Statement-level trigger results in recursion

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@aklaver.com

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 ();

Thanks and regards,
Jiten

On Mon 18 Feb, 2019, 9:32 PM Adrian Klaver, <adrian.klaver@aklaver.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.klaver@aklaver.com
<mailto:adrian.klaver@aklaver.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.klaver@aklaver.com <mailto:adrian.klaver@aklaver.com>

--
Adrian Klaver
adrian.klaver@aklaver.com

Unfortunately no! Where can I see those? Will I don't my answer there; I
have referred to the documentation and tried various things.

Thanks and regards,
Ken i

On Mon 18 Feb, 2019, 9:59 PM Adrian Klaver, <adrian.klaver@aklaver.com>
wrote:

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.klaver@aklaver.com
<mailto:adrian.klaver@aklaver.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.klaver@aklaver.com <mailto:adrian.klaver@aklaver.com>

<mailto:adrian.klaver@aklaver.com

<mailto:adrian.klaver@aklaver.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.klaver@aklaver.com <mailto:adrian.klaver@aklaver.com>

<mailto:adrian.klaver@aklaver.com <mailto:adrian.klaver@aklaver.com>>

--
Adrian Klaver
adrian.klaver@aklaver.com <mailto:adrian.klaver@aklaver.com>

--
Adrian Klaver
adrian.klaver@aklaver.com

I do understand that the statement level trigger will be executed once
before the operation. My point is.. if one does not know the rows, what
kind of use it can be put to. What is the use case? Like in after triggers,
one gets the rows in transition tables, how does one do with vefore trigger.

Thanks and regards,
Jiten

On 2/18/19 9:07 AM, Jitendra Loyal wrote:

I do understand that the statement level trigger will be executed once
before the operation. My point is.. if one does not know the rows, what
kind of use it can be put to. What is the use case? Like in after
triggers, one gets the rows in transition tables, how does one do with
vefore trigger.

Use FOR EACH ROW.

Why you cannot use a FOR EACH STATEMENT trigger is something I thought I
remember being discussed on the list before. Unfortunately I cannot find
that conversation at the moment. Someone else will need to weigh in on this.

Thanks and regards,
Jiten

--
Adrian Klaver
adrian.klaver@aklaver.com

Thanks for all your efforts. I appreciate it.

Let us wait and see if someone can enlighten us, or you locate the
conversation.

Thanks once again

Regards,
Jiten

On Tue 19 Feb, 2019, 3:19 AM Adrian Klaver, <adrian.klaver@aklaver.com>
wrote: