code: final List<Field> getPrimaryKeyFieldList() {
  
  		final List<Field> fieldList = new ArrayList<Field>();
  
  		final Set<String> columnNameSet = getAllColumnNames();
  
  		for (String columnName : columnNameSet) {
  
  			final D6ModelClassFieldInfo fieldInfo = getFieldInfo(columnName);
  
  			final Field field = fieldInfo.field;
  
  			final DBColumn dbColumn = field.getAnnotation(DBColumn.class);
  
  			if (dbColumn.isPrimaryKey()) {
  
  				fieldList.add(field);
  			}
  		}
  
  		return fieldList;
  	}
docs: get primary key field of model class
  
  @return