Thread: [Trigger] Help needed with NEW.* and TG_TABLE_NAME

[Trigger] Help needed with NEW.* and TG_TABLE_NAME

From

Torsten Zühlsdorff

Date:

11 May 2010, 12:42:35

Hello,

i have a problem with a trigger written in pl/pgsql.

It looks like this:

CREATE OR REPLACE FUNCTION versionize()
RETURNS TRIGGER
AS $$
BEGIN
  NEW.revision := addContentRevision (OLD.content_id, OLD.revision);
  /* not working line, just a stub:  EXECUTE 'INSERT INTO ' || TG_TABLE_NAME  || ' SELECT $1 ' USING NEW;  */
  RETURN NULL;

END;
$$ LANGUAGE 'plpgsql' VOLATILE;

The function should be used at different tables and is invoked before
UPDATEs. Everything what happens is the function call of
addContentRevision. After this call all data (with the updated revision
column) should be stored in the table as a new row.

My problem: the aim-table is not static. It's just always the table
which invoked the trigger. The trigger itself could be called at many
tables. I've tried some other ways of expressing the INSERT but nothing
worked:
- 'INSERT INTO ' || TG_TABLE_NAME  || ' SELECT NEW.*'
- INSERT INTO TG_TABLE_NAME SELECT NEW.*
- EXECUTE 'INSERT INTO ' || TG_TABLE_NAME  USING NEW;

Do you have any hints?

Greetings from Germany,
Torsten


-- 
http://www.dddbl.de - ein Datenbank-Layer, der die Arbeit mit 8 
verschiedenen Datenbanksystemen abstrahiert,
Queries von Applikationen trennt und automatisch die Query-Ergebnisse 
auswerten kann.

Re: [Trigger] Help needed with NEW.* and TG_TABLE_NAME

From

Tom Lane

Date:

11 May 2010, 14:23:47

Torsten Zühlsdorff <foo@meisterderspiele.de> writes:
>    NEW.revision := addContentRevision (OLD.content_id, OLD.revision);

>    /* not working line, just a stub:
>    EXECUTE 'INSERT INTO ' || TG_TABLE_NAME  || ' SELECT $1 ' USING NEW;
>    */

>    RETURN NULL;

This seems like the hard way.  Why don't you just RETURN NEW and let the
normal insertion happen?
        regards, tom lane

Re: [Trigger] Help needed with NEW.* and TG_TABLE_NAME

From

Torsten Zühlsdorff

Date:

11 May 2010, 14:48:47


Tom Lane schrieb:
> Torsten Zühlsdorff <foo@meisterderspiele.de> writes:
>>    NEW.revision := addContentRevision (OLD.content_id, OLD.revision);
> 
>>    /* not working line, just a stub:
>>    EXECUTE 'INSERT INTO ' || TG_TABLE_NAME  || ' SELECT $1 ' USING NEW;
>>    */
> 
>>    RETURN NULL;
> 
> This seems like the hard way.  Why don't you just RETURN NEW and let the
> normal insertion happen?

The trigger catches an UPDATE, not an INSERT. I need the old and the new 
row, because this should emulate revision-control of the content.

Greetings,
Torsten

Re: [Trigger] Help needed with NEW.* and TG_TABLE_NAME

From

silly sad

Date:

12 May 2010, 06:01:07

On 05/11/10 18:26, Torsten Zühlsdorff wrote:
>
>
> Tom Lane schrieb:
>> Torsten Zühlsdorff <foo@meisterderspiele.de> writes:
>>> NEW.revision := addContentRevision (OLD.content_id, OLD.revision);
>>
>>> /* not working line, just a stub:
>>> EXECUTE 'INSERT INTO ' || TG_TABLE_NAME || ' SELECT $1 ' USING NEW;
>>> */
>>
>>> RETURN NULL;
>>
>> This seems like the hard way. Why don't you just RETURN NEW and let the
>> normal insertion happen?
>
> The trigger catches an UPDATE, not an INSERT. I need the old and the new
> row, because this should emulate revision-control of the content.

just set whatever value u want to the fields of the row NEW.

Re: [Trigger] Help needed with NEW.* and TG_TABLE_NAME

From

Jasen Betts

Date:

13 May 2010, 10:51:47

On 2010-05-11, Torsten Zühlsdorff <foo@meisterderspiele.de> wrote:
> Hello,
>
> i have a problem with a trigger written in pl/pgsql.
>
> It looks like this:
>
> CREATE OR REPLACE FUNCTION versionize()
> RETURNS TRIGGER
> AS $$
> BEGIN
>
>    NEW.revision := addContentRevision (OLD.content_id, OLD.revision);
>
>    /* not working line, just a stub:
>    EXECUTE 'INSERT INTO ' || TG_TABLE_NAME  || ' SELECT $1 ' USING NEW;
>    */
>
>    RETURN NULL;
>
> END;
> $$ LANGUAGE 'plpgsql' VOLATILE;
>
> The function should be used at different tables and is invoked before
> UPDATEs. Everything what happens is the function call of
> addContentRevision. After this call all data (with the updated revision
> column) should be stored in the table as a new row.

