Re: Statement-level trigger results in recursion

On 2/18/19 8:38 AM, Jitendra Loyal wrote:
> Unfortunately no! Where can I see those? Will I don't my answer there; I
> have referred to the documentation and tried various things.

Please do not top post. The style on this list is to use inline posting.

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 and regards,
> Ken i
>
> On Mon 18 Feb, 2019, 9:59 PM Adrian Klaver, <adrian(dot)klaver(at)aklaver(dot)com
> <mailto:adrian(dot)klaver(at)aklaver(dot)com>> wrote:
>
> On 2/18/19 8:23 AM, Jitendra Loyal wrote:
> > My bad!
> >
> > It is a transition table. Consider the following revised
> definition of
> > trigger:
> >
> >
> > CREATE TRIGGER storage_locations_b_u_AS_DML
> > AFTER UPDATE
> > ON storage_locations
> > REFERENCING NEW TABLE AS new_table
> > OLD TABLE AS old_table
> > FOR EACH STATEMENT EXECUTE FUNCTION
> TRG_storage_locations_b_u_AS_DML ();
>
> Alright I understand now.
>
> Did you see the rest of my previous post about AFTER STATEMENT running
> regardless of number of rows affected?
>
> >
> > Thanks and regards,
> > Jiten
> >
> > On Mon 18 Feb, 2019, 9:32 PM Adrian Klaver,
> <adrian(dot)klaver(at)aklaver(dot)com <mailto:adrian(dot)klaver(at)aklaver(dot)com>
> > <mailto:adrian(dot)klaver(at)aklaver(dot)com
> <mailto:adrian(dot)klaver(at)aklaver(dot)com>>> wrote:
> >
> >     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(dot)klaver(at)aklaver(dot)com <mailto:adrian(dot)klaver(at)aklaver(dot)com>
> <mailto:adrian(dot)klaver(at)aklaver(dot)com <mailto:adrian(dot)klaver(at)aklaver(dot)com>>
> >
>
>
> --
> Adrian Klaver
> adrian(dot)klaver(at)aklaver(dot)com <mailto:adrian(dot)klaver(at)aklaver(dot)com>
>

--
Adrian Klaver
adrian(dot)klaver(at)aklaver(dot)com