<p>看在基督的份上,不要用蒙克斯补丁。使用继承,这就是它的目的。在</p>
<p>只需让需要处理更多字段的插件扩展现有模型,然后使用多种技术中的一种来获得模型的最专业的类实例。为了实现这一点,我使用下面的类作为所有将以这种方式使用的类的mixin。在</p>
<pre><code>class Specializable(object):
@classmethod
def all_classes(selfclass):
""" Returns the class this is called on, plus its known subclasses """
subs = selfclass.__subclasses__()
subs.insert(0, selfclass)
return subs
def get_sub_instance(self):
""" Gets concrete instance of object of deepest subtype which has its ancestor link pointing to this object (depth first search behaviour). """
selftype = type(self)
for klass in selftype.__subclasses__():
this_ptr_name = klass._meta.get_ancestor_link(selftype).name
try:
sub = klass.objects.get(**{this_ptr_name: self})
subsub = sub.get_sub_instance()
if subsub: return subsub
else: return sub
except ObjectDoesNotExist:
pass
@classmethod
def new_with_translator(selfclazz, name):
def new(cls, *args, **kwargs):
selfclazz.create_subclass_translator(cls, install = name)
return models.Model.__new__(cls, *args, **kwargs)
return new
@classmethod
def create_subclass_translator(selfclazz, Baseclass, install=None):
""" Creates a classmethod object for installation on Baseclass,
which acts as a factory for instances of subclasses of Baseclass,
when called on that subclass. The factory takes as input an instance
of a subclass (old_instance), and a dictionary of properties with which
to initialise the new instance. It also installs the base class instance
of old_instance as the base instance for the new instance. All three will
share the same pk.
if install is set, this will also install the function on Baseclass under
that name if it does not have a property of that name. """
def create_from_other_instance(selfclass, old_instance, properties):
""" Creates an instance of this class using properties and old_instance.
In particular, it will try to re-use the superclass instance of old_instance.
properties should contain all of the fields for this class (but need not include the superclass values)
This *must* be called on a subclass of the baseclass - it will give odd results if called on the baseclass itself.
This will NOT delete old_instance and it will NOT SAVE the object created - the caller is responsible for
those things."""
if selfclass is Baseclass: raise TypeError("This method cannot be used on the base class")
ancestor_link = selfclass._meta.get_ancestor_link(Baseclass).name
properties.update({ancestor_link: getattr(old_instance,ancestor_link)})
for f in get_model_fields(Baseclass):
val = getattr(old_instance, f)
if val and not properties.get(f):
properties[f] = val
return selfclass(**properties)
new_method = classmethod(create_from_other_instance)
if install and not hasattr(Baseclass, install):
setattr(Baseclass, install, new_method)
return new_method
</code></pre>
<p>下面是它的使用示例,来自我的一些代码:</p>
^{pr2}$
<p>如您所见,<code>Specializable</code>类需要知道它们的方法可能被子类覆盖,并进行适当的编码。在</p>
<p>如果你的插件知道子类之间的关系,那么它可以使用一些技巧,比如在它知道的子类中搜索同一个模型id,在超类实例出现时得到相应的子类模型实例。在</p>