protected void buildAggregateMapKeyDescriptor() {
    RelationalDescriptor descriptor = new RelationalDescriptor();
    descriptor.descriptorIsAggregateCollection();
    descriptor.setJavaClass(AggregateMapKey.class);

    // Descriptor Properties.
    descriptor.setAlias("AggregateMapKey");

    // Mappings.
    DirectToFieldMapping keyMapping = new DirectToFieldMapping();
    keyMapping.setAttributeName("key");
    keyMapping.setFieldName("key->DIRECT");
    keyMapping.setAttributeClassification(Integer.class);
    descriptor.addMapping(keyMapping);

    addDescriptor(descriptor);
  }