Implementing an Aggregate Object

In TopLink, two objects are related by aggregation if there is a one-to-one relationship between the objects and all the attributes of the second object can be retrieved from the same table(s) as the owning object. In the advanced tutorial, the EmploymentPeriod is an aggregate descriptor, and the period attribute is an aggregate object.

To map an aggregate object:

1. Select the EmploymentPeriod descriptor in the Navigator pane.

2. 
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   Click the Aggregate Descriptor button on the mapping toolbar. The descriptor's icon in the Navigator pane changes to an aggregate descriptor.

3. Map the startDate and EndDate attributes of the EmploymentPeriod as direct-to-field mappings.

   
   

   Note: The Database Field fields are disabled because the aggregate descriptor is not associated with a database table.

   
   

4. Expand the Employee descriptor in the Navigator pane.

5. Select the period attribute of the Employee descriptor.

6. 
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   Click the Aggregate Mapping button on the mapping toolbar.

   Figure B-38 Aggregate Mapping General Tab

   
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7. Use the Reference Descriptor drop-down list to choose the EmploymentPeriod aggregate descriptor.

8. Click the Fields tab.

   Figure B-39 Aggregate Mapping Fields Tab

   
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9. Use the Fields drop-down list to map each field as follows:

   • endDate – END_DATE

   • startDate – START_DATE

10. 
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    Click Save on the toolbar or choose File >  Save Project to save the project.