Inserting NEW.* from a generic trigger using EXECUTE in PL/pgsql

Question

I have a number of tables that use the Postgres "Partitioning" feature. I want to define a common BEFORE INSERT OF ROW trigger on each table that will 1) dynamically create the partition should the insert occur against the parent table and 2) re-execute the insert against the partition.

Something like:

CREATE OR REPLACE FUNCTION partition_insert_redirect( )
RETURNS trigger AS $BODY$
BEGIN
  ... create the new partition and set up the redirect Rules ...

  /* Redo the INSERT dynamically.  The new RULE will redirect it to the child table */
  EXECUTE 'INSERT INTO ' || quote_ident(TG_TABLE_SCHEMA) || '.' || quote_ident(TG_TABLE_NAME) ||
          ' SELECT NEW.*'
END

But the "NEW" record isn't visible inside the EXECUTE SQL. How can I make this work as simply as possible?

As an alternative, can I iterate over the fields in the NEW record somehow?

I've thought of using a temp-table:

EXECUTE 'CREATE TEMPORARY TABLE new_row (LIKE ' ||
        quote_ident(TG_TABLE_SCHEMA) || '.' || quote_ident(TG_TABLE_NAME) ||
        ') ON COMMIT DROP';

INSERT INTO new_row SELECT NEW.*;

EXECUTE 'INSERT INTO ' || quote_ident(TG_TABLE_SCHEMA) || '.' || quote_ident(TG_TABLE_NAME) ||
       ' SELECT * FROM new_row';
DROP TABLE new_row;

But this also doesn't work because of the cached reference to a temp-table: Why do I get "relation with OID ##### does not exist" errors when accessing temporary tables in PL/PgSQL functions?

I'm using Postgres 8.2 and I can't change to any other version.

EDIT:
As @alvherre pointed out, this can probably be done in Postgres 8.4 with the EXECUTE ... USING syntax. See an example at http://wiki.postgresql.org/wiki/PL/pgSQL_Dynamic_Triggers

Answer 1

You can use EXECUTE USING to pass NEW to it. Your example would be

EXECUTE 'INSERT INTO ' || TG_RELID || '::regclass SELECT $1' USING NEW;

(Note that I use TG_RELID casted to regclass instead of fiddling with TG_TABLE_SCHEMA and TABLE_NAME because it is easier to use, if nonstandard. But then, plpgsql is nonstandard anyway.)

Answer 2

I've managed to get this to work by dynamically compiling a function that accepts the NEW row as a parameter:

    EXECUTE 'create or replace function partition_insert(r ' || TG_TABLE_NAME || ') RETURNS void AS $FUNC$' || 
            'BEGIN ' ||
                'insert into ' || TG_TABLE_NAME || ' SELECT r.*; ' ||
            'END $FUNC$ LANGUAGE plpgsql VOLATILE';
    PERFORM partition_insert(NEW);

As Postgres functions are polymorphic, this will generate a different function for each table that uses this trigger.

Despite being an ugly kludge, this seems to do the job.

Although it looks like I could define each polymorphic variation up front when I build the system, because of caching, I must recompile the function whenever I create or drop a child table so that the function uses the latest insert RULE.

EDIT: Additional wrinkles
There's a little gotcha with this technique: If this EXECUTE/PERFORM action is rolled-back on the first attempt due to another error (for example, in my case a CHECK constraint failure) then the function containing this code seems to cache a reference to the rolled-back partition_insert() function it created using the EXECUTE and subsequent calls fail due to a cached object not being found.

I resolved this by pre-creating stub versions of the function for each required table-type parameter when I define the database.

Answer 3

Yes, you can use EXPLAIN ... USING in 8.4. For example:

EXECUTE 'INSERT INTO ' || table_name || ' SELECT $1.*' USING NEW;

In lower versions (I've only tested in 8.3), you can use:

EXECUTE 'INSERT INTO ' || table_name ||
    ' SELECT (' || quote_literal(NEW) || '::' || TG_RELID::regclass || ').*';