Design Issue: unique value

[Joe Baldwin]

This is an upper level design question associated with how to best  
generate a unique value using Cayenne and MySQL.

Step 1:
I have an existent Entity with a primary key (oid).  Per the Cayenne- 
recommended best practices I am avoiding direct access of this primary  
key and have created another attribute (orderID) that must be unique.   
So upon doing my Cayenne homework I read that the standard behavior in  
the DBMS model and the ORM model is to support only one auto-generated  
column and this is typically the PK column not related to my data  
abstraction.

Step 2:
So then I thought, well I will just use the MySQL "MAX()" function,  
find the max value, increment and voila I have generate my own unique  
number. When I tried to implement this design I ran into problems with  
SQLTemplate query attempting to bind the result of MAX(orderID) to an  
existent data object.

Step 3:
I guess I could always execute a "select *" on the entity and find the  
max attribute-value with a "for" loop, but that seems kind of  
Neanderthal.  OK, so I am now thinking someone must have solved this  
sort of design issue before I bumped into it.  What is the best way to  
solve this issue using Cayenne design patterns?

Thanks,
Joe