code: def _resource_index(self, resource):
          
          datasource = self.get_datasource(resource)
          indexes = self._resource_config(resource, 'INDEXES') or {}
          default_index = self._resource_config(resource, 'INDEX')
          return indexes.get(datasource[0], default_index)
docs: Get index for given resource.
  
          by default it will be `self.index`, but it can be overriden via app.config
  
          :param resource: resource name