docs: def _construct_columns(self, column_map):
          
          ''' a helper method for constructing the column objects for a table object '''
          
          from sqlalchemy import Column, String, Boolean, Integer, Float, Binary 
      
          column_args = []
          for key, value in column_map.items():
              record_key = value[0]
              datatype = value[1]
              max_length = value[2]
              if record_key == 'id':
                  if datatype in ('string', 'float', 'integer'):
                      if datatype == 'string':
                          if max_length:
                              column_args.insert(0, Column(record_key, String(max_length), primary_key=True))
                          else:
                              column_args.insert(0, Column(record_key, String, primary_key=True))
                      elif datatype == 'float':
                          column_args.insert(0, Column(record_key, Float, primary_key=True))
                      elif datatype == 'integer':
                          column_args.insert(0, Column(record_key, Integer, primary_key=True))
                  else:
                      raise ValueError('Field "id" in record_schema must be a string, float or integer.')
              else:
                  if datatype == 'boolean':
                      column_args.append(Column(record_key, Boolean))
                  elif datatype == 'string':
                      if max_length:
                          column_args.append(Column(record_key, String(max_length)))
                      else:
                          column_args.append(Column(record_key, String))
                  elif datatype == 'float':
                      column_args.append(Column(record_key, Float))
                  elif datatype == 'integer':
                      column_args.append(Column(record_key, Integer))
                  elif datatype == 'list':
                      column_args.append(Column(record_key, Binary))
          
          return column_args