code: def load(self, data):
          
          objs = {}
          for mapper in self.entities:
              objs[mapper.name] = mapper.load(self.loader, data)
  
          for mapper in self.relations:
              objs[mapper.name] = mapper.load(self.loader, data, objs)
docs: Load a single row of data and convert it into entities and
          relations.