Re: Problems saving a m:n relationship

[Armin Waibel]

Hi Stijn,

a few days ago I wrote some tests for M:N handling in odmg-api and 
stumble across the same problem (hope we can fix this soon). There are 
two possible workarounds:

Transaction tx = odmg.newTransaction();
tx.begin();
Iterator it = person.getAddresses().iterator();
while(it.hasNext())
{
   database.makePersistent(it.next());
}
database.makePersistent(person);
tx.commit();
or you can use the pb-api to insert your object (this looks a little bit 
complex, because you have to set auto-update/delete false when using 
odmg-api):

TransactionExt tx = (TransactionExt) odmg.newTransaction();
tx.begin();
PersistenceBroker pb = tx.getBroker();
Iterator it = person.getAddresses().iterator();
while(it.hasNext())
{
   pb.store(it.next());
}
pb.store(person);
pb.serviceBrokerHelper().link(person, true);
tx.commit();
Hope this will help you.

regards,
Armin
Stijn de Witt wrote:

Hi,

I have a problem trying to persist two objects that are related through an indirection table. This is what my tables look like:

-----
PERSON
id
firstname
lastname
...
ADDRESS
id
street
housenr
...
PERSON_ADDRESS
person_id
address_id
-----
I have chosen for this construction, because COMPANY can have multiple addresses 
too, so I don't want a column person_id in ADDRESS. One address doesn't have to be 
available for multiple PERSON's or COMPANY's or whatever, so it actually is more of a 
1:n relationship using an indirection table. So PERSON_ADDRESS will often contain the 
same person_id multiple times, but not the same address_id.
I've read the tutorials, but I don't get it to work. I'll show (a fragment of) our 
repository_user.xml:
-----
<class-descriptor
    class="nl.bergland.codamo.Address"
    table="bit_Address"
    <field-descriptor
        name="id"
        column="id"
        jdbc-type="INTEGER"
        primarykey="true"
        length="11"
    >
    </field-descriptor>
    <field-descriptor
        name="street"
        column="street"
        jdbc-type="VARCHAR"
        length="64"
    >
    </field-descriptor>
    <field-descriptor
        name="houseNr"
        column="houseNr"
        jdbc-type="VARCHAR"
        length="16"
    >
    </field-descriptor>
</class-descriptor>
<class-descriptor
    class="nl.bergland.codamo.Person"
    table="bit_Person"
    <field-descriptor
        name="id"
        column="id"
        jdbc-type="INTEGER"
        primarykey="true"
        length="11"
    >
    </field-descriptor>
    <field-descriptor
        name="firstName"
        column="firstName"
        jdbc-type="VARCHAR"
        length="24"
    >
    </field-descriptor>
    <field-descriptor
        name="lastName"
        column="lastName"
        jdbc-type="VARCHAR"
        length="24"
    >
    </field-descriptor>
    <collection-descriptor
        name="addresses"
        element-class-ref="nl.bergland.codamo.Address"
        indirection-table="bit_PersonAddress"
        auto-retrieve="true"
        auto-update="true"
        auto-delete="true"
    >
        <fk-pointing-to-this-class column="personId"/>
        <fk-pointing-to-element-class column="addressId"/>
    </collection-descriptor>
</class-descriptor>
-----
The generated tables in mysql seem to be ok with me (we actually use OjbDoclet to generate the repository.xml and the SQL) and insertion of a PERSON works fine. However, when we create a new person, add a new Address to it and try to save the person, the following happens:

A new record gets created for PERSON fine
A new record gets created for ADDRESS fine, but when I set auto-update to true, 2 get 
created??
A new record gets created for PERSON_ADDRESS, but both the columns person_id and 
address_id are set to 0.
Our save code looks something like this:

-----
        Person person = new Person;
        person.getAddresses().add(new Address());
        Implementation impl = OJB.getInstance();
        Database db = impl.newDatabase();
        
        db.open("default", Database.OPEN_READ_WRITE);        
        Transaction tx = impl.newTransaction();        
        tx.begin();
        
        // establish database locks on all root dataobjects
        tx.lock(person, Transaction.WRITE);
        

        // set person and address values
        // ...
        
        tx.commit();
        db.close();
-----

A lot of info for a first-time post, I hope this problem sounds familiar to 
someone here.
Thanks,
-Stijn


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