Example of a custom field mapping?

Question

Ok, I admit it I am struggling here. I have simplified my example from
what I actually have.
I have a table that models a flat hierarchy
ID | START_DATE | END_DATE | CLASSNAME | FIELD1 | FIELD2 | ...
one of the objects in my hiearchy (CashFlow) has a field that is in fact
another object called DatePeriod that contains two fields startDate and
endDate.
I understand that what I am trying to do is embed the DatePeriod object
inside of the larger object when it get's persisted.
I have the following metadata set-up
<class name="CashFlow" persistence-capable-superclass="InstrumentFlow">
<extension vendor-name="kodo" key="table" value="INSTRUMENT_FLOW"/>
<extension vendor-name="kodo" key="pk-column" value="ID"/>
<extension vendor-name="kodo" key="class-column" value="none"/>
<extension vendor-name="kodo" key="lock-column" value="none"/>
<field name="accrualPeriod" embedded="true"/>
</class>
and for my DatePeriod object
<class name="DatePeriod">
<extension vendor-name="kodo" key="table" value="INSTRUMENT_FLOW"/>
<extension vendor-name="kodo" key="pk-column" value="ID"/>
<extension vendor-name="kodo" key="lock-column" value="none"/>
<extension vendor-name="kodo" key="class-column" value="none"/>
<field name="startDate">
<extension vendor-name="kodo" key="data-column" value="START_DATE"/>
</field>
<field name="endDate">
<extension vendor-name="kodo" key="data-column" value="END_DATE"/>
</field>
</class>
Every time I try to fetch a CashFlow object I get an error as KODO is
trying to select the column 'ACCRUALPERIODX.'
What am I doing wrong? Do I need to use a custom field mapping? If so
where is the documentation to help me write a custom field mapping?
A second question would be what happens if the DatePeriod object is used
in a couple of places, I don't want to tie it's persistence to the
INSTRUMENT_FLOW table.
All help gratefully received
Cheers
Matt

Answer 1

As you suspect, Kodo 2.x does not support embedded class mappings. Kodo
3.0 will support embedded mappings.
In the meantime, you can create a custom mapping, but unfortunately our
documentation for custom mappings is lacking right now. Given how simple
your DatePeriod object is, you're probably better off with something
simpler (and as a bonus, less bound to Kodo):
Just make your DatePeriod class and the field that holds the DatePeriod
instance non-persistent. In the class that has the (now non-persistent)
DatePeriod field, add two new persistent fields for the startDate and
endDate. Then just use internal logic to construct the DatePeriod from
the startDate and endDate. You can do this using the
javax.jdo.InstanceCallbacks methods, or just do the logic in your setter
and getter methods for the DatePeriod.