Add a facility for building stacked configuration models that control the same configuration on a Global, Site, Org and Course level

cms/envs/common.py

@@ -997,6 +997,7 @@ INSTALLED_APPS = [
 
     # Database-backed configuration
     'config_models',
+    'openedx.core.djangoapps.config_model_utils',
     'waffle',
 
     # Monitor the status of services

lms/envs/common.py

@@ -2035,6 +2035,7 @@ INSTALLED_APPS = [
 
     # Database-backed configuration
     'config_models',
+    'openedx.core.djangoapps.config_model_utils',
     'waffle',
 
     # Monitor the status of services

openedx/core/djangoapps/config_model_utils/apps.py

@@ -0,0 +1,11 @@
+"""
+Django AppConfig for ConfigurationModel utilities
+"""
+# -*- coding: utf-8 -*-
+from __future__ import unicode_literals
+
+from django.apps import AppConfig
+
+
+class ConfigModelUtilsConfig(AppConfig):
+    name = 'openedx.core.djangoapps.config_model_utils'

openedx/core/djangoapps/config_model_utils/models.py

@@ -0,0 +1,180 @@
+"""
+Useful ConfigurationModel subclasses
+
+StackedConfigurationModel: A ConfigurationModel that can be overridden at site, org and course levels
+"""
+
+# -*- coding: utf-8 -*-
+from __future__ import unicode_literals
+
+from collections import namedtuple
+
+from django.conf import settings
+from django.db import models
+from django.contrib.sites.models import Site
+from django.contrib.sites.requests import RequestSite
+from django.core.exceptions import ValidationError
+from django.utils.translation import ugettext_lazy as _
+import crum
+
+from config_models.models import ConfigurationModel
+from openedx.core.djangoapps.site_configuration.models import SiteConfiguration
+from openedx.core.djangoapps.content.course_overviews.models import CourseOverview
+
+
+class StackedConfigurationModel(ConfigurationModel):
+    """
+    A ConfigurationModel that stacks Global, Site, Org, and Course level
+    configuration values.
+    """
+    class Meta(object):
+        abstract = True
+
+    KEY_FIELDS = ('site', 'org', 'course')
+    STACKABLE_FIELDS = ('enabled',)
+
+    enabled = models.NullBooleanField(default=None, verbose_name=_("Enabled"))
+    site = models.ForeignKey(Site, on_delete=models.CASCADE, null=True)
+    org = models.CharField(max_length=255, db_index=True, null=True)
+    course = models.ForeignKey(
+        CourseOverview,
+        on_delete=models.DO_NOTHING,
+        null=True,
+    )
+
+    @classmethod
+    def attribute_tuple(cls):
+        """
+        Returns a namedtuple with all attributes that can be overridden on this config model.
+
+        For example, if MyStackedConfig.STACKABLE_FIELDS = ('enabled', 'enabled_as_of', 'studio_enabled'),
+        then:
+
+            # These lines are the same
+            MyStackedConfig.attribute_tuple()
+            namedtuple('MyStackedConfigValues', ('enabled', 'enabled_as_of', 'studio_enabled'))
+
+            # attribute_tuple() behavior
+            MyStackedConfigValues = MyStackedConfig.attribute_tuple()
+            MyStackedConfigValues(True, '10/1/18', False).enabled  # True
+            MyStackedConfigValues(True, '10/1/18', False).enabled_as_of  # '10/1/18'
+            MyStackedConfigValues(True, '10/1/18', False).studio_enabled  # False
+        """
+        if hasattr(cls, '_attribute_tuple'):
+            return cls._attribute_tuple
+
+        cls._attribute_tuple = namedtuple(
+            '{}Values'.format(cls.__name__),
+            cls.STACKABLE_FIELDS
+        )
+        return cls._attribute_tuple
+
+    @classmethod
+    def current(cls, site=None, org=None, course=None):  # pylint: disable=arguments-differ
+        """
+        Return the current overridden configuration at the specified level.
+
+        Only one level may be specified at a time. Specifying multiple levels
+        will result in a ValueError.
+
+        For example, considering the following set of requirements:
+
+            Global: Feature Disabled
+            edx.org (Site): Feature Enabled
+            Harvard (org): Feature Disabled
+            CS50 (course): Feature Enabled
+
