Sets the columns that this schema uses.
        
        :param      columns     | [<orb.Column>, ..]

def setColumns(self, columns):
        """
        Sets the columns that this schema uses.
        
        :param      columns     | [<orb.Column>, ..]
        """
        self.__columns = {}
        for name, column in columns.items():
            self.__columns[name] = column
            column.setSchema(self)