87 lines
3.2 KiB
Python
87 lines
3.2 KiB
Python
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# -*- coding: utf-8 -*-
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class SignalConnectMetaClass(type):
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"""
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Metaclass to connect the children of a base class to a Django signal.
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Classes must have a signal argument and a get_dispatch_uid classmethod.
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The signal argument must be the Django signal the class should be
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connected to. The get_dispatch_uid classmethod must return a unique
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value for each child class and None for base classes which will not be
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connected.
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The classmethod get_all_objects is added as get_all classmethod to every
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class using this metaclass. Calling this on a base class or on child
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classes will retrieve all connected children, on instance for each child
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class. These instances will have a check_permission method which
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returns True by default. You can override this method to return False
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on runtime if you want to filter some children.
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Example:
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class Base(object):
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__metaclass__ = SignalConnectMetaClass
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signal = django.dispatch.Signal()
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@classmethod
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def get_dispatch_uid(cls):
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if not cls.__name__ == 'Base':
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return cls.__name__
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class Child(Base):
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def __init__(self, **kwargs):
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pass
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child = Base.get_all(request)[0]
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assert Child == type(child)
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"""
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def __new__(metaclass, class_name, class_parents, class_attributes):
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"""
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Creates the class and connects it to the signal if so.
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"""
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class_attributes['get_all'] = get_all_objects
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new_class = super(SignalConnectMetaClass, metaclass).__new__(
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metaclass, class_name, class_parents, class_attributes)
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try:
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dispatch_uid = new_class.get_dispatch_uid()
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except AttributeError:
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raise NotImplementedError('Your class %s must have a get_dispatch_uid classmethod.' % class_name)
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if dispatch_uid is not None:
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try:
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signal = new_class.signal
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except AttributeError:
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raise NotImplementedError('Your class %s must have a signal argument, which must be a Django Signal instance.' % class_name)
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else:
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signal.connect(new_class, dispatch_uid=dispatch_uid)
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if not hasattr(new_class, 'check_permission'):
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setattr(new_class, 'check_permission', check_permission)
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return new_class
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@classmethod
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def get_all_objects(cls, request):
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"""
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Collects all objects of the class created by the SignalConnectMetaClass
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from all apps via signal. If they have a default weight, they are sorted.
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Does not return objects where check_permission returns False.
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Expects a request object.
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This classmethod is added as get_all classmethod to every class using the
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SignalConnectMetaClass.
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"""
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all_objects = [obj for __, obj in cls.signal.send(sender=cls, request=request) if obj.check_permission()]
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if hasattr(cls, 'get_default_weight'):
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all_objects.sort(key=lambda obj: obj.get_default_weight())
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return all_objects
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def check_permission(self):
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"""
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Returns True by default. Override this to filter some children on runtime.
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This method is added to every instance of classes using the
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SignalConnectMetaClass.
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"""
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return True
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