The primary purpose of this function is to store the sql field list
        and the depth to which we process.

def process_fields(self, field_names, depth):
        '''
        The primary purpose of this function is to store the sql field list
        and the depth to which we process.
        '''
        # List of field names in correct order.
        self.field_names = field_names
        # number of fields.
        self.num_fields = len(field_names)
        # Constrain depth.
        if (depth == 0) or (depth >= self.num_fields):
            self.depth = self.num_fields - 1
        else:
            self.depth = depth