org.apache.ojb.broker.accesslayer
Class MtoNCollectionPrefetcher

java.lang.Object
  org.apache.ojb.broker.accesslayer.BasePrefetcher
      org.apache.ojb.broker.accesslayer.RelationshipPrefetcherImpl
          org.apache.ojb.broker.accesslayer.CollectionPrefetcher
              org.apache.ojb.broker.accesslayer.MtoNCollectionPrefetcher

All Implemented Interfaces:

RelationshipPrefetcher

public class MtoNCollectionPrefetcher
extends CollectionPrefetcher

Relationship Prefetcher for MtoN-Collections.

Version:

$Id: MtoNCollectionPrefetcher.java,v 1.1 2007-08-24 22:17:30 ewestfal Exp $

Author:

Jakob Braeuchi

Field Summary

Fields inherited from class org.apache.ojb.broker.accesslayer.BasePrefetcher

IN_LIMIT, itemClassDesc, pkLimit

Constructor Summary

MtoNCollectionPrefetcher(PersistenceBrokerImpl aBroker, ObjectReferenceDescriptor anOrd)

Method Summary

protected void	associateBatched(Collection owners, Collection children, Collection mToNImplementors) associate the batched Children with their owner object loop over children BRJ: There is a potential problem with the type of the pks used to build the Identities.
protected Query[]	buildMtoNImplementorQueries(Collection owners, Collection children) Build the multiple queries for one relationship because of limitation of IN(...)
protected Query	buildMtoNImplementorQuery(Collection ids) Build a query to read the mn-implementors
protected Query	buildPrefetchQuery(Collection ids) Build the prefetch query for a M-N relationship, The query looks like the following sample :
void	prefetchRelationship(Collection owners) Prefetch the Relationship for the owners (the 1 side of a 1:n)

Methods inherited from class org.apache.ojb.broker.accesslayer.CollectionPrefetcher

associateBatched, buildPrefetchQueries, createCollection, getCollectionDescriptor

Methods inherited from class org.apache.ojb.broker.accesslayer.RelationshipPrefetcherImpl

getObjectReferenceDescriptor, getOwnerClassDescriptor, isCascadeRetrieve, prepareRelationshipSettings, restoreRelationshipSettings, setCascadeRetrieve, setObjectReferenceDescriptor

Methods inherited from class org.apache.ojb.broker.accesslayer.BasePrefetcher

buildPrefetchCriteria, buildPrefetchQuery, buildPrefetchQuery, getBroker, getDescriptorRepository, getItemClassDescriptor, getLimit, getLogger

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

MtoNCollectionPrefetcher

public MtoNCollectionPrefetcher(PersistenceBrokerImpl aBroker,
                                ObjectReferenceDescriptor anOrd)

Parameters:

aBroker - the PersistenceBroker

anOrd - the CollectionDescriptor

Method Detail

prefetchRelationship

public void prefetchRelationship(Collection owners)

Description copied from interface: RelationshipPrefetcher

Prefetch the Relationship for the owners (the 1 side of a 1:n)

Specified by:

prefetchRelationship in interface RelationshipPrefetcher

Overrides:

prefetchRelationship in class BasePrefetcher

See Also:

RelationshipPrefetcher.prefetchRelationship(Collection)

buildPrefetchQuery

protected Query buildPrefetchQuery(Collection ids)

Build the prefetch query for a M-N relationship, The query looks like the following sample :

       crit = new Criteria();
       crit.addIn("PERSON_PROJECT.PROJECT_ID", ids);
       crit.addEqualToField("id","PERSON_PROJECT.PERSON_ID");
       qry = new QueryByMtoNCriteria(Person.class, "PERSON_PROJECT", crit, true);
 

Overrides:

buildPrefetchQuery in class CollectionPrefetcher

Parameters:

ids - Collection containing all identities of objects of the M side

Returns:

the prefetch Query

buildMtoNImplementorQuery

protected Query buildMtoNImplementorQuery(Collection ids)

Build a query to read the mn-implementors

Parameters:

ids -

buildMtoNImplementorQueries

protected Query[] buildMtoNImplementorQueries(Collection owners,
                                              Collection children)

Build the multiple queries for one relationship because of limitation of IN(...)

Parameters:

owners - Collection containing all objects of the ONE side

associateBatched

protected void associateBatched(Collection owners,
                                Collection children,
                                Collection mToNImplementors)

associate the batched Children with their owner object loop over children

BRJ: There is a potential problem with the type of the pks used to build the Identities. When creating an Identity for the owner, the type of pk is defined by the instvars representing the pk. When creating the Identity based on the mToNImplementor the type of the pk is defined by the jdbc-type of field-descriptor of the referenced class. This type mismatch results in Identities not being equal. Integer[] {10,20,30} is not equal Long[] {10,20,30}

This problem is documented in defect OJB296. The conversion of the keys of the mToNImplementor should solve this problem.