[python-chinese] Django model 的 manager 是如何工作的？

[jeff jie]

û´í£¬µÄÈ·ÓëContribute_to_classÕâ¸öº¯ÊýÓйء£¶ø¸Ã·½·¨±»Ö´Ðеĵط½Ç¡Ç¡ºÃÊÇModelµÄMateClassµÄ__new__()·½·¨ÀïÃ棺
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# Add Fields inherited from parents
        for parent in new_class._meta.parents:
            for field in parent._meta.fields:
                # Only add parent fields if they aren't defined for this
class.
                try:
                    new_class._meta.get_field(field.name)
                except FieldDoesNotExist:
                    field.contribute_to_class(new_class, field.name)

ħ·¨ÔÚÕâÀïʵÏÖ¡£ÒªÈ«²¿¿´¶®ÕâЩ´úÂë¿ÉÄܵò¹Ò»ÏÂPythonÔªÀà±à³Ì·½ÃæµÄ¿ÎÁË¡£ £º£©
http://www-128.ibm.com/developerworks/cn/linux/l-pymeta/index.html

ÔÚ07-12-3£¬book4e <book4e在gmail.com> дµÀ£º
>
> Äã¸æËßÎÒµÄÊǽáÂÛ£¬ÎÒÏëÖªµÀΪʲôÓÐÕâÑùµÄ½áÂÛ¡£
>
> return QuerySet(*self.model*) ÀïÃæµÄ model£¬Ò²¾ÍÊÇ PersonProfile£¬ÎÒÏëÊÇÔÚ
> PersonManager ³õʼ»¯µÄʱºò¾Í±»É趨ÁË£º
>
> objects = PersonManager()
>
> ÄÇô PersonManager ÊÇÈçºÎ¸ÐÖª PersonProfile µÄ£¬ÊÇ·ñºÍÏÂÃæµÄ´úÂëÓйأ¿
>
>     def __init__(self):
>         super(Manager, self).__init__()
>         # Increase the creation counter, and save our local copy.
>         self.creation_counter = Manager.creation_counter
>         Manager.creation_counter += 1
>         self.model = None
>
>     def contribute_to_class(self, model, name):
>         # TODO: Use weakref because of possible memory leak / circular
> reference.
>         self.model = model
>         setattr(model, name, ManagerDescriptor(self))
>         if not hasattr(model, '_default_manager') or self.creation_counter< model._default_manager.creation_counter:
>             model._default_manager = self
>
> ËƺõÓë contribute_to_class ºÜÓйØϵ£¬µ«ÎÒûÓп´¶®Õâ¶Î´úÂëµÄÒâ˼£¬Ò²Ã»ÕÒµ½ËüÊǺÎʱ±»µ÷Óõġ£Äܲ»ÄܾßÌå½²½²£¿
>
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