Revision as of 13:22, 26 April 2011

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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>

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.

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

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);
   }
 
}

EclipseLink uses a set of default conversions to create a value for the Java attribute (in this case, xsd:decimal will be converted into a BigDecimal). You can override this behavior in Java code using the XMLUnionField method addConversion. For example, if you want your Java object to store shoeSize as a Float:

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

Special Schema Types	Special Schema Types	Binary Types
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