EclipseLink/UserGuide/MOXy/Simple Values/Special Schema Types/Unions

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Contents


Mapping to a Union Field

The following XML schema and class diagram show a typical use of an XML Schema Union:

<?xml version="1.0" encoding="UTF-8"?>
<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema">
    <xsd:element name="customer" type="customer-type" />
    <xsd:complexType name="customer-type">
        <xsd:sequence>
            <xsd:element name="shoe-size" type="size-type" />
        </xsd:sequence>
    </xsd:complexType>
    <xsd:simpleType name="size-type">
        <xsd:union memberTypes="xsd:decimal xsd:string" />
    </xsd:simpleType>
</xsd:schema>

Dxmuc.gif

The figure below illustrates a mapping to a union field in an XML document that conforms to the example schema. When EclipseLink unmarshalls the XML document, it tries each of the union types until it can make a successful conversion. The first schema type in the union is xsd:decimal. Because "10.5" is a valid decimal, EclipseLink converts the value to the appropriate type. If the Object attribute is specific enough to trigger an appropriate value, EclipseLink will use that type instead. Otherwise, EclipseLink uses a default (in this case BigDecimal). You can override this behavior in Java code.

Dxmuv.gif

In a second example document, the value "M" is not a valid xsd:decimal type, so the next union type is tried, xsd:string.

Dxmuvs.gif

Example

Currently, EclipseLink does not support the mapping of Unions using Annotations or OXM Metadata. However, an EclipseLink XML Customizer can be used to create the mapping.

First, we annotate the shoeSize attribute with @XmlTransient, to avoid automatically generating a mapping for it. We also include an @XmlCustomizer annotation; the CustomerCustomizer class will create the Union mapping in code.

package example;
 
import javax.xml.bind.annotation.*;
import org.eclipse.persistence.oxm.annotations.*;
 
@XmlRootElement
@XmlAccessorType(XmlAccessType.FIELD)
@XmlCustomizer(EmployeeCustomizer.class)
public class Customer {
   @XmlTransient
   private Object shoeSize;
 
   ...
}


The CustomerCustomizer class can be used to manually add a mapping to the shoeSize attribute. Here, an XMLUnionField is configured on the mapping, and the possible Union member types are added by calling addSchemaType():

package example;
 
import org.eclipse.persistence.config.DescriptorCustomizer;
import org.eclipse.persistence.descriptors.ClassDescriptor;
import org.eclipse.persistence.oxm.*;
 
public class CustomerCustomizer implements DescriptorCustomizer {
 
   @Override
   public void customize(ClassDescriptor descriptor) throws Exception {
      XMLDirectMapping shoeSizeMapping = new XMLDirectMapping();
      shoeSizeMapping.setAttributeName("shoeSize");
 
      XMLUnionField shoeSizeField = new XMLUnionField();
      shoeSizeField.setXPath("shoe-size/text()");
      shoeSizeField.addSchemaType(XMLConstants.DECIMAL_QNAME);
      shoeSizeField.addSchemaType(XMLConstants.STRING_QNAME);
 
      shoeSizeMapping.setField(shoeSizeField);
 
      descriptor.addMapping(shoeSizeMapping);
   }
 
}


To override the default conversion, use the XMLUnionField method addConversion:

   shoeSizeField.addConversion(XMLConstants.DECIMAL_QNAME, Float.class);


Mapping to a Union of Lists

EclipseLink also supports mapping to lists of Unions, as demonstrated in the following schema:

<?xml version="1.0" encoding="UTF-8"?>
<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema">
   <xsd:element name="employee" type="employee-type"/>   
 
   <xsd:complexType name="employee-type">
      <xsd:sequence>
         <xsd:element name="vacation" type="union-of-lists"/>
      </xsd:sequence>
   </xsd:complexType>
 
   <xsd:simpleType name="union-of-lists">
      <xsd:union memberTypes="xsd:double">
         <xsd:simpleType>
            <xsd:list itemType="xsd:date"/>
         </xsd:simpleType>
 
         <xsd:simpleType>
            <xsd:list itemType="xsd:integer"/>
         </xsd:simpleType>
      </xsd:union>
   </xsd:simpleType>
</xsd:schema>

Dxuofl.gif

Note that in this example, valid XML documents contain either a single xsd:double value, a list of xsd:date values, or a list of xsd:integer values.

This can be configured as follows:

package example;
 
import org.eclipse.persistence.config.DescriptorCustomizer;
import org.eclipse.persistence.descriptors.ClassDescriptor;
import org.eclipse.persistence.oxm.*;
 
public class VacationCustomizer implements DescriptorCustomizer {
 
   @Override
   public void customize(ClassDescriptor descriptor) throws Exception {
      XMLDirectMapping shoeSizeMapping = new XMLDirectMapping();
      shoeSizeMapping.setAttributeName("shoeSize");
 
      XMLUnionField shoeSizeField = new XMLUnionField();
      shoeSizeField.setXPath("shoeSize/text()");
      shoeSizeField.addSchemaType(XMLConstants.DECIMAL_QNAME);
      shoeSizeField.addSchemaType(XMLConstants.STRING_QNAME);
 
      shoeSizeMapping.setField(shoeSizeField);
 
      descriptor.addMapping(shoeSizeMapping);
   }
 
}


Mapping to a Union of Unions

Given the XML schema in the Schema for XML Direct Mapping to a Union of Unions example, the Java Class for XML Direct Mapping to a Union of Unions figure illustrates a Java class that can be mapped to a corresponding XML document. The Java for XML Direct Mapping to a Union of Unions example shows how to configure this mapping in Java.


Schema for XML Direct Mapping to a Union of Unions

<?xml version="1.0" encoding="UTF-8"?>
<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema">
    <xsd:element name="vacation" type="unionOfUnions"/>
    <xsd:simpleType name="unionOfUnions">
        <xsd:union>

            <xsd:simpleType>
                <xsd:union>
                    <xsd:simpleType>
                        <xsd:list itemType="xsd:date"/>
                    </xsd:simpleType>
                    <xsd:simpleType>

                        <xsd:list itemType="xsd:integer"/>
                    </xsd:simpleType>
                </xsd:union>
            </xsd:simpleType>
            <xsd:simpleType>
                <xsd:union>

                    <xsd:simpleType>
                        <xsd:list itemType="xsd:string"/>
                    </xsd:simpleType>
                    <xsd:simpleType>
                        <xsd:list itemType="xsd:float"/>
                    </xsd:simpleType>

                </xsd:union>
            </xsd:simpleType>
        </xsd:union>
    </xsd:simpleType>
</xsd:schema>


Java Class for XML Direct Mapping to a Union of Unions

Dxuofu.gif


Java for XML Direct Mapping to a Union of Unions

XMLDirectMapping vacationMapping = new XMLDirectMapping();
vacationMapping.setAttributeName("vacation");
XMLUnionField vacationField = new XMLUnionField();
vacationField.setXPath("vacation/text()");
vacationField.addSchemaType(XMLConstants.DATE_QNAME);
vacationField.addSchemaType(XMLConstants.INTEGER_QNAME);
vacationField.addSchemaType(XMLConstants.STRING_QNAME);
vacationField.addSchemaType(XMLConstants.FLOAT_QNAME);
vacationMapping.setField(vacationField);


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