Conversion or transformation ?

Question

Hi,
In our domain model, we have many enumerated types, or in other words, classes with a finite number of read-only instances . A good example would be a class named Country. This class has some attributes and a unique identifier.
Since all this stuff is read-only, does such a class need to have its own database table ? A class having a one-to-one relation with a Country could store the country identifier and Toplink use it to resolve to the single in-memory instance, avoiding an access to Country table.
I'm not sure if this is good design. And if it is, I don't know how to configure Toplink to do this. Conversion, transformation, variable one-to-one mapping ???
Any comments would be appreciated
Jean-Christian Gagné

Answer 1

Jean-Christian,
A little confused by your question. Do you want to have the table at all or are you just trying to avoid the read on the table each time.
If you are trying to avoid the read then I would suggest keeping the 1:1 mapping and pre-loading all Country instances at system startup. This is common for reference data and will avoid any additional queries on the table.
If you wish to eliminate the Country table then you have a couple of options to handle the country-code to Country instance conversion.
1. Use an ObjectTypeMapping and populate it at startup time with the static set of Country instances
2. Use a TypeConversionMapping and specify the database type as String/int (whatever the code is). The object type will automatically be found in the mapped class. Then extend the ConversionManager to also support you Country class conversion to and from the code type. (see http://otn.oracle.com/products/ias/toplink/technical/tips/customconversion/index.html).
Doug