+        Assuming these values had been properly configured, these calls would result
+
+            MyStackedConfig.current()  # False
+            MyStackedConfig.current(site=Site(domain='edx.org'))  # True
+            MyStackedConfig.current(site=Site(domain='whitelabel.edx.org')) # False -- value derived from global setting
+            MyStackedConfig.current(org='HarvardX')  # False
+            MyStackedConfig.current(org='MITx')  # True -- value derived from edx.org site
+            MyStackedConfig.current(course=CourseKey(org='HarvardX', course='CS50', run='2018_Q1'))  # True
+
+            cs50 = CourseKey(org='HarvardX', course='Bio101', run='2018_Q1')
+            MyStackedConfig.current(course=cs50)  # False -- value derived from HarvardX org
+
+        The following calls would result in errors due to overspecification:
+
+            MyStackedConfig.current(site=Site(domain='edx.org'), org='HarvardX')
+            MyStackedConfig.current(site=Site(domain='edx.org'), course=cs50)
+            MyStackedConfig.current(org='HarvardX', course=cs50)
+
+        Arguments:
+            site: The Site to check current values for
+            org: The org to check current values for
+            course: The course to check current values for
+
+        Returns:
+            An instance of :class:`cls.attribute_tuple()` with the overridden values
+            specified down to the level of the supplied argument (or global values if
+            no arguments are supplied).
+        """
+        # Raise an error if more than one of site/org/course are specified simultaneously.
+        if len([arg for arg in [site, org, course] if arg is not None]) > 1:
+            raise ValueError("Only one of site, org, and course can be specified")
+
+        if org is None and course is not None:
+            org = cls._org_from_course(course)
+
+        if site is None and org is not None:
+            site = cls._site_from_org(org)
+
+        stackable_fields = [cls._meta.get_field(field_name) for field_name in cls.STACKABLE_FIELDS]
+        field_defaults = {
+            field.name: field.get_default()
+            for field in stackable_fields
+        }
+
+        values = field_defaults.copy()
+
+        global_current = super(StackedConfigurationModel, cls).current(None, None, None)
+        for field in stackable_fields:
+            values[field.name] = field.value_from_object(global_current)
+
+        def _override_fields_with_level(level_config):
+            for field in stackable_fields:
+                value = field.value_from_object(level_config)
+                if value != field_defaults[field.name]:
+                    values[field.name] = value
+
+        if site is not None:
+            _override_fields_with_level(
+                super(StackedConfigurationModel, cls).current(site, None, None)
+            )
+
+        if org is not None:
+            _override_fields_with_level(
+                super(StackedConfigurationModel, cls).current(None, org, None)
+            )
+
+        if course is not None:
+            _override_fields_with_level(
+                super(StackedConfigurationModel, cls).current(None, None, course)
+            )
+
+        return cls.attribute_tuple()(**values)
+
+    @classmethod
+    def _org_from_course(cls, course_key):
+        return course_key.org
+
+    @classmethod
+    def _site_from_org(cls, org):
+        configuration = SiteConfiguration.get_configuration_for_org(org)
+        if configuration is None:
+            try:
+                return Site.objects.get(id=settings.SITE_ID)
+            except Site.DoesNotExist:
+                return RequestSite(crum.get_current_request())
+        else:
+            return configuration.site
+
+    def clean(self):
+        # fail validation if more than one of site/org/course are specified simultaneously
+        if len([arg for arg in [self.site, self.org, self.course] if arg is not None]) > 1:
+            raise ValidationError(
+                _('Configuration may not be specified at more than one level at once.')
+            )