Thread: Rules, functions and RETURNING

Hello list,

I am trying to wirte a rule which calls a PLPgSQL-function upon an
Insert in a table. Here is a somewhat simplified example of what i got
so far:

CREATE TABLE mytable (mytable_id serial PRIMARY KEY,something text
);


CREATE OR REPLACE FUNCTION _rule_insert_my(something text) RETURNS integer AS
$BODY$
BEGIN-- do somethingreturn mytable_id;
END;
$BODY$ LANGUAGE 'plpgsql' VOLATILE COST 100;


CREATE OR REPLACE RULE _insert AS   ON INSERT TO mytable DO INSTEAD  SELECT
_rule_insert_my(new.something) AS mytable_id;


So far this works quite well. But I got a few situations where I need to
do a query which uses RETURNING to get the value of the newly generated
primary key. Like this one:

INSERT INTO mytable (something) VALUES ('some text') RETURNING mytable_id;

This breaks because I did not specify a RETURNING-Clause in the rule.
But how can specify RETURNING with SELECT?


Thank your in advance for your help.

regards,
nico

-- 
Nico Mandery

On Thursday 17 September 2009 8:35:52 am Nico Mandery wrote:
> Hello list,
>
> I am trying to wirte a rule which calls a PLPgSQL-function upon an
> Insert in a table. Here is a somewhat simplified example of what i got
> so far:
>
> CREATE TABLE mytable (
>     mytable_id serial PRIMARY KEY,
>     something text
> );
>
>
> CREATE OR REPLACE FUNCTION _rule_insert_my(something text)
>   RETURNS integer AS
> $BODY$
> BEGIN
>     -- do something
>     return mytable_id;
> END;
> $BODY$
>   LANGUAGE 'plpgsql' VOLATILE
>   COST 100;
>
>
> CREATE OR REPLACE RULE _insert AS
>     ON INSERT TO mytable DO INSTEAD  SELECT
> _rule_insert_my(new.something) AS mytable_id;
>
>
> So far this works quite well. But I got a few situations where I need to
> do a query which uses RETURNING to get the value of the newly generated
> primary key. Like this one:
>
> INSERT INTO mytable (something) VALUES ('some text') RETURNING mytable_id;
>
> This breaks because I did not specify a RETURNING-Clause in the rule.
> But how can specify RETURNING with SELECT?
>
>
> Thank your in advance for your help.
>
> regards,
> nico
>
> --
> Nico Mandery

I am going to assume that '--do something' is more complicated then getting the 
mytable_id. If that is the case why not create an INSERT function/trigger that 
does the 'something' and then just do:
INSERT INTO mytable (something) VALUES ('some text') RETURNING mytable_id;

-- 
Adrian Klaver
aklaver@comcast.net

Adrian Klaver wrote:
> On Thursday 17 September 2009 8:35:52 am Nico Mandery wrote:
>> Hello list,
>>
>> I am trying to wirte a rule which calls a PLPgSQL-function upon an
>> Insert in a table. Here is a somewhat simplified example of what i got
>> so far:
>>
>> CREATE TABLE mytable (
>>     mytable_id serial PRIMARY KEY,
>>     something text
>> );
>>
>>
>> CREATE OR REPLACE FUNCTION _rule_insert_my(something text)
>>   RETURNS integer AS
>> $BODY$
>> BEGIN
>>     -- do something
>>     return mytable_id;
>> END;
>> $BODY$
>>   LANGUAGE 'plpgsql' VOLATILE
>>   COST 100;
>>
>>
>> CREATE OR REPLACE RULE _insert AS
>>     ON INSERT TO mytable DO INSTEAD  SELECT
>> _rule_insert_my(new.something) AS mytable_id;
>>
>>
>> So far this works quite well. But I got a few situations where I need to
>> do a query which uses RETURNING to get the value of the newly generated
>> primary key. Like this one:
>>
>> INSERT INTO mytable (something) VALUES ('some text') RETURNING mytable_id;
>>
>> This breaks because I did not specify a RETURNING-Clause in the rule.
>> But how can specify RETURNING with SELECT?
>>
>>
>> Thank your in advance for your help.
>>
>> regards,
>> nico
>>
>> --
>> Nico Mandery
> 
> I am going to assume that '--do something' is more complicated then getting the 
> mytable_id. If that is the case why not create an INSERT function/trigger that 
> does the 'something' and then just do:
> INSERT INTO mytable (something) VALUES ('some text') RETURNING mytable_id;

Adrian,

I just rewrote a few queries to use the function directly instead of an
insert. But a trigger which fires before the actual INSERT or UPDATE is
a good suggestion. In the case I do not want any data to be inserted in
the table, returning NULL from the trigger should  do the trick.

thanks a lot.

regards,
nico