No select permission on a table but can query it

I think that this is a strange question, but: I need to revoke the
select permission on a table, but I also need to leave, with a function,
a user do a query on column.
A real case can be that a user "test" cannot have the permissions for do
a "select * from articles", but for do a "select has_article('an_article')"
where has_article are:

FUNCTION has_article (text) RETURNS articles AS $$
SELECT * from articles WHERE id_article=$1;
$$ LANGUAGE SQL

Into my tries I receive always a
ERROR: permission denied for relation articles

It's there a solution?

Thanks,
Michele