fix: handle duplicates when applying CompontentType constraint

[bradenmacdonald]

Implements #548

This improves content migration 0004 so that installations with invalid duplicates (which exist, see example) will have their data cleaned up automatically.

How to test

You can run this script to test using SQLite with the django test settings:

DJANGO_SETTINGS_MODULE=test_settings python <<'EOF'
import django
django.setup()

from django.core.management import call_command
from django.db.migrations.executor import MigrationExecutor
from django.db import connection
from django.utils import timezone
import uuid

call_command('migrate', 'openedx_content', '0003', verbosity=0)
executor = MigrationExecutor(connection)
state = executor.loader.project_state(("openedx_content", "0003_rename_content_to_media"))
ComponentType = state.apps.get_model('openedx_content', 'ComponentType')
Component = state.apps.get_model('openedx_content', 'Component')
LearningPackage = state.apps.get_model('openedx_content', 'LearningPackage')
PublishableEntity = state.apps.get_model('openedx_content', 'PublishableEntity')

now = timezone.now()
lp = LearningPackage.objects.create(key='lp1', title='Test', created=now, updated=now, uuid=uuid.uuid4())

# Create duplicate ComponentTypes (allowed before migration 0004)
ct1 = ComponentType.objects.create(namespace='xblock.v1', name='problem')
ct2 = ComponentType.objects.create(namespace='xblock.v1', name='problem')
ct3 = ComponentType.objects.create(namespace='xblock.v1', name='problem')
ct_other = ComponentType.objects.create(namespace='xblock.v1', name='video')
ct_html_a = ComponentType.objects.create(namespace='xblock.v1', name='html')
ct_html_b = ComponentType.objects.create(namespace='xblock.v1', name='html')
print(f"Pre-migration ComponentTypes: {sorted(ComponentType.objects.values_list('id', 'namespace', 'name'))}")

# Create some components pointing to duplicates
pe1 = PublishableEntity.objects.create(learning_package=lp, key='c1', uuid=uuid.uuid4(), created=now)
pe2 = PublishableEntity.objects.create(learning_package=lp, key='c2', uuid=uuid.uuid4(), created=now)
pe3 = PublishableEntity.objects.create(learning_package=lp, key='c3', uuid=uuid.uuid4(), created=now)
c1 = Component.objects.create(publishable_entity=pe1, learning_package=lp, component_type=ct2, local_key='one')
c2 = Component.objects.create(publishable_entity=pe2, learning_package=