Working with Array Mappings

In an object-relational data-model, structures can contain arrays (collections of other data types). These arrays can contain primitive data types or collections of other structures. OracleAS TopLink stores the arrays with their parent structure in the same table.

All elements in the array must be the same data type. The number of elements in an array controls the size of the array. An Oracle database allows arrays of variable sizes (called Varrays).

Oracle8i offers two collection types:

Varray – Used to represent a collection of primitive data or aggregate structures.
Nested table – Similar to varrays except they store information in a separate table from the parent structure's table

OracleAS TopLink supports arrays of primitive data through the ArrayMapping class. This is similar to DirectCollectionMapping – it represents a collection of primitives in Java. However, the ArrayMapping class does not require an additional table to store the values in the collection.

OracleAS TopLink supports arrays of aggregate structures through the ObjectArrayMaping class.

OracleAS TopLink supports nested tables through the NestedTableMapping class.

Implementing Array Mappings in Java

Array mappings are instances of the ArrayMapping class. You must associate this mapping to an attribute in the parent class. OracleAS TopLink requires the following elements for an array mapping:

Attribute being mapped – Set by sending the setAttributeName( ) message.
Field being mapped – Set by sending the setFieldName( ) message.
Name of the array – Set by sending the setStructureName( ) message.

Table 7-1 summarizes all array mapping properties:

Example 7-1 Array Mapping

The following code example illustrates creating an array mapping for the Employee source class and registering it with the descriptor

// Create a new mapping and register it with the source descriptor.
ArrayMapping arrayMapping = new ArrayMapping();
arrayMapping.setAttributeName("responsibilities");
arrayMapping.setStructureName("Responsibilities_t");
arrayMapping.setFieldName("RESPONSIBILITIES");
descriptor.addMapping(arrayMapping);

Reference

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

Table 7-1 Properties for ArrayMapping methods

Property	Default	Method Names
* Required property
Attribute to be mapped *	not applicable	`setAttributeName(String name)`
Set parent class *	not applicable	`setReferenceClass(Class referenceClass)`
User-defined data type *	not applicable	`setStructureName(String Structurename)`
Field to be mapped *	not applicable	`setFieldName(String fieldName)`
Method access	direct access	`setGetMethodName(String name)` `setSetMethodName(String name)`
Read only	read / write	`readWrite()` `readOnly()` `setIsReadOnly(boolean readOnly)`