Engineering Design

This section describes the design of the Course Access Groups Open edX app. It aims to be succinct and focuses on three topics:

  • Hard-coded assumptions
  • Related extension points in Open edX
  • The internal models and their interaction

Besides a section to denote future plans for the app.

Hard-coded Assumptions

Ideally, this app would blend into Open edX seamlessly without requiring special configuration or dependencies. However, this level of seamless integration may come at the cost of both complexity and reliability of the app.

Therefore the app was designed to be somewhat simple with a couple of hard-coded assumptions about the platform that would uses it.

While these assumptions are hard-coded in the initial release, some of them will be revisited in future release to be either modified or completely removed.

  • Multi-tenancy: One of the main assumptions is that the platform uses the multi-tenancy (Django Site) features without having a main site of its own.
  • Dependency on edx-organizations: In order to implement a full-featured multi-tenancy app, the edx-organizations is the go-to app to implement this feature.
  • Access Control Backends: Which allows plugins like the CAG app to modify the behaviour of courseware.access.has_access function in Open edX platform. More info is one the Access Control Backends pull request. pull request.
  • Other app changes: In order for the app to work it requires three hard-coded changes into the platform that would eventually be upstreamed. For more information see :ref:supported_open_edx_version.

Course Access Groups Database Modules

Naturally, course_access_groups.models module has the most up-to date information and documentation about the database models.

Nevertheless, this section aims to provide a summary of the models design. As of writing this docs, there are five distinct new models in this app. However, when looking at the logical design we would find only three models like the following:

The CourseAccessGroup Model

This is the main model which specify which learners should have access to which courses.

This model has two Many to Many relationships:

  • Course: Courses that belongs to this group. To simplify the use relation with the Django REST Framewor it has been moved to its own model named GroupCourse.
  • User: Users who are member of this group. For the same reasons above it has it’s own model named Membership.

This model is the only essential model for this app to run. The others can be thought of as complementary.

The PublicCourse Model

This model is used to mark courses as public to exempt from the Course Access Group rules.

Instead of modifying CourseOverview to have an additional boolean field e.g. CourseOverview.cag_is_public, a new model has been created.

This necessary to avoid having complex database migration design and minimize the maintenance impact of this app.

The MembershipRule Model

This model is used to automatically assign learners to Course Access Groups. It utilizes the USER_ACCOUNT_ACTIVATED Django signal to match learners into groups based on their email domain name.

Future Plans

This application works on a modified fork of the Hawthorn release. This section denotes plans to support future releases the impact on the architecture of this app.

Supporting Bridgekeeper in Juniper

As of April, 2019 the Open edX team started to use Bridgekeeper for Access Control which eventually would deprecate the courseware.has_access function.

The plan to support Bridgekeeper is to remove the hooks for has_access and replace them with bridgekeeper.perms[] rules.

For more information about Bridgekeeper check the project documentation: https://bridgekeeper.readthedocs.io/.

This is probably the change with the most impact. So far there’s no concrete plan to adapt to it.

In addition to this documentation please consider taking a look at the Access Control Backends thread on Open edX Discuss. It touches on a couple of related topics regarding Bridgekeeper and some recommendation from the edX engineers.

Single-site Setups

The majority of the Open edX Platform installations are single-site setups in which Site Configurations isn’t used. This application doesn’t support such installations at the moment. Several modifications needs to be done to support this installation. Here are few that we are already aware of:

  • A new flag to select the mode of the app e.g. FEATURES['COURSE_ACCESS_GROUPS_IS_MULTISITE'].
  • CourseAccessGroup.organization to be optional: This can be done in two methods: A) Make the field null=True or make a new SiteWideCourseAccessGroup to avoid having null values. My (Omar) preference is having a second module.
  • Some queries checks either of UserOrganizationMapping and OrganizationCourse. Those queries won’t work on the single-site setups so it needs to be refactored.

Open Question: Do we want to support both site-wide and organization-specific mode at the same time? The initial assumption that it would be very costly and would complicate the app. Anyway, that’s still an open question.