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
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