[web2py] How to flash a message after a callback

[Noel Villamor]

I have a button which does the following callback:

ajax('{{=URL('callback')}}',['btn1'],':eval');"

Then I have the following callback function in my controller:

def callback():
    db(db.tbl.id==100).update(data='sampledata')
    jquery = ???
    return jquery

I can use jquery = "alert('Lame table update message');" but it
doesn't appear as good as the response.flash message.

1) How do I emulate response.flash?
2) How to determine if the db update is successful or not so I can
flash the appropriate message.

Thanks!