Hi I'm up to develop a simple audit trigger for postgresql server. According to this document, I pretty much understand how it works. But I want to record my activity only when the certain row is updated. Below is the code from the link. And it records when there is update no matter what row is updated.
IF (TG_OP = 'UPDATE') THEN
...
Please help me how to give a condition to above code. Thanks!
The trigger is written in PL/PgSQL. I strongly suggest you study the PL/PgSQL manual if you're going to modify PL/PgSQL code.
In triggers, the row data is in OLD and NEW (for UPDATE triggers). So you can do IF tests on that like anything else. E.g.:
IF (TG_OP = 'UPDATE') THEN
IF NEW."name" = 'name_to_audit' OR OLD."name" = 'name_to_audit' THEN
-- do audit commands
END IF;
END IF;
Both NEW and OLD are tested in case the name is being changed from/to the name of interest.
In this case you could instead change it to use a WHEN clause on the CREATE TRIGGER, so you never fire the trigger at all unless the conditions to audit are met. See the WHEN clause on triggers.
This is just a basic programming problem; you'll need to learn the programming language in order to use it.
See also the updated trigger for Pg 9.1.
Oh, and remember to think about NULL; remember NULL = 'anything' is NULL. Use IS DISTINCT FROM if you want to say "these things are equal, or are both null".
From Postgresql Docs:
CREATE TRIGGER log_update
AFTER UPDATE ON accounts
FOR EACH ROW
WHEN (OLD.* IS DISTINCT FROM NEW.*)
EXECUTE PROCEDURE log_account_update();
This only work for UPDATE on that table. For INSERT AND DELETE you can use same without WHERE query. Hope this help others.
Related
i want an upsert functionality that returns the (new/existing) id of the row.
Linking to my previous question. I asked previously about RULE postgres create rule on insert do nothing if exists insert otherwise; RETURNING id but looks like it is not possible.
So I resort to a trigger
CREATE OR REPLACE FUNCTION upsert_asset() RETURNS trigger AS $trigger_bound$
BEGIN
INSERT INTO asset(symbol, name, type, status)
VALUES (NEW.symbol, NEW.name, NEW.type, NEW.status)
ON CONFLICT (symbol) DO UPDATE SET symbol = EXCLUDED.symbol;
RETURN NEW;
END;
$trigger_bound$
LANGUAGE plpgsql;
CREATE OR REPLACE TRIGGER upsert_asset_trigger
AFTER INSERT ON asset
FOR EACH ROW
EXECUTE PROCEDURE upsert_asset();
I tested the above and works. So my questions are
Is this trigger a correct way to achieve this functionality? Any race conditions/performance issues that i should know about?
How can I generalize this query, by not giving the column names? asset(symbol, name, type, status). i do not want to pay attention to this rule every time I change my table. Is it possible to say NEW.* or column.* or something? What psuedorelations are available to achieve this? Please note there are some default columns too. So how does NEW.default_column get a value incase the insert statement has left that column in the insert statement?
Thanks,
So I am working on adding a last updated time to the database for my app's server. The idea is that it will record the time an update is applied to one of our trips and then the app can send a get request to figure out if it's got all of the correct up to date information.
I've added the column to our table, and provided the service for it all, and finally manage to get a trigger going to update the column every time a change is made to a trip in it's trip table. My problem now comes from the fact that the information that pertains to a trip is stored across a multitude of other tables as well (for instance, there are tables for the routes that make up a trip and the photos that a user can see on the trip, etc...) and if any of that data changes, then the trip's update time also needs to change. I can't for the life of me figure out how to set up the trigger so that when I change some route information, the last updated time for the trip(s) the route belongs to will be updated in it's table.
This is my trigger code as it stands now: it updates the trip table's last updated column when that trip's row is updated.
CREATE OR REPLACE FUNCTION record_update_time() RETURNS TRIGGER AS
$$
BEGIN
NEW.last_updated=now();
RETURN NEW;
END;
$$
LANGUAGE PLPGSQL;
CREATE TRIGGER update_entry_on_entry_change
BEFORE UPDATE ON mydatabase.trip FOR EACH ROW
EXECUTE PROCEDURE record_update_time();
--I used the next two queries just to test that the trigger works. It
--probably doesn't make a difference to you but I'll keep it here for reference
UPDATE mydatabase.trip
SET title='Sample New Title'
WHERE id = 2;
SELECT *
FROM mydatabase.trip
WHERE mydatabase.trip.id < 5;
Now I need it to update when the rows referencing the trip row with a foreign key get updated. Any ideas from someone more experienced with SQL triggers than I?
