Working with Reference Mappings

In an object-relational data-model, structures reference each other through refs—not through foreign keys (as in a traditional data-model). Refs are based on the target structure's ObjectID.

OracleAS TopLink supports refs through the ReferenceMapping class. They represent an object reference in Java, similar to a OneToOneMapping. However, the reference mapping does not require foreign key information.

Implementing Reference Mappings in Java

Reference mappings are instances of the ReferenceMapping class. You must associate this mapping to an attribute in the source class. OracleAS TopLink requires the following elements for a reference mapping:

• Attribute being mapped – Set by sending the setAttributeName( ) message.

• Field being mapped – Set by sending the setFieldName( ) message.

• Target class – Set by sending the setReferenceClass( ) message.

Use the optional setGetMethodName( ) and setSetMethodName( ) messages to access the attribute through user-defined methods rather than directly. See "Specifying Direct Access and Method Access" on page 4-71 for more information.

Table 7–4 summarizes all reference mapping properties.

Example 7-4 Reference Mapping

The following code example illustrates creating a reference mapping for the Employee source class and registering it with the descriptor.

// Create a new mapping and register it with the source descriptor.
ReferenceMapping refrenceMapping = new ReferenceMapping();
referenceMapping.setAttributeName(ÒmanagerÓ);
referenceMapping.setReferenceClass(Employee.class);
referenceMapping.setFieldName("MANAGER");
descriptor.addMapping(refrenceMapping);

Reference

The following table summarizes all reference mapping properties. In the Method Names column, arguments are bold, methods are not.

Table 7-4 Properties for ReferenceMapping Methods

Property	Default	Method Names
* Required property
Attribute to be mapped *	not applicable	setAttributeName(String name)
Set parent class *	not applicable	setReferenceClass(Class aClass)
Field to be mapped *	not applicable	setFieldName(String fieldName)
Method access	direct access	setGetMethodName(String name) setSetMethodName(String name)
Indirection	use indirection	useBasicIndirection() dontUseIndirection()
Privately owned relationship	independent	independentRelationship() privateOwnedRelationship() setIsPrivateOwned(boolean isPrivateOwned)
Read only	read / write	readWrite() readOnly() setIsReadOnly(boolean readOnly)