How to get value of $1 parameter from executed prepared statement (inside a trigger using a current_query())

Question

In a trigger I want to see what sql query triggered this trigger. I used current_query() function of postgresql (8.4).

Everything is fine, but if trigger is executed by prepared statement I get placeholders ($1) instead of correct values. for example (logged query):

delete from some_table where id=$1

Is there a way to get/have this values/parameters?

Edited (example added):

--table for saving query
create table log_table (
query text
)

--table for trigger
create table some_table (
id text
)
--function itself
CREATE FUNCTION save_query() RETURNS trigger AS $$
    switch $TG_op {
    DELETE {
            spi_exec "INSERT INTO log_table (query) VALUES (current_query())"
        }
    default {
            return OK
        }
    }
    return OK
$$ LANGUAGE pltcl;

Creating a trigger:

create trigger test_trigger before delete on some_table for each row execute procedure save_query();

Prepared statement is executed from hibernate.

Edit again (java part added)

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;

public class DeleteUsingPreparedStmt {

    public static void main(String[] args) {
        try {
            String deleteString = "delete from floors where id = ? ";
            final int idToDelte = 1;

            Class.forName("org.postgresql.Driver");
            String url = "jdbc:postgresql://127.0.0.1:5432/YOUR_DATABASE";
            Connection conn = DriverManager.getConnection(url, "user", "password");

            PreparedStatement deleteStmt = conn.prepareStatement(deleteString);
            deleteStmt.setInt(1, idToDelte);
            deleteStmt.executeUpdate();
        } catch (Exception e) {
            //hide me :)
        }
    }
}

You need a jdbc driver - click.

Answer 1

Here is some working code (for Debian users: just install postgresql-pltcl-8.4 package and run CREATE LANGUAGE pltcl;)

CREATE TABLE log_table (
    id serial,
    query text
);

CREATE TABLE floors (
    id serial,
    value text
);

INSERT INTO floors(value) VALUES ('aaa'), ('bbb');

CREATE OR REPLACE FUNCTION save_query() RETURNS trigger AS $$
    switch $TG_op {
        DELETE {
            spi_exec "INSERT INTO log_table (query) VALUES (current_query())"
        }
        default {
            return OK
        }
    }
    return OK
$$ LANGUAGE pltcl;

CREATE TRIGGER test_trigger
    BEFORE DELETE ON floors
    FOR EACH ROW
    EXECUTE PROCEDURE save_query();

However I can't get placeholders in prepared statement (it returns EXECUTE deleteFromFloors(2);):

TABLE log_table;
 id | query 
----+-------
(0 rows)
DELETE FROM floors WHERE id = 1;
DELETE 1
TABLE log_table;
 id |              query               
----+----------------------------------
  1 | DELETE FROM floors WHERE id = 1;
(1 row)
PREPARE deleteFromFloors(integer) AS
    DELETE FROM floors WHERE id = $1;
PREPARE
EXECUTE deleteFromFloors(2);
DELETE 1
TABLE log_table;
 id |              query               
----+----------------------------------
  1 | DELETE FROM floors WHERE id = 1;
  2 | EXECUTE deleteFromFloors(2);
(2 rows)

EDIT:

As a workaround use OLD record (represented as array in Tcl), fetch id column from there and use replace function to put it instead of $1. Here you have two solutions: PL/pgSQL and PL/Tcl:

CREATE OR REPLACE FUNCTION save_query() RETURNS TRIGGER AS $$
BEGIN
    INSERT INTO log_table (query)
        VALUES (replace(current_query(), '$1', OLD.id::text));
    RETURN OLD;
END;
$$ LANGUAGE plpgsql;

CREATE OR REPLACE FUNCTION save_query() RETURNS trigger AS $$
    switch $TG_op {
        DELETE {
            spi_exec "INSERT INTO log_table (query)
                VALUES (replace(current_query(), '\$1', '$OLD(id)'))"
        }
        default {
            return OK
        }
    }
    return OK
$$ LANGUAGE pltcl;

Result:

java -classpath '.:postgresql-8.4-702.jdbc4.jar' DeleteUsingPreparedStmt

TABLE log_table;
 id |              query              
----+---------------------------------
  1 | delete from floors where id = 1

(1 row)