Tuesday, November 1, 2016

Re: Updating mixin subclassed instances

You could use a metaclass to keep track of all the classes that inherit from a given one, in a pure Python way it would be something like this

class PluginMeta(type):      # we use __init__ rather than __new__ here because we want      # to modify attributes of the class *after* they have been      # created      def __init__(cls, name, bases, dct):          if not hasattr(cls, 'registry'):              # this is the base class.  Create an empty registry              cls.registry = {}          else:              # this is a derived class.  Add cls to the registry              interface_id = name.lower()              cls.registry[interface_id] = cls          super(PluginMeta, cls).__init__(name, bases, dct)    class Plugin(object):      __metaclass__ = PluginMeta  


So, all the classes that inherit from Plugin are stored in Plugin.registry. Not sure if it works for mixins though.

On Mon, Oct 31, 2016 at 4:03 PM, Radek Svarz <radek.svarz@gmail.com> wrote:
Hi,

I am using my custom permission mixin on several of my apps's models (not all).

For the case when I need to merge from the "old - context" permission to the "new - context" permission I want to have function which changes the corresponding permission reference attribute in all models, which subclassed this mixin.

How do I know which models subclassed this permission mixin and that they have the inherited permission reference attribute?

In fact I want to have such function in my mixin:

@classmethod
def merge_to(cls, from_perm_context, to_perm_context):

    perm_context_models = []  # How to get this?

    try:
        with transaction.atomic():
            for model in perm_context_models:
                model.objects.filter(
                    perm_context=from_perm_context,
                ).update(perm_context=to_perm_context)
    except IntegrityError as e:  # or DatabaseError
        raise e



Thanks, 

Radek

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