tsearch2() with data from other table

Hi,

I have a table with items.
One field is site_user, which fk:s the user row that owns the item.

There are a few fields i throw to tsearch2() via an index right now,
but one user wanted his name to be in the search as well. So, what I
would want to do is:

CREATE FUNCTION euits(int)
RETURNS text AS 'select username || \' \' || firstname || \' \' ||
lastname from site_user where objectid = $1;' LANGUAGE SQL;

CREATE TRIGGER site_item_fts
BEFORE UPDATE OR INSERT ON site_item
FOR EACH ROW EXECUTE PROCEDURE
tsearch2(idxfti, name, keywords, keywords_cb, location_country,
location_city, media_source, description, euits, site_user);

Pg accepts this, but when I

update site_item
set
     description = description

I get:
Query executed in 78 ms, 6 Row(s) Affected
WARNING:  TSearch: 'site_user' is not of character type
WARNING:  TSearch: 'site_user' is not of character type
...

I suppose I am doing something stupid here? If I remove euits
I still receive the same error.

Any suggestions are very welcome.

Best regards,
Marcus