Hi again,
> > I'm right now trying to create the mapping for 2 class I've developped:
> > - A contains a Collection of class B
> > - B doesn't have any relation back to A
> >
> > With my current understanding of OJB, I'll need to create in B a
> > reference
> > back to A to be able to make the mapping (using an inverse-foreignkey
> > element). Is that right ? If yes why ?
>
> What you need is not a full reference object pointing back to A, but an
> attribute that holds the foreign attribute.
>
> If the table A has a Primary key A_ID then the B table must contain a
> column FK_A_ID to allow the RDBMS to manage the foreign constraints.
>
> OJB simply parallels the foreign mechanisms of relational databases here
> and thus you need attributes in your persistent classes to hold
> primary- and foreign-key data.
I still have some problem to understand this.
So I have 2 tables:
- TABLE_A containing a field A_ID
- TABLE_B containing a field B_ID and a field FK_A_ID
I also have 2 classes for persistence:
- A containing an attribute collectionOfBs and another atribute id
- B containing an attribute id
In this case, I think I _need_ to add an extra attribute to the B classes
idOfA, so I can make the mapping:
<class-descriptor class="A"
table="TABLE_A">
<field-descriptor id="1"
name="id"
column="A_ID"
jdbc-type="INTEGER"
primarykey="true"
autoincrement="true"/>
<collection-descriptor
name="collectionOfBs"
element-class-ref="B">
<inverse-foreignkey field-id-ref="2"/>
</collection-descriptor>
</class-descriptor>
<class-descriptor class="B"
table="TABLE_B">
<field-descriptor id="1"
name="id"
column="B_ID"
jdbc-type="INTEGER"
primarykey="true"
autoincrement="true"/>
<field-descriptor id="2"
name="idOfA"
column="FK_A_ID"
jdbc-type="INTEGER"
primarykey="true"
autoincrement="true"/>
</class-descriptor>
In my case, there is really no need for the idOfA attribute in B. B objects
are aggregated to A object.
I do not think that there is a need for this back reference.
Cheerio,
Guillaume
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