如何确定模型类是 db 还是 ndb [英] How to find out if a model class is db or a ndb

问题描述

我创建了一个实用程序来交换或压缩所有实体为一种.但是我怎么知道使用的model_class是db.Model还是ndb.Model?

I created a utility to exchange or zip all the entities for a kind. But how can I find out if the model_class used is a db.Model or an ndb.Model?

def _encode_entity(self, entity):                                             

    if self.ndb :
        entity_dict = entity.to_dict()                                                     
        self.entity_eid = entity.key.id()
        entity_dict['NDB'] = True
    else :
        entity_dict = db.to_dict(entity)
        self.entity_eid = entity.key().name()
        entity_dict['NDB'] = False

    ....

现在我使用:

def queryKind(self):

    try :
        self.query = self.model_class.query()
        self.ndb = True
    except AttributeError :
        self.query = self.model_class.all()
        self.ndb = False
    return self.make(self._encode_entity)       # make a zip or a page

更新:我使用过的解决方案.另请参阅 Guido 的回答

UPDATE : The solution I have used. See also Guido's answer

self.kind = 'Greeting'
module = __import__('models', globals(), locals(), [self.kind], -1)
self.model_class = getattr(module, self.kind)
entity = self.model_class()

if isinstance(entity, ndb.Model): 
    self.ndb = True
    self.query = self.model_class.query()
elif isinstance(entity, db.Model): 
    self.ndb = False
    self.query = self.model_class.all()
else :
    raise ValueError('Failed to classify entities of kind : ' + self.kind)

推荐答案

如何导入 ndb 和 db，并测试实体是它们各自 Model 类的实例?

How about import ndb and db, and testing for the entity being an instance of their respective Model classes?

if isinstance(entity, ndb.Model):
    # Do it the NDB way.
elif isinstance(entity, db.Model):
    # Do it the db way.
else:
    # Fail.  Not an entity.

这篇关于如何确定模型类是 db 还是 ndb的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！