pluginfield.py

from django.db import models
from django.conf import settings
import pkgutil
import os
from importlib import import_module
from functools import partialmethod


class PluginField(models.CharField):
    """
    1) Create 'plugins' path in your application directory
    2) Declare Plugin class with 'name' property
    3) in models.py:
            class YourModel(models.Model):
                plugin = PluginField()
            
    4) Get Plugin instance:
            obj = YourModel.objects.get(id=1)
            instance = obj.get_plugin_instance()
    https://gist.github.com/rluts/242196b2289b7bb1fac6ca2a63d09841
    """
    description = 'Plugin field'

    def __init__(self, plugins_path='plugins', *args, **kwargs):
        self.plugins_path = plugins_path
        kwargs['max_length'] = 255
        super(PluginField, self).__init__(*args, **kwargs)

    def deconstruct(self):
        name, path, args, kwargs = super().deconstruct()
        del kwargs["max_length"]
        return name, path, args, kwargs

    def _plugin_choices(self):
        module_path = os.path.join(settings.BASE_DIR, self.app_label, self.plugins_path)
        for pack in pkgutil.walk_packages([module_path]):
            loader = import_module('.'.join([self.app_label, self.plugins_path, pack.name]))
            yield (pack.name, loader.Plugin.name)

    def _check_choices(self):
        if hasattr(self, 'model'):
            self.app_label = self.model._meta.app_label
            self.choices = list(self._plugin_choices())
            self.help_text = 'You can add new plugin to %s path' % os.path.join(self.app_label, self.plugins_path)
        return super(PluginField, self)._check_choices()

    def _get_loader(self, instance, *args):
        loader = import_module('.'.join(
            [self.model._meta.app_label, self.plugins_path, getattr(instance, self.attname)])
        )
        return loader.Plugin()

    def contribute_to_class(self, cls, name, **kwargs):
        super().contribute_to_class(cls, name, **kwargs)
        instance = getattr(cls, self.attname)
        setattr(cls, 'get_%s_instance' % self.name, partialmethod(self._get_loader, instance))