Re: Manual Link and Unlink question

[Armin Waibel]

Hi Brad,
Bradford Pielech wrote:
Hello:
    This is a follow on to my question from last week where I have a 
graph structure where each graph node has a list of parents and 
children.  I was trying to use the auto-update=object and 
auto-delete=object features, but it was not working well in my 
particular scenario (meaning there were not any bugs in OJB) so I am 
investigating switching to auto-update and auto-delete = none and 
linking / unlinking on my own.

    So here is my question: if I have object A and object B already 
stored in the database, how can I create or delete an M to N link 
between them in their indirection table? I know that the BrokerHelper 
link and unlink methods are the way to go, but I cannot see how to use 
it because, to me, it looks like you can only specify 1 side of the link.
If you specify one side of the link this should be enough, because in 
indirection table the FK of both objects are inserted - or I'm missing 
something?
For example:
A, B already existing.
// declare relation
A.addBs(B)
broker.beginTx
broker.serviceBrokerHelper().link(A);
broker.commitTx

After this in indirection table the m:n relation between A and B should 
be stored.

If you now call
broker.retrieveAllReferences(B)
Collection result = B.getAs()
B now should contain A
There is a test case in test suite ([db-ojb/src/test]) called 
org.apache.ojb.broker.M2NTest handle with m:n relation (automatic store 
and custom store with linking)

regards,
Armin
    Here is some rough sample code of what I want to do:
-----------
    PersistenceBroker pbroker = 
PersistenceBrokerFactory.defaultPersistenceBroker();
    pbroker.beginTransaction();
    pbroker.store(a);
    pbroker.commitTransaction();

    //then some time later
    pbroker.beginTransaction();
    pbroker.store(a);
    pbroker.commitTransaction();
    //and finally even later
    pbroker.serviceBrokerHelper().link(a,b); //I know this method 
doesn't exist, but this is what I want to do.
    //  or
    pbroker.serviceBrokerHelper().unlink(a,b);
-------------

Here is what the repository file for the DAGNode looks like:
<collection-descriptor
        name="children"
        element-class-ref="DAGNode"
        indirection-table="parent_children_table"
        auto-retrieve="true"
        auto-update="none"
        auto-delete="none"
    >
        <fk-pointing-to-this-class column="parent_id"/>
        <fk-pointing-to-element-class column="child_id"/>
    </collection-descriptor>
    <collection-descriptor
        name="parents"
        element-class-ref="DAGNode"
        indirection-table="parent_children_table"
        auto-retrieve="true"
        auto-update="none"
        auto-delete="none"
    >
        <fk-pointing-to-this-class column="child_id"/>
        <fk-pointing-to-element-class column="parent_id"/>
thank you!
Brad


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