Oracle® Application Server TopLink Mapping Workbench User's Guide
10g Release 2 (10.1.2) Part No. B15900-01 |
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Nested table types model an unordered set of elements. These elements may be built-in or user-defined types. You can view a nested table as a single-column table or, if the nested table is an object type, as a muticolumn table (with a column for each attribute of the object type).
Typically, nested tables represent a one-to-many or many-to-many relationship of references to another independent structure. They support querying and joining better than Varrays that are inlined to the parent table.
OracleAS TopLink supports nested table through the NestedTableMapping
class. They represent a collection of object references in Java, similar to a OneToManyMapping
or ManyToManyMapping
. However, the nested table mapping does not require foreign key information (as with a one-to-many mapping) or the relational table (as with a many-to-many mapping).
Nested table mappings are instances of the NestedTableMapping
class. This mapping is associated to an attribute in the parent class. The following elements are required for a nested table mapping to be viable:
The attribute being mapped, which is set by sending the setAttributeName()
message
The field being mapped, which is set by sending the setFieldName()
message
The name of the array structure, which is set by sending the setStructureName()
message
Use the optional setGetMethodName()
and setSetMethodName()
messages to allow OracleAS TopLink 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 7–5 summarizes all nested table mapping properties.
Example 7-5 Nested Table
The following code example illustrates creating a nested table mapping for the Insurance source class and registering it with the descriptor.
// Create a new mapping and register it with the source descriptor. NestedTableMapping policiesMapping = new NestedTableMapping(); policiesMapping.setAttributeName("policies"); policiesMapping.setGetMethodName("getPolicies"); policiesMapping.setSetMethodName("setPolicies"); policiesMapping.setReferenceClass(Policy.class); policiesMapping.dontUseIndirection(); policiesMapping.setStructureName("POLICIES_TYPE"); policiesMapping.setFieldName("POLICIES"); policiesMapping.privateOwnedRelationship(); policiesMapping.setSelectionSQLString("select p.* from policyHolders ph, table(ph.policies) t, policies p where ph.ssn=#SSN and ref(p) = value(t)"); descriptor.addMapping(policiesMapping);
The following table summarizes all nested table mapping properties. In the Method Names column, arguments are bold, methods are not.
Table 7-5 Properties for NestedTableMapping Methods
Property | Default | Method Names |
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* Required property |
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Attribute to be mapped * | not applicable | setAttributeName (String name)
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Set parent class * | not applicable | setReferenceClass (Class referenceClass)
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User-defined data type * | not applicable | setStructureName (String structureName)
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Field to be mapped * | not applicable | setFieldName (String fieldName)
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Method access | direct access | setGetMethodName (String name)
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Indirection | use indirection | useIndirection ()
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Privately owned relationship | independent | independentRelationship ()
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Read only | read / write | readWrite ()
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