EclipseLink/DesignDocs/317962/Phase2.1

Phase 2 - Additional MOXy annotation/xml metadata support

This phase of development involves providing additional MOXy annotations and XML metadata support that will allow configuration similar to that of deployment XML

Annotations

The following MOXy XML metadata tags/annotations will be targeted in this phase:

MOXy Annotation	XML Metadata Tag	Package	Type	Field	Method
XmlProperties	xml-properties		X	X	X
XmlProperty	xml-property		X	X	X
XmlTransformation	xml-transformation			X	X
XmlReadTransformer	xml-read-transformer			X	X
XmlWriteTransformer	xml-write-transformer			X	X
XmlClassExtractor	xml-class-extractor		X

xml-properties

Purpose

The xml-properties element will be used as a grouping element to wrap one or more xml-property elements. See below for additional information and examples of use.

xml-property

Purpose

The xml-property element provides a means to set a property on a mapping or descriptor. Any annotations set on a property will be completely replaced by XML. Any annotations set on a type will be merged with XML, with XML taking precedence in the case of a conflict.

XML Schema

Since there can be multiple properties on a mapping or descriptor, and <xs:all> doesn't allow maxOccurs="unbounded", we will wrap xml-property in xml-properties. Following are the proposed schema changes:

<xs:element name="xml-properties" type="xml-properties" />
<xs:complexType name="xml-properties">
    <xs:sequence>
        <xs:element name="xml-property" minOccurs="0" maxOccurs="unbounded" >
            <xs:complexType>
                <xs:attribute name="name" type="xs:string" use="required" />
                <xs:attribute name="value" type="xs:string" use="required" />
                <xs:attribute name="value-type" type="xs:string" default="java.lang.String" />
            </xs:complexType>
        </xs:element>
    </xs:sequence>
</xs:complexType>

An element ref to the new global xml-properties element will be added to the following:

• java-type
• xml-any-attribute
• xml-attribute
• xml-any-element
• xml-element
• xml-elements
• xml-element-ref
• xml-element-refs
• xml-inverse-reference
• xml-value
• xml-transformation

Example: type-level xml-property

The following example will demonstrate how a type-level xml-property can be applied.

Setting xml-property on a type via EclipseLink XML metadata can be accomplished as follows:

<java-type name="org.example.Employee">
    <xml-properties>
        <xml-property name="identifier" value="101" value-type="Integer.class" />
        <xml-property name="isTrue" value="false" value-type="Boolean.class" />
    </xml-properties>
</java-type>

Example: property-level xml-property

The following example will demonstrate how a property-level xml-property can be applied.

Setting xml-property on a property via EclipseLink XML metadata can be accomplished as follows:

<java-type name="org.example.Employee">
    <java-attributes>
        <xml-element java-attribute="myelement">
            <xml-properties>
                <xml-property name="isAttribute" value="false" value-type="Boolean.class" />
                <xml-property name="comment" value="this is an element" />
            </xml-properties>
        </xml-element>
    </java-attributes>
</java-type>

Testing

Tests for xml-property and xml-properties will be added to the direct mapping test suite in the org.eclipse.persistence.testing.jaxb.externalizedmetadata.mappings.direct package.

xml-transformation

Purpose

The xml-transformation element is used to configure an org.eclipse.persistence.oxm.mappings.XMLTransformationMapping. Transformation mappings are used to create a custom mapping where one or more XML nodes can be used to create the object to be stored in a Java class's attribute.

XML Schema

Following is the proposed schema structure for xml-transformation:

