code: final Set<String> getPrimaryColumnNames() {
  		final List<DBColumn> primaryKeyColumnList = getPrimaryKeyColumnList();
  		final Set<String> primaryKeyColumnNameSet = new LinkedHashSet<String>();
  		for (DBColumn col : primaryKeyColumnList) {
  
  			primaryKeyColumnNameSet.add(col.columnName());
  		}
  		return primaryKeyColumnNameSet;
  	}
docs: Returns Set of primary key column name of model class
  
  @return