inserted rows from each condition returning a match.