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Difference between revisions of "EclipseLink/UserGuide/MOXy/Simple Values/Special Schema Types/Unions"

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{{EclipseLink_UserGuide
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Please see http://www.eclipse.org/eclipselink/documentation/2.4/moxy/special_schema_types002.htm
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}}
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=Mapping to a Union Field=
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The following XML schema and class diagram show a typical use of an XML Schema Union:
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<source lang="xml">
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<?xml version="1.0" encoding="UTF-8"?>
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<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema">
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    <xsd:element name="customer" type="customer-type" />
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    <xsd:complexType name="customer-type">
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        <xsd:sequence>
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            <xsd:element name="shoe-size" type="size-type" />
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        </xsd:sequence>
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    </xsd:complexType>
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    <xsd:simpleType name="size-type">
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        <xsd:union memberTypes="xsd:decimal xsd:string" />
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    </xsd:simpleType>
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</xsd:schema>
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</source>
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[[Image:dxmuc.gif]]<br><br>
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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.
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[[Image:dxmuv.gif]]<br><br>
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In a second example document, the value "M" is not a valid '''xsd:decimal''' type, so the next union type is tried, '''xsd:string'''.
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[[Image:dxmuvs.gif]]<br><br>
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== Example ==
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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.
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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.
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<source lang="java">
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package example;
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import javax.xml.bind.annotation.*;
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import org.eclipse.persistence.oxm.annotations.*;
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@XmlRootElement
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@XmlAccessorType(XmlAccessType.FIELD)
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@XmlCustomizer(CustomerCustomizer.class)
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public class Customer {
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  @XmlTransient
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  private Object shoeSize;
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  ...
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}
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</source>
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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()''':
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<source lang="java">
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package example;
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import org.eclipse.persistence.config.DescriptorCustomizer;
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import org.eclipse.persistence.descriptors.ClassDescriptor;
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import org.eclipse.persistence.oxm.*;
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public class CustomerCustomizer implements DescriptorCustomizer {
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  @Override
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  public void customize(ClassDescriptor descriptor) throws Exception {
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      XMLDirectMapping shoeSizeMapping = new XMLDirectMapping();
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      shoeSizeMapping.setAttributeName("shoeSize");
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      XMLUnionField shoeSizeField = new XMLUnionField();
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      shoeSizeField.setXPath("shoe-size/text()");
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      shoeSizeField.addSchemaType(XMLConstants.DECIMAL_QNAME);
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      shoeSizeField.addSchemaType(XMLConstants.STRING_QNAME);
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      shoeSizeMapping.setField(shoeSizeField);
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      descriptor.addMapping(shoeSizeMapping);
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  }
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}
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</source>
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== Conversion Order ==
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The order of the calls to '''addSchemaType()''' is important; when converting an XML value into Java, EclipseLink will attempt the conversions in the order that they were added to the field, and return as soon as a successful conversion is made.  For example, when unmarshalling a '''shoeSize''' of "10.5":
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<source lang="java">
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...
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shoeSizeField.addSchemaType(XMLConstants.DECIMAL_QNAME);
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shoeSizeField.addSchemaType(XMLConstants.STRING_QNAME);
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...
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</source>
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A '''BigDecimal''' will be created to store the value.  If, however, your '''XMLUnionField''' was set up like this:
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<source lang="java">
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...
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shoeSizeField.addSchemaType(XMLConstants.STRING_QNAME);
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shoeSizeField.addSchemaType(XMLConstants.DECIMAL_QNAME);
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...
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</source>
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The '''shoeSize''' value will be a String ("10.5").
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== Customizing Conversion Classes ==
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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''':
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<source lang="java">
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shoeSizeField.addConversion(XMLConstants.DECIMAL_QNAME, Float.class);
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</source>
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Latest revision as of 10:19, 8 November 2012

Please see http://www.eclipse.org/eclipselink/documentation/2.4/moxy/special_schema_types002.htm