<xs:element name="xml-transformation" substitutionGroup="java-attribute">
    <xs:complexType>
        <xs:complexContent>
            <xs:extension base="java-attribute">
                <xs:all>
                    <xs:element name="xml-access-methods" type="xml-access-methods" minOccurs="0"/>
                    <!-- xs:element name="xml-accessor-type" type="xml-access-type" minOccurs="0"/ -->
                    <xs:element name="xml-properties" minOccurs="0">
                        <xs:complexType>
                            <xs:sequence>
                                <xs:element ref="xml-property" minOccurs="0" maxOccurs="unbounded" />
                            </xs:sequence>
                        </xs:complexType>
                    </xs:element>
                    <xs:element name="xml-read-transformer">
                        <xs:complexType>
                            <xs:attribute name="method" type="xs:string" />
                            <xs:attribute name="transformer-class" type="xs:string" />
                        </xs:complexType>
                    </xs:element>
                    <xs:element name="xml-write-transformer" minOccurs="0" maxOccurs="unbounded">
                        <xs:complexType>
                            <xs:attribute name="method" type="xs:string" />
                            <xs:attribute name="xml-path" type="xs:string" />
                            <xs:attribute name="transformer-class" type="xs:string" />
                        </xs:complexType>
                    </xs:element>
                </xs:all>
                <xs:attribute name="attribute-type" type="xs:string" />
                <!-- xs:attribute name="fetch" type="orm:fetch-type"/ -->
                <xs:attribute name="mutable" type="xs:boolean" default="false"/>
                <xs:attribute name="name" type="xs:string" use="required"/>
                <xs:attribute name="optional" type="xs:boolean" default="false"/>
                <xs:attribute name="xml-accessor-type" type="xml-access-type" minOccurs="0" default="PUBLIC_MEMBER"/>
            </xs:extension>
        </xs:complexContent>
    </xs:complexType>
</xs:element>

Example

The following example will demonstrate how xml-transformation can be applied.

Setting xml-transformation via EclipseLink XML metadata can be accomplished as follows:

<java-type name="org.example.Employee">
    <java-attributes>
        <xml-transformation java-attribute="hours" optional="true">
            <xml-read-transformer transformer-class="org.example.NormalHoursTransformer" />
            <xml-write-transformer xml-path="normal-hours/start-time/text()" transformer-class="org.example.StartTimeTransformer"/>
            <xml-write-transformer xml-path="normal-hours/end-time/text()" transformer-class="org.example.EndTimeTransformer"/>
            <xml-access-methods get-method="getNormalHours" set-method="setNormalHours" />
        </xml-transformation>
    </java-attributes>
</java-type>

xml-class-extractor

Purpose

The xml-class-extractor element provides a means for complex inheritance support. A class extractor is registered with the descriptor to override the default inheritance mechanism. This allows for a user defined class indicator in place of providing an explicit class indicator field. The instance registered must extend the org.eclipse.persistence.descriptors.ClassExtractor class and implement the extractClassFromRow(Record, Session) method; this method is used to determine which class to instantiate when unmarshalling.

XML Schema

Following is the proposed schema structure for xml-class-extractor - a global element/complex type pair will be added, and a ref will be added to java-type:

<xs:element name="xml-class-extractor" type="xml-class-extractor" />
<xs:complexType name="xml-class-extractor">
    <xs:attribute name="class" type="xs:string" use="required"/>
</xs:complexType>

Annotation

The following is the proposed source code for the XmlClassExtractor annotation:

@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
public @interface XmlClassExtractor {
    /**
     * (Required) Defines the name of the class extractor that should be 
     * applied to this entity's descriptor.
     */
    Class value(); 
}

Example

The following example will demonstrate how the xml-class-extractor can be applied.

Setting xml-class-extractor via EclipseLink XML metadata can be accomplished as follows:

<java-type name="org.example.Person">
    <xml-class-extractor class="org.example.MyClassExtractor" />
</java-type>

Setting the Class Extractor via Annotations would be accomplished as follows:

org.example.Person.java

package org.example;
@XmlClassExtractor(MyClassExtactor.class)
class Person {
    String name;
}

org.example.Employee.java

package org.example;
 
class Employee extends Person {
    String id;
}

org.example.MyClassExtractor.java

package org.example;
 
class MyClassExtractor extends org.eclipse.persistence.descriptors.ClassExtractor {
    /**
     * This method simply returns Employee.class.  Typically, the class to be 
     * returned would be based on the given Record.
     */
    public static Class extractClassFromRow(Record databaseRow, Session session) {
        return Employee.class;
    }
}

Testing

A new suite of tests will be added in the org.eclipse.persistence.testing.jaxb.externalizedmetadata.xmlclassextractor package to test the XML metadata portion of this feature.

Decisions

This section lists decisions made. These are intended to document the resolution of open issues or constraints added to the project that are important.

Issue#	Description/Notes	Decision
1	xml-class-extraction-method	We will not provide support for setting a class extraction method name on the InheritancePolicy. Please refer to this bug for additional information.