"mydatabase" is a remarkably unfortunate name for a schema.
The trigger function could look like this:
CREATE OR REPLACE FUNCTION trg_upaft_upd_trip()
RETURNS trigger
LANGUAGE plpgsql AS
$func$
BEGIN
UPDATE mydatabase.trip t -- "mydatabase" = schema name (?!)
SET last_updated = now()
WHERE t.id = NEW.trip_id -- guessing column names
RETURN NULL; -- calling this AFTER UPDATE
END
$func$;
And needs to be used in a trigger on every related table (not on trip itself):
CREATE TRIGGER upaft_upd_trip
AFTER UPDATE ON mydatabase.trip_detail
FOR EACH ROW EXECUTE PROCEDURE trg_upaft_upd_trip();
You also need to cover INSERT and DELETE (and possibly COPY) on all sub-tables ...
This approach has many potential points of failure. As alternative, consider a query or view that computes the latest last_updated from sub-tables dynamically. If you update often this might be the superior approach.
If you rarely UPDATE and SELECT often, your first approach might pay.
I created 5 triggers in my small (2 table database).
After I added the last one (to change INVPOS.INVSYMBOL after INVOICE.SYMBOL has been updated) these triggers activated each other and I got a
Too many concurrent executions of the same request.
error.
Could you please look at the triggers I created and help me out?
What can I do to avoid these problems in future? Should I merge a few triggers into one?
One solution could be to check has the intresting field(s) changed and only run the trigger's action if really nessesary (data has changed), ie
CREATE TRIGGER Foo FOR T
AS
BEGIN
-- only execute update statement when the Fld changed
if(new.Fld is distinct from old.Fld)then begin
update ...
end
END
Another option could be to check has the trigger already done it's thing in this transaction, ie
CREATE TRIGGER Foo FOR T
AS
DECLARE trgrDone VARCHAR(255);
BEGIN
trgrDone = RDB$GET_CONTEXT('USER_TRANSACTION', 'Foo');
IF(trgrDone IS NULL)THEN BEGIN
-- trigger hasn't been executed yet
-- register the execution
rdb$set_context('USER_TRANSACTION', 'Foo', 1);
-- do the work which might cause reentry
update ...
END
END
You should avoid circular references between triggers.
In general, triggers are not suitable for complex business logic, they work good for simple "if-then" business rules.
For the case you described you'd better implemenent a stored procedure where you could prepare data for all tables (perform data check, calculate necessary values, etc) and then insert them. It will lead to straightforward, fast and easy-to-maintain code.
Also, use CHECK for "preventing from inserting 0 to AMOUNT and PRICENET", and calculated fields for tasks like "calculate NETVAL".
So, I think this should be fairly simple, but the documentation makes it seem somewhat more complicated. I've written an SQL function in PostgreSQL (8.1, for now) which does some cleanup on some string input. For what it's worth, the string is an LDAP distinguished name, and I want there to consistently be no spaces after the commas - and the function is clean_dn(), which returns the cleaned DN. I want to do the same thing to force all input to another couple of columns to lower case, etc - which should be easy once I figure this part out.
Anyway, I want this function to be run on the "dn" column of a table any time anyone attempts to insert to or update and modify that column. But all the rule examples I can find seem to make the assumption that all insert/update queries modify all the columns in a table all the time. In my situation, that is not the case. What I think I really want is a constraint which just changes the value rather than returning true or false, but that doesn't seem to make sense with the SQL idea of a constraint. Do I have my rule do an UPDATE into the NEW table? Do I have to create a new rule for every possible combination of NEW values? And if I add a column, do I have to go through and update all of my rule combinations to refelect every possible new combination of columns?
There has to be an easy way...
First, update to a current version of PostgreSQL. 8.1 is long dead and forgotten und unsupported and very, very old .. you get my point? Current version is PostgreSQL 9.2.
Then, use a trigger instead of a rule. It's simpler. It's the way most people go. I do.
For column col in table tbl ...