What many people have missed is that you want to INSERT when the DML
comnabd UPDATE is used.

for things like that usually a rule is used instead, but I can see where
that may be unsuitable for your needs.  I found the following 
to work on a simple test case.

The problem is that INSERT in PLPGSQL needs a fixed table-name, and
that "EXECUTE" can't use variable-names, and further that quote_literal
doesn't convert ROW variables into something that can be used in a
VALUES clause.

so, Here's what I did.
CREATE OR REPLACE FUNCTION versionize()RETURNS TRIGGERAS $$BEGIN
   -- Not havign a definition for addContentRevision   -- I had this line commented out during testing.   NEW.revision
:=addContentRevision (OLD.content_id, OLD.revision);      EXECUTE 'INSERT INTO '||TG_TABLE_NAME||' SELECT (' ||
QUOTE_LITERAL(NEW)|| '::' || TG_TABLE_NAME ||').*' ;

   RETURN NULL;
END;$$ LANGUAGE PLPGSQL VOLATILE;

I take NEW, convert it to a quoted literal so I can use it in EXECUTE, cast it 
to the apreopreiate row type and split it into columns using SELECT
and .*. That gets inserted.

you should probably use QUOTE_IDENT on the TG_TABLE_NAME and possibly
also use similarly quoted TG_SCHEMA_NAME

Re: [Trigger] Help needed with NEW.* and TG_TABLE_NAME

From

Torsten Zühlsdorff

Date:

17 May 2010, 09:20:54

Jasen Betts schrieb:

> On 2010-05-11, Torsten Zühlsdorff <foo@meisterderspiele.de> wrote:
>> Hello,
>>
>> i have a problem with a trigger written in pl/pgsql.
>>
>> It looks like this:
>>
>> CREATE OR REPLACE FUNCTION versionize()
>> RETURNS TRIGGER
>> AS $$
>> BEGIN
>>
>>    NEW.revision := addContentRevision (OLD.content_id, OLD.revision);
>>
>>    /* not working line, just a stub:
>>    EXECUTE 'INSERT INTO ' || TG_TABLE_NAME  || ' SELECT $1 ' USING NEW;
>>    */
>>
>>    RETURN NULL;
>>
>> END;
>> $$ LANGUAGE 'plpgsql' VOLATILE;
>>
>> The function should be used at different tables and is invoked before
>> UPDATEs. Everything what happens is the function call of
>> addContentRevision. After this call all data (with the updated revision
>> column) should be stored in the table as a new row.
> 
> What many people have missed is that you want to INSERT when the DML
> comnabd UPDATE is used.
> 
> for things like that usually a rule is used instead, but I can see where
> that may be unsuitable for your needs.  I found the following 
> to work on a simple test case.
> 
> 
> The problem is that INSERT in PLPGSQL needs a fixed table-name, and
> that "EXECUTE" can't use variable-names, and further that quote_literal
> doesn't convert ROW variables into something that can be used in a
> VALUES clause.
> 
> so, Here's what I did.
> 
>  CREATE OR REPLACE FUNCTION versionize()
>  RETURNS TRIGGER
>  AS $$
>  BEGIN
> 
>     -- Not havign a definition for addContentRevision
>     -- I had this line commented out during testing.
>     NEW.revision := addContentRevision (OLD.content_id, OLD.revision);
>     
>     EXECUTE 'INSERT INTO '||TG_TABLE_NAME||' SELECT (' || 
>        QUOTE_LITERAL(NEW) || '::' || TG_TABLE_NAME ||').*' ;
> 
>     RETURN NULL;
> 
>  END;
>  $$ LANGUAGE PLPGSQL VOLATILE;
> 
> I take NEW, convert it to a quoted literal so I can use it in EXECUTE, cast it 
> to the apreopreiate row type and split it into columns using SELECT
> and .*. That gets inserted.
> 
> you should probably use QUOTE_IDENT on the TG_TABLE_NAME and possibly
> also use similarly quoted TG_SCHEMA_NAME 

That's an quite interesting solution. I've tested it in several ways and 
it works like i want. :)

Thank you very much - and every other responder - for your time.

Greetings from Germany,
Torsten


-- 
http://www.dddbl.de - ein Datenbank-Layer, der die Arbeit mit 8 
verschiedenen Datenbanksystemen abstrahiert,
Queries von Applikationen trennt und automatisch die Query-Ergebnisse 
auswerten kann.