Hello

Function field signature:

 (self, cr, uid, ids, field_name, arg, context=None):

and you need to return the result for each id in ids...

So if it's the same for each ids:

dict.fromkeys(ids, result)

==>  You shloud have something like that...

def _total_get(self, cr, uid, ids, fieldname, arg, context=None):
    cr.execute('select total from hr_payslip_line where code = "22001"')
    # supposing you are waiting only one element ??? always for this code 22001 ? 
    total = cr.fetchone()[0];
    return dict.fromkeys(ids, total)

But it's a strange case... Usually, we want a result distinct according the id given...

Let us know if it's work for you !