First, create a trigger function:
CREATE OR REPLACE FUNCTION trg_tbl_insupbef()
RETURNS trigger AS
$BODY$
BEGIN
NEW.col := f_myfunc(NEW.col); -- your function here, must return matching type
RETURN NEW;
END;
$BODY$
LANGUAGE plpgsql VOLATILE;
Then use it in a trigger.
For ancient Postgres 8.1:
CREATE TRIGGER insupbef
BEFORE INSERT OR UPDATE
ON tbl
FOR EACH ROW
EXECUTE PROCEDURE trg_tbl_insupbef();
For modern day Postgres (9.0+)
CREATE TRIGGER insbef
BEFORE INSERT OR UPDATE OF col -- only call trigger, if column was updated
ON tbl
FOR EACH ROW
EXECUTE PROCEDURE trg_tbl_insupbef();
You could pack more stuff into one trigger, but then you can't condition the UPDATE trigger on just the one column ...
I have a trigger function for a table test which has the following code snippet:
IF TG_OP='UPDATE' THEN
IF OLD.locked > 0 AND
( OLD.org_id <> NEW.org_id OR
OLD.document_code <> NEW.document_code OR
-- other columns ...
)
THEN
RAISE EXCEPTION 'Message';
-- more code
So I am statically checking all the column's new value with its previous value to ensure integrity. Now every time my business logic changes and I have to add new columns into that table, I will have to modify this trigger each time. I thought it would be better if somehow I could dynamically check all the columns of that table, without explicitly typing their name.
How can it be done?
From 9.0 beta2 documentation about WHEN clause in triggers, which might be able to be used in earlier versions within the trigger body:
OLD.* IS DISTINCT FROM NEW.*
or possibly (from 8.2 release notes)
IF row(new.*) IS DISTINCT FROM row(old.*)
Take a look at the information_schema, there is a view "columns". Execute a query to get all current columnnames from the table that fired the trigger:
SELECT
column_name
FROM
information_schema.columns
WHERE
table_schema = TG_TABLE_SCHEMA
AND
table_name = TG_TABLE_NAME;
Loop through the result and there you go!
More information can be found in the fine manual.
In Postgres 9.0 or later add a WHEN clause to your trigger definition (CREATE TRIGGER statement):
CREATE TRIGGER foo
BEFORE UPDATE
FOR EACH ROW
WHEN (OLD IS DISTINCT FROM NEW) -- parentheses required!
EXECUTE PROCEDURE ...;
Only possible for triggers BEFORE / AFTER UPDATE, where both OLD and NEW are defined. You'd get an exception trying to use this WHEN clause with INSERT or DELETE triggers.
And radically simplify the trigger function accordingly:
...
IF OLD.locked > 0 THEN
RAISE EXCEPTION 'Message';
END IF;
...
No need to test IF TG_OP='UPDATE' ... since this trigger only works for UPDATE anyway.
Or move that condition in the WHEN clause, too:
CREATE TRIGGER foo
BEFORE UPDATE
FOR EACH ROW
WHEN (OLD.locked > 0
AND OLD IS DISTINCT FROM NEW)
EXECUTE PROCEDURE ...;
Leaving only an unconditional RAISE EXCEPTION in your trigger function, which is only called when needed to begin with.
Read the fine print:
In a BEFORE trigger, the WHEN condition is evaluated just before the
function is or would be executed, so using WHEN is not materially
different from testing the same condition at the beginning of the
trigger function. Note in particular that the NEW row seen by the
condition is the current value, as possibly modified by earlier
triggers. Also, a BEFORE trigger's WHEN condition is not allowed to
examine the system columns of the NEW row (such as oid), because those
won't have been set yet.
In an AFTER trigger, the WHEN condition is evaluated just after the
row update occurs, and it determines whether an event is queued to
fire the trigger at the end of statement. So when an AFTER trigger's
WHEN condition does not return true, it is not necessary to queue an
event nor to re-fetch the row at end of statement. This can result in
significant speedups in statements that modify many rows, if the
trigger only needs to be fired for a few of the rows.
Related:
Fire trigger on update of columnA or ColumnB or ColumnC
To also address the question title
Is it possible to dynamically loop through a table's columns?
Yes. Examples:
Handle result when dynamic SQL is in a loop
Removing all columns with given name
Iteration over RECORD variable inside trigger
Use pl/perl or pl/python. They are much better suited for such tasks. much better.
You can also install hstore-new, and use it's row->hstore semantics, but that's definitely not a good idea when using normal datatypes.