Thread: How can I refer to an ANYELEMENT variable in postgresql dynamic SQL?

Cross-posting from stackoverflow in the hope of getting some additional eyes on the question.

http://stackoverflow.com/questions/28505782/how-can-i-refer-to-an-anyelement-variable-in-postgresql-dynamic-sql

I'm trying to write a PostgreSQL function for table upserts that can be used for any table. My starting point is taken from a concrete function for a specific table type:

CREATE TABLE doodad(id BIGINT PRIMARY KEY, data JSON);
CREATE OR REPLACE FUNCTION upsert_doodad(d doodad) RETURNS VOID AS
  $BODY$
BEGIN
  LOOP
    UPDATE doodad
       SET id = (d).id, data = (d).data
     WHERE id = (d).id;
    IF found THEN
      RETURN;
    END IF;

    -- does not exist, or was just deleted.

    BEGIN
      INSERT INTO doodad SELECT d.*;
      RETURN;
    EXCEPTION when UNIQUE_VIOLATION THEN
      -- do nothing, and loop to try the update again
    END;

  END LOOP;
END;
  $BODY$
LANGUAGE plpgsql;

The dynamic SQL version of this for any table that I've come up with is here: SQL Fiddle

CREATE OR REPLACE FUNCTION upsert(target ANYELEMENT) RETURNS VOID AS
$
DECLARE
  attr_name NAME;
  col TEXT;
  selectors TEXT[];
  setters TEXT[];
  update_stmt TEXT;
  insert_stmt TEXT;
BEGIN
  FOR attr_name IN SELECT a.attname
                     FROM pg_index i
                     JOIN pg_attribute a ON a.attrelid = i.indrelid
                                        AND a.attnum = ANY(i.indkey)
                    WHERE i.indrelid = format_type(pg_typeof(target), NULL)::regclass
                      AND i.indisprimary
  LOOP
    selectors := array_append(selectors, format('%1$s = target.%1$s', attr_name));
  END LOOP;

  FOR col IN SELECT json_object_keys(row_to_json(target))
  LOOP
    setters := array_append(setters, format('%1$s = (target).%1$s', col));
  END LOOP;

  update_stmt := format(
    'UPDATE %s SET %s WHERE %s',
    pg_typeof(target),
    array_to_string(setters, ', '),
    array_to_string(selectors, ' AND ')
  );
  insert_stmt := format('INSERT INTO %s SELECT (target).*', pg_typeof(target));

  LOOP
    EXECUTE update_stmt;
    IF found THEN
      RETURN;
    END IF;

    BEGIN
      EXECUTE insert_stmt;
      RETURN;
    EXCEPTION when UNIQUE_VIOLATION THEN
      -- do nothing
    END;
  END LOOP;
END;
$
LANGUAGE plpgsql;

When I attempt to use this function, I get an error:

SELECT * FROM upsert(ROW(1,'{}')::doodad);

ERROR: column "target" does not exist: SELECT * FROM upsert(ROW(1,'{}')::doodad)

I tried changing the upsert statement to use placeholders, but I can't figure out how to invoke it using the record:

EXECUTE update_stmt USING target;

ERROR: there is no parameter $2: SELECT * FROM upsert(ROW(1,'{}')::doodad)

EXECUTE update_stmt USING target.*;

ERROR: query "SELECT target.*" returned 2 columns: SELECT * FROM upsert(ROW(1,'{}')::doodad)

I feel really close to a solution, but I can't figure out the syntax issues.



--

Christopher Currie

Engineering, Usermind

codemonkey@usermind.com

206.353.2867 x109