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From conflue...@apache.org
Subject [CONF] Apache Jackrabbit: Mapping Bean Fields (page edited)
Date Wed, 20 Feb 2008 20:41:00 GMT
Mapping Bean Fields (JCR) edited by Jukka Zitting
      Page: http://cwiki.apache.org/confluence/display/JCR/Mapping+Bean+Fields
   Changes: http://cwiki.apache.org/confluence/pages/diffpagesbyversion.action?pageId=75361&originalVersion=1&revisedVersion=2

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 The bean-descriptor maps a bean attribute into one JCR node           (or a set of properties).
Generally, this attribute is an           object based on a custom class.

 Based on our model defined here,           the following bean-descriptor is used to map the
bean field           "pageInfo" (PageInfo class) into the JCR node called "pageInfo".

 The PageInfo class has a corresponding class-descriptor in the           mapping file. By
this way, the Persistence Manager can map each           PageInfo attributes. It is not necessary
to specify the type in           the bean-descriptor. The Persistence Manager uses the Java
          introspection to get information on the each bean fields.

h2. The JCR Structure

Following our example, the resulting JCR structure is:

{code}
/mysite/page1
  /mysite/page1/pageInfo
       my:title = "This is my page title"
       my:description = "This is my page description"
  ... other subnodes for page1 ...
{code}

By default, the persistence manager will create a subnode           (/mysite/page1/pageInfo)
for the bean-descriptor pageInfo.

h2. Using Another Bean Converter

The OCM framework gives you the freedom to choose another kind            of mapping for bean
fields. For example, you can use a custom            bean converter to access to the parent
node (see the next            section below).

This can be done by writing your own bean converter class and            reference this class
in the bean-descriptor.

h3. Predefined Bean Converters

 Here is the list of existing custom  bean converters:
|| Custom Bean Converter Class || Description ||
| org.apache.jackrabbit.ocm.persistence.beanconverter.impl.ParentBeanConverterImpl | Map a
bean field to the parent node. it is used to access to the               parent object in
read-only mode. See below the example based on               a Folder object. |
| org.apache.jackrabbit.ocm.persistence.beanconverter.impl.InlineBeanConverterImpl | Bean
converter used to map some node properties into one nested               bean field. The corresponding
bean field is not associated to a               subnode. |

If you want to use one of this bean converter, you have to           reference it into a bean-field
descriptor.

The following descriptor bean-descriptor contains a reference to           its parent folder
(parentFolder attribute). Now the CmsObjectImpl           object has an attribute (parentFolder)
that contains a reference           to the parent node.

{code}
<class-descriptor
    className="org.apache.jackrabbit.ocm.testmodel.inheritance.impl.CmsObjectImpl"
    jcrType="my:cmsobjectimpl" >
  <field-descriptor fieldName="path" path="true" />
  <field-descriptor fieldName="name" jcrName="my:name" id="true" />
  <bean-descriptor
      fieldName="parentFolder"
      converter="org.apache.jackrabbit.ocm.persistence.beanconverter.impl.ParentBeanConverterImpl"
/>
</class-descriptor>
{code}

h3. Building your own Bean Converters

Here is the different steps used to create a new bean converter :

First, specify the converter class in the bean descriptor:

{code}
<class-descriptor
    className="org.apache.jackrabbit.ocm.testmodel.inheritance.impl.CmsObjectImpl"
    jcrType="my:cmsobjectimpl" >
  <bean-descriptor
      fieldName="parentFolder"
      converter="org.apache.jackrabbit.ocm.persistence.beanconverter.impl.ParentBeanConverterImpl"
/>
</class-descriptor>
{code}

Then, implement the converter class (based on the interface           org.apache.jackrabbit.ocm.persistence.beanconverter.BeanConverter).

Your bean converter class can also extends the class           AbstractBeanConverterImpl to
have a default implementation for           some methods.

{code:title=ParentBeanConverterImpl.java}
import javax.jcr.Node;
import javax.jcr.Session;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.jackrabbit.ocm.exception.JcrMappingException;
import org.apache.jackrabbit.ocm.exception.PersistenceException;
import org.apache.jackrabbit.ocm.exception.RepositoryException;
import org.apache.jackrabbit.ocm.mapper.Mapper;
import org.apache.jackrabbit.ocm.mapper.model.BeanDescriptor;
import org.apache.jackrabbit.ocm.mapper.model.ClassDescriptor;
import org.apache.jackrabbit.ocm.persistence.atomictypeconverter.AtomicTypeConverterProvider;
import org.apache.jackrabbit.ocm.persistence.beanconverter.BeanConverter;
import org.apache.jackrabbit.ocm.persistence.objectconverter.ObjectConverter;
/**
 *
 * Bean converter used to access to the parent object.
 *
 *
 * @author <a href="mailto:christophe.lombart@gmail.com">Lombart Christophe </a>
 *
 */
public class ParentBeanConverterImpl extends AbstractBeanConverterImpl  implements BeanConverter
{

  private final static Log log = LogFactory.getLog(ParentBeanConverterImpl.class);

  public ParentBeanConverterImpl(Mapper mapper, ObjectConverter objectConverter, AtomicTypeConverterProvider
atomicTypeConverterProvider)
  {
    super(mapper, objectConverter, atomicTypeConverterProvider);
  }

  public void insert(Session session, Node parentNode, BeanDescriptor beanDescriptor, ClassDescriptor
beanClassDescriptor, Object object, ClassDescriptor parentClassDescriptor, Object parent)
      throws PersistenceException, RepositoryException,   JcrMappingException {

      // Add code to insert the object
  }

  public void update(Session session, Node parentNode, BeanDescriptor beanDescriptor, ClassDescriptor
beanClassDescriptor, Object object, ClassDescriptor parentClassDescriptor, Object parent)
      throws PersistenceException, RepositoryException,  JcrMappingException {

      // Add code to update the object
  }

  public Object getObject(Session session, Node parentNode, BeanDescriptor beanDescriptor,
ClassDescriptor beanClassDescriptor, Class beanClass, Object parent)
      throws PersistenceException, RepositoryException,JcrMappingException {

      // Add code to retrieve the object
  }

  public void remove(Session session, Node parentNode, BeanDescriptor beanDescriptor, ClassDescriptor
beanClassDescriptor, Object object, ClassDescriptor parentClassDescriptor, Object parent)
            throws PersistenceException,  RepositoryException, JcrMappingException {

      // Add the code to remove the object
  }

}
{code}


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