关于Django外键赋值问题详解

 class Article(models.Model): title = models.CharField(max_length=1024, default='') ... def __str__(self): return 'Article pk:%d %s' % (self.pk, self.title[:30]) class ArticleContent(models.Model): article = cached_fields.OneToOneField(Article) ...

 In [44]: ac = ArticleContent.objects.get(article_id=14269) In [45]: ac.article_id Out[45]: 14269 In [46]: ac.article_id = 14266 In [47]: ac.save() In [48]: ac.article Out[48]:  In [49]: ac.article.pk Out[49]: 14266

 django/db/models/fields/related_descriptors.py def __get__(self, instance, cls=None): """ Get the related instance through the forward relation. With the example above, when getting ``child.parent``: - ``self`` is the descriptor managing the ``parent`` attribute - ``instance`` is the ``child`` instance - ``cls`` is the ``Child`` class (we don't need it) """ if instance is None: return self # The related instance is loaded from the database and then cached in # the attribute defined in self.cache_name. It can also be pre-cached # by the reverse accessor (ReverseOneToOneDescriptor). try: rel_obj = getattr(instance, self.cache_name) except AttributeError: val = self.field.get_local_related_value(instance) if None in val: rel_obj = None else: qs = self.get_queryset(instance=instance) qs = qs.filter(self.field.get_reverse_related_filter(instance)) # Assuming the database enforces foreign keys, this won't fail. rel_obj = qs.get() # If this is a one-to-one relation, set the reverse accessor # cache on the related object to the current instance to avoid # an extra SQL query if it's accessed later on. if not self.field.remote_field.multiple: setattr(rel_obj, self.field.remote_field.get_cache_name(), instance) setattr(instance, self.cache_name, rel_obj) if rel_obj is None and not self.field.null: raise self.RelatedObjectDoesNotExist( "%s has no %s." % (self.field.model.__name__, self.field.name) ) else: return rel_obj