Hi,
your mapping seems ok. Sounds like a bug in OJB.
I tried to reproduce your problem without success (using latest version
of OJB from SVN OJB_1_0_RELEASE branch) - never get a NPE.
I use the mapping from the m:n example (with Person and Project) and do:
oid = broker.serviceIdentity().buildIdentity(Person.class, new Integer(1));
person = (Person) broker.getObjectByIdentity(oid);
No NPE. How can I reproduce your problem?
regards,
Armin
Truong Nguyen Huy wrote:
Hi all,
I have a problem when using m:n mapping. I will describe it below.
I just implement a tutorial in this link
http://db.apache.org/ojb/docu/guides/basic-technique.html#Support+for+Non-Decomposed+m%3An+Mappings
There are three table: PERSON, PROJECT, PROJECT_PERSON.
PROJECT_PERSON is the connector standing for m:n relation between
PROJECT and PERSON.
PROJECT(id,name) PERSON(id,name) PROJECT_PERSON(project_id,
person_id)
The mapping file as below:____________________________
<!-- vn.com.tma.testOJB.Person -->
<class-descriptor class="vn.com.tma.testOJB.Person"
table="person" <field-descriptor name="id" column="id"
jdbc-type="INTEGER" primarykey="true" autoincrement="true" />
<field-descriptor name="name" column="name" jdbc-type="VARCHAR" />
<collection-descriptor name="projects" collection-class="
org.apache.ojb.broker.util.collections.ManageableArrayList"
element-class-ref="vn.com.tma.testOJB.Project" auto-retrieve="true"
auto-update="true" indirection-table="PROJECT_PERSON"
<fk-pointing-to-this-class column="PERSON_ID"/>
<fk-pointing-to-element-class column="PROJECT_ID"/>
</collection-descriptor>
</class-descriptor>
<!-- vn.com.tma.testOJB.Project -->
<class-descriptor class="vn.com.tma.testOJB.Project"
table="project" <field-descriptor name="id" column="id"
jdbc-type="INTEGER" primarykey="true" autoincrement="true" />
<field-descriptor name="name" column="Name" jdbc-type="VARCHAR" />
<collection-descriptor name="employees" collection-class="
org.apache.ojb.broker.util.collections.ManageableArrayList"
element-class-ref="vn.com.tma.testOJB.Person" auto-retrieve="true"
auto-update="false" indirection-table="PROJECT_PERSON"
<fk-pointing-to-this-class column="PROJECT_ID"/>
<fk-pointing-to-element-class column="PERSON_ID"/>
</collection-descriptor> </class-descriptor>
When I run these codes, it has error: PersistenceBroker broker =
PersistenceBrokerFactory.defaultPersistenceBroker(); Identity oid =
broker.serviceIdentity().buildIdentity(Person.class, new Integer(1));
Person person = (Person) broker.getObjectByIdentity(oid);
The error is caused by the third line. This is the exception stack:
Exception in thread "main"
org.apache.ojb.broker.PersistenceBrokerException:
java.lang.NullPointerException at
org.apache.ojb.broker.core.QueryReferenceBroker.getCollectionByQuery(Unknown
Source) at
org.apache.ojb.broker.core.QueryReferenceBroker.doRetrieveCollection(Unknown
Source) at
org.apache.ojb.broker.core.QueryReferenceBroker.retrieveCollection(Unknown
Source) at
org.apache.ojb.broker.core.QueryReferenceBroker.doRetrieveCollections(Unknown
Source) at
org.apache.ojb.broker.core.QueryReferenceBroker.retrieveCollections(Unknown
Source) at
org.apache.ojb.broker.core.PersistenceBrokerImpl.getDBObject(Unknown
Source) at
org.apache.ojb.broker.core.PersistenceBrokerImpl.doGetObjectByIdentity(Unknown
Source) at
org.apache.ojb.broker.core.PersistenceBrokerImpl.getObjectByIdentity(Unknown
Source) at
org.apache.ojb.broker.core.DelegatingPersistenceBroker.getObjectByIdentity(Unknown
Source) at
org.apache.ojb.broker.core.DelegatingPersistenceBroker.getObjectByIdentity(Unknown
Source) at vn.com.tma.main.Run.main(Run.java:41) Caused by:
java.lang.NullPointerException at
org.apache.ojb.broker.accesslayer.MtoNCollectionPrefetcher.associateBatched(Unknown
Source) at
org.apache.ojb.broker.accesslayer.MtoNCollectionPrefetcher.prefetchRelationship(Unknown
Source) at
org.apache.ojb.broker.core.QueryReferenceBroker.performRetrievalTasks(Unknown
Source) at
org.apache.ojb.broker.core.QueryReferenceBroker.getCollectionByQuery(Unknown
Source) ... 11 more
But if I change auto-archive to "false" in arbitrary one of two
class-descriptor, there is no error anymore. But it still causes the
same error when I use method "broker.retrieveAllReferences()" on an
instance of the rest class-descriptor.
Only when I change auto-archive of both class-descriptor to "false",
the error is omitted.
Can anyone explain why and help me resolve the problem when using
auto-archive="true" on both class-descriptor? Thank you very for your
help.
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