[Objectbridge-developers] optional relationships

[Dirk O. <di...@xa...>]

Hi,

I just started using ObjectBridge for a small hobby project. I use it
with the FrontBase dbms which had me digging around in the source a bit
to make it work (wasn't hard). Now I found a problem which I could
easily work around but since tihs is a common modeling case I thought of
a general solution.

To illustrate things better I'll just give a short description of my
tables: I have a table 'Person' which has a to-many relationship to the
table 'Folder'. The 'Folder' table will later have a reflexive
relationship to itself (so I can have subfolders to every folder). (BTW:
is that possible with ObjectBridge right now?)

In order to model that, the 'Folder' table needs a foreign key which can
be NULL for the case that a folder has no parent folder. 

This empty foreign key already throws an exception when trying to
resolve the relationship from User to Folder. Since JdbcAccess tries to
put values into the Folder instance using reflection it stumbles when
trying to set the null foreign key.

While I could work around this giving the Folder a special foreign key
(e.g. 0) for the no-parent-folder case I think such cases should be
handled by the framework. Currently, I could think of two possible
solutions to the problem:

1) extend the mapping to let the user specify which value object he
wants to have assigned for individual attributes. So there would be a
<field.valueType/> in addition <field.name/> node in the mapping XML
file. This would allow for e.g. Integer values to be passed. To make
this work with reflection, JdbcAccess should use a set method if that's
available (could be found out using reflection)

2) define an interface with methods that could let the instance itself
decide what to do in such cases. E.g. we could have a method named
"unableToTakeNullForField(String fieldName)".

Does anyone have a better idea?

-dirk