Updating 3-table dataset

Hi all,
    I don't know if that's the heat burning my brain but I can't find a
solution to what seemed a simple operation to me.

I have 3 tables
create table t_all
{
id uuid,
ref_id uuid     (FK to t_ana.id)
};
create table t_ana
{
id uuid,
code text
};
create table t_app
{
id uuid,
code text    (subset of t_ana.code)
}
I need to update t_all set t_all.id = t_app.id having t_ana.code in
t_app.code (I wrote it in some kind of meta-sql but I hope it's clear)
I tried to create a view but I need an INSTEAD OF trigger, since it
spreads among 3 tables so I hope there's some faster path to achieve the
solution....

Thanks
Moreno