On 2/18/19 4:11 AM, Jitendra Loyal wrote:
The AFTER Statement-level Trigger runs into infinite execution when
another set of rows are affected for the same table through this
trigger. Consider this use case where a table storage_locations that
manages a hierarchy of storage_locations in stores, and thus having
following columns (for simplicity):
storage_location_id SERIAL NOT NULL PRIMARY KEY,
store_id INTEGER NOT NULL, -- REFERENCES stores
storage_location_nm VARCHAR (25) NOT NULL,
parent_storage_location_id INTEGER NULL REFERENCES storage_locations,
---- NULL for root storage locations
storage_location_path TEXT NOT NULL
I have a BEFORE ROW trigger, which updates the storage_location_path with
parent's storage_location_path, if any, concatenated with its
storage_location_name. This works fine - no issues.
I have another AFTER UPDATE STATEMENT-level Trigger and function definitions
as below (which updates the storage_path of the children):
CREATE FUNCTION TRG_storage_locations_b_u_AS_DML ()
RETURNS TRIGGER
AS $$
DECLARE
v_separator VARCHAR (1) = '/';
v_cnt INT;
BEGIN
-- [ -- Required to prevent infinite recursion
SELECT COUNT (*) INTO v_cnt
FROM new_table;
Where is new_table coming from?
IF (v_cnt > 0) THEN
-- ] -- Required to prevent infinite recursion
UPDATE storage_locations
SET storage_location_path = COALESCE (i.storage_location_path ||
v_separator, '') || storage_locations.storage_location_nm
FROM inserted i
JOIN deleted d
ON ( i.storage_location_id = d.storage_location_id
AND i.storage_location_path != d.storage_location_path
)
WHERE storage_locations.parent_storage_location_id = i.storage_location_id;
END IF;
RETURN NULL;
END
$$ LANGUAGE plpgsql;
CREATE TRIGGER storage_locations_b_u_AS_DML
AFTER UPDATE
ON storage_locations
REFERENCING NEW TABLE AS inserted
OLD TABLE AS deleted
FOR EACH STATEMENT EXECUTE FUNCTION TRG_storage_locations_b_u_AS_DML ();
Notice that the Trigger is getting called endlessly (if the number of
rows in the NEW TABLE are NOT checked). I reckon if there are not any
rows, what is the need to call the trigger. Or, may be, I am missing
something, which I need to learn.
Yes:
https://www.postgresql.org/docs/10/sql-createtrigger.html
"... In contrast, a trigger that is marked FOR EACH STATEMENT only
executes once for any given operation, regardless of how many rows it
modifies (in particular, an operation that modifies zero rows will still
result in the execution of any applicable FOR EACH STATEMENT triggers)."
Thanks,
Jiten
--
Adrian Klaver
adrian.klaver@xxxxxxxxxxx
