EclipseLink/DesignDocs/293925/MOXyExtensions/XMLDirectMapping

XMLDirectMapping

Requirements

Provide support for XML direct mappings.

The following structures are to be extended to support XML direct mapping configuration:

• xml-attribute
• xml-element
• xml-value

Path-based mappings must be supported. Design notes are located here.

The following should be configurable:

• Positional Mappings
• Read only (boolean)
• Write only (boolean)
• CDATA (boolean)
• Converters
• Default null value
• Null policy
• Get/set method names

Design

Basic XML direct mapping support

We will use the xml-attribute, xml-element and xml-value structures to support direct mappings. For example, the following XML metadata snippet would be used to setup a direct mapping for an empId attribute:

<xml-attribute java-attribute="empId" />

If empId was to be mapped to id, then the following would be used:

<xml-attribute java-attribute="empId" name="id" />

The same example mapped to an id element:

<xml-element java-attribute="empId" name="id" />

The same example mapped to a simple type:

<xml-value java-attribute="empId" />

Example

The following example will demonstrate how to configure XML direct mappings via XML metadata.

org.example.Employee.java

package org.example;
 
public class Employee {
    public int empId;
    public String firstName;
    public String lastName;
    public String projectName;
}

Deployment XML

<class-mapping-descriptor xsi:type="xml-class-mapping-descriptor">
    <alias>Employee</alias>
    <attribute-mappings>
        <attribute-mapping xsi:type="xml-direct-mapping">
           <attribute-name>empId</attribute-name>
           <field name="@id" xsi:type="node"/>
        </attribute-mapping>
        <attribute-mapping xsi:type="xml-direct-mapping">
           <attribute-name>firstName</attribute-name>
           <field name="personal-info/first-name/text()" xsi:type="node"/>
        </attribute-mapping>
        <attribute-mapping xsi:type="xml-direct-mapping">
           <attribute-name>lastName</attribute-name>
           <field name="personal-info/last-name/text()" xsi:type="node"/>
        </attribute-mapping>
        <attribute-mapping xsi:type="xml-direct-mapping">
            <attribute-name>mgrId</attribute-name>
            <field name="projects/prj:project/@managerId" xsi:type="node"/>
        </attribute-mapping>
        <attribute-mapping xsi:type="xml-direct-mapping">
           <attribute-name>projectName</attribute-name>
           <field name="projects/prj:project/text()" xsi:type="node"/>
        </attribute-mapping>
    <attribute-mappings>
    <descriptor-type>aggregate</descriptor-type>
    <default-root-element>employee</default-root-element>
    <default-root-element-field name="employee" xsi:type="node"/>
    <namespace-resolver>
        <namespaces>
            <namespace>
                <prefix>prj</prefix>
                <namespace-uri>http://www.example.com/projects</namespace-uri>
            </namespace>
        </namespaces>
        <default-namespace-uri>http://www.example.com/employees</default-namespace-uri>
    </namespace-resolver>
</class-mapping-descriptor>

XML Instance Document

<?xml version="1.0" encoding="UTF-8"?>
<employee id="66" xmlns="http://www.example.com/employees" xmlns:prj="http://www.example.com/projects">
    <personal-info>
        <first-name>Joe</first-name>
        <last-name>Black</last-name>
    </personal-info>
    <projects>
        <prj:project managerId="99">XML External Metadata Support</prj:project>
    </projects>
</employee>

org/example/eclipselink-oxm.xml

This XML file demonstrates configuring XML direct mappings on the "org.example.Employee" class.

<?xml version="1.0" encoding="US-ASCII"?>
<xml-bindings xmlns="http://www.eclipse.org/eclipselink/xsds/persistence/oxm">
    <xml-schema namespace="http://www.example.com/employees">
        <xml-ns namespace-uri="http://www.example.com/projects" prefix="prj"/>
    </xml-schema>
    <java-types>
        <java-type name="org.example.Employee">
            <xml-root-element name="employee" />
            <java-attributes>
                <xml-attribute java-attribute="empId" name="id" />
                <xml-element java-attribute="firstName" name="first-name">
                    <xml-element-wrapper name="personal-info" />
                </xml-element>
                <xml-element java-attribute="lastName" name="last-name" >
                    <xml-element-wrapper name="personal-info" />
                </xml-element>
                <xml-attribute java-attribute="mgrId" name="managerId" >
                    <xml-element-wrapper name="projects/prj:project" />
                </xml-attribute>
                <xml-element java-attribute="projectName" name="project" namespace="http://www.example.com/projects" >
                    <xml-element-wrapper name="projects" />
                </xml-element>
            </java-attributes>
        </java-type>
    </java-types>
</xml-bindings>

Open Issues

This section lists the open issues that are still pending that must be decided prior to fully implementing this project's requirements.

Issue#	Owner	Description/Notes
1	D.McCann	Two possible ways to allow a path-based mapping to be configured are being considered: xml-attribute/xml-element or xml-element-wrapper. Which is preferred? Design note are located here.
2	D.McCann	Three possible ways to set the path for a mapping are being considered: name overload vs. xpath vs. name + grouping-element. Which is preferred? Design notes are located here.
3	D.McCann	What is the expected behavior when namespace is set on an xml-element-wrapper that has a path set?
4	D.McCann	What is the expected behavior when required is set on an xml-element-wrapper that has a path set?
5	D.McCann	What is the expected behavior when nillable is set on an xml-element-wrapper that has a path set?
6	D.McCann	How can we support positional mappings?
7	D.McCann	What will the schema look like WRT converters?

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	Two possible ways to allow a path-based mapping to be configured are being considered: xml-attribute/xml-element or xml-element-wrapper	xml-element-wrapper will be extended to handle multi-level paths, and enabled for use with xml-attribute and single-valued properties.
2	Three possible ways to set the path for a mapping are being considered: name overload vs. xpath vs. name + grouping-element	name will be overloaded.
3	What is the expected behavior when namespace is set on an xml-element-wrapper that has a path set?	If namespace is set, it will be applied to any path element that is not prefixed.
4	What is the expected behavior when required is set on an xml-element-wrapper that has a path set?	If required is set, it will be applied to the last element in the path.
5	What is the expected behavior when nillable is set on an xml-element-wrapper that has a path set?	If nillable is set, it will be applied to the last element in the path.
6	How can we support positional mappings?	Positional mappings will be supported by overloading the name attribute on xml-element / xml-value.

Future Considerations

During the research for this project the following items were identified as out of scope but are captured here as potential future enhancements. If agreed upon during the review process these should be logged in the bug system.

• For issue #2 above, it may be useful to add an additional attribute such that users who do not wish use the name attribute in a non-standard way are able to set a multi-level path.