问题
I need to get all the values which changed in a row and post modifications on other 'audit' table. Can I accomplish this, without writing the conditions for each element from the row? I know the SQL from http://www.firebirdfaq.org/faq133/ which gives you all the conditions for verifications:
select 'if (new.' || rdb$field_name || ' is null and old.' ||
rdb$field_name || ' is not null or new.' || rdb$field_name ||
'is not null and old.' || rdb$field_name || ' is null or new.' ||
rdb$field_name || ' <> old.' || rdb$field_name || ') then'
from rdb$relation_fields
where rdb$relation_name = 'EMPLOYEE';
but this should be written in the trigger. So, if I change a table then I need to modify the trigger.
Due the fact that FireBird does not allow dynamically increasing the size of a varchar variable I was thinking of casting and concatenating all the values to a big varchar variable, before inserting it in a text blob.
Is there any possibility to accomplish this, without using GTTs?
回答1:
You need some meta programming, but with triggers on system tables that's no problem.
This solution seems to work, even if you have lots of columns.
set term ^ ;
create or alter procedure create_audit_update_trigger (tablename char(31)) as
declare sql blob sub_type 1;
declare fn char(31);
declare skip decimal(1);
begin
-- TODO add/remove fields to/from audit table
sql = 'create or alter trigger ' || trim(tablename) || '_audit_upd for ' || trim(tablename) || ' after update as begin if (';
skip = 1;
for select rdb$field_name from rdb$relation_fields where rdb$relation_name = :tablename into :fn do
begin
if (skip = 0) then sql = sql || ' or ';
sql = sql || '(old.' || trim(:fn) || ' is distinct from new.' || trim(:fn) || ')';
skip = 0;
end
sql = sql || ') then insert into ' || trim(tablename) || '_audit (';
skip = 1;
for select rdb$field_name from rdb$relation_fields where rdb$relation_name = :tablename into :fn do
begin
if (skip = 0) then sql = sql || ',';
sql = sql || trim(:fn);
skip = 0;
end
sql = sql || ') values (';
skip = 1;
for select rdb$field_name from rdb$relation_fields where rdb$relation_name = :tablename into :fn do
begin
if (skip = 0) then sql = sql || ',';
sql = sql || 'new.' || trim(:fn);
skip = 0;
end
sql = sql || '); end';
execute statement :sql;
end ^
create or alter trigger field_audit for rdb$relation_fields after insert or update or delete as
begin
-- TODO filter table name, don't include system or audit tables
-- TODO add insert trigger
execute procedure create_audit_update_trigger(new.rdb$relation_name);
end ^
set term ; ^
回答2:
This tool is the firebirds solution for your problem:
http://www.upscene.com/products.audit.iblm_main.php
Otherwise You can't access the new./old. variables dynamically.
I investigated an execute statement based solution, but it is also a dead-end.
Using EXECUTE STATEMENT with a context variable (NEW or OLD) will never work, cause that's only available inside a trigger, not in a new statement (the EXECUTE STATEMENT) is not executed inside the trigger, although it uses the same connection and transaction.
来源:https://stackoverflow.com/questions/19157376/firebird-get-all-modified-fields-inside-a-trigger