The only way I know to do it is to redundantly add a column to the table whose mapped class contains the Collection or Map field that knows whether an empty Collection or Map should be presented to the user as null. This was deemed by the JPA experts to be non-trivial and non-demanded by users.
I am curious why this issue came up while trying to implement CMP 2 via JPA.
Craig On Dec 11, 2006, at 3:00 PM, Abe White wrote:
1. Loaded instances last stored with a null or empty collection/map are restored with an empty collection/map, period. You can ignore all the talk about null indicators. 2. Instances you construct yourself will maintain their null vs. empty field values at least until persist. Beyond that you shouldn't rely on null collections and maps remaining null -- they might become empty. 3. Pinaki's tip shows how to tell OpenJPA to throw an exception if you attempt to add an entity of the wrong type to a persistent collection/map field.________________________________________________________________ _______ Notice: This email message, together with any attachments, may contain information of BEA Systems, Inc., its subsidiaries and affiliated entities, that may be confidential, proprietary, copyrighted and/or legally privileged, and is intended solely for the use of the individual or entity named in this message. If you are not the intended recipient, and have received this message in error, please immediately return thisby email and then delete it.
Craig Russell Architect, Sun Java Enterprise System http://java.sun.com/products/jdo 408 276-5638 mailto:[EMAIL PROTECTED] P.S. A good JDO? O, Gasp!
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