Id column values for null objects

Question

If I have something like the following, where B.id is mapped to an INTEGER
column in A's table, Kodo wants to store a NULL value into the column. This
doesn't work if the column is specified as NOT NULL. Is there a way to
configure Kodo to use some predefined integer value instead, such as 0
or -1?
class A {
int id;
B b;
class B {
int id;
A a = new A();
a.id = 123;
a.b = null;
pm.makePersistent(a);
pm.currentTransaction().commit();

Answer 1

I'm not sure what you mean by "value mapping." In my case, I am mapping a
null reference to another object. I am using application identity. Here's a
more complete example (still very abbreviated, but hopefully complete
enough):
class A {
static class Id { int id; }
int id;
B b;
class B {
static class Id { int id; }
int id;
int value;
create table A (ID integer not null, BID integer not null)
create table B (ID integer not null, VALUE integer)
<jdo>
<package name="test">
<class name="A" objectid-class="A$Id">
<extension vendor-name="kodo" key="table" value="A"/>
<field name="id" primary-key="true">
<extension vendor-name="kodo" key="data-column" value="ID"/>
</field>
<field name="b">
<extension vendor-name="kodo" key="id-data-column" value="BID"/>
</field>
</class>
<class name="B" objectid-class="B$Id">
<extension vendor-name="kodo" key="table" value="B"/>
<field name="id" primary-key="true">
<extension vendor-name="kodo" key="data-column" value="ID"/>
</field>
<field name="value">
<extension vendor-name="kodo" key="data-column" value="VALUE"/>
</field>
</class>
</package>
</jdo>
A a1 = new A();
a1.id = 123;
a1.b = new B();
a1.b.id = 456;
a1.b.value = 999;
pm.makePersistent(a1);
A a2 = new A();
a2.id = 789;
a1.b = null;
pm.makePersistent(a2);
pm.currentTransaction().commit();
The inserts for table A look something like this:
insert into A (ID, BID) values (123, 456)
insert into B (ID, VALUE) values (456, 999)
insert into A (ID, BID) values (789, NULL)
The NULL value fails because the column is specified as NOT NULL
(pre-existing schema scenario).
What I need to be able to do is specify what value gets inserted for null
object references. Kodo is inserting NULL. I need to insert -1.