code: def _find_parameter(cls, dct):
          '''Search for the 'key=True' case, and confirm no more than one parameter has that property.'''
  
          num_found = 0
          field = None
  
          for key, val in dct.iteritems():
              if isinstance(val, DataType) and val.is_key:
                  field = key
                  num_found += 1
  
          if num_found > 1:
              raise SetupError(502)
          elif num_found == 0:
              return False
  
          dct['_cbs_key_field'] = field
          dct['key'] = cls._build_prop(field)
          return Truf _find_parameter(cls, dct):
          '''Search for the 'key=True' case, and confirm no more than one parameter has that property.'''
  
          num_found = 0
          field = None
  
          for key, val in dct.iteritems():
              if isinstance(val, DataType) and val.is_key:
                  field = key
                  num_found += 1
  
          if num_found > 1:
              raise SetupError(502)
          elif num_found == 0:
              return False
  
          dct['_cbs_key_field'] = field
          dct['key'] = cls._build_prop(field)
          return True
docs: Search for the 'key=True' case, and confirm no more than one parameter has that property.