On Dec 12, 2006, at 1:45 PM, Craig L Russell wrote:

> There's nothing that I can find in the JPA specification about  
> preserving null vs. empty Collections and Maps. There's no good  
> (practical) way to implement null values for these types in  
> relational databases, which is the target of the specification.
>
> 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.

CMP2 requires that collection valued fields always be non-null (i.e.,  
you always get an empty collection).  I wanted to know what  
guarantees JPA provided in terms of the field being not null.   
Specifically, if the field is set to null when an empty collection is  
loaded, I would have to compensate for that in my framework code.   
Since, JPA does the intelligent thing and inserts an empty  
collection, my job is easier.

-dain