code: def setup_fields_processors(config, model_cls, schema):
      
      properties = schema.get('properties', {})
      for field_name, props in properties.items():
          if not props:
              continue
  
          processors = props.get('_processors')
          backref_processors = props.get('_backref_processors')
  
          if processors:
              processors = [resolve_to_callable(val) for val in processors]
              setup_kwargs = {'model': model_cls, 'field': field_name}
              config.add_field_processors(processors, **setup_kwargs)
  
          if backref_processors:
              db_settings = props.get('_db_settings', {})
              is_relationship = db_settings.get('type') == 'relationship'
              document = db_settings.get('document')
              backref_name = db_settings.get('backref_name')
              if not (is_relationship and document and backref_name):
                  continue
  
              backref_processors = [
                  resolve_to_callable(val) for val in backref_processors]
              setup_kwargs = {
                  'model': engine.get_document_cls(document),
                  'field': backref_name
              }
              config.add_field_processors(
                  backref_processors, **setup_kwargs)
docs: Set up model fields' processors.
  
      :param config: Pyramid Configurator instance.
      :param model_cls: Model class for field of which processors should be
          set up.
      :param schema: Dict of model JSON schema.