text search query building in postgres

I need to build a stored procedure that takes input an array of varchars . It will search for these using syntax like

SELECT *
FROM mytable
WHERE search_index @@ to_tsquery(' ');

If i give input to the procedure like tom ,dick,harry the query should be dynamically build like

SELECT *
FROM mytable
WHERE search_index @@ to_tsquery('tom | dick | harry ');


CREATE OR REPLACE FUNCTION text_search(search_terms character varying[], ent_id bigint)
  RETURNS entity_base AS

$BODY$DECLARE

  result_data entity_base;

  search_data text;
BEGIN

     search_data := array_to_string('sea开发者_Go百科rch_terms[]', '|');

     SELECT * INTO result_data FROM entity_base WHERE search_index @@ to_tsquery(search_data) and entity_id = ent_id;
     RETURN result_data;
END;$BODY$
  LANGUAGE 'plpgsql' VOLATILE
  COST 100;

When i run this im getting error

ERROR:  could not determine polymorphic type because input has type "unknown"
CONTEXT:  SQL statement "SELECT  array_to_string('search_terms[]', '|')"
PL/pgSQL function "text_search" line 5 at assignment

********** Error **********

ERROR: could not determine polymorphic type because input has type "unknown"
SQL state: 42804
Context: SQL statement "SELECT  array_to_string('search_terms[]', '|')"
PL/pgSQL function "text_search" line 5 at assignment

Use array_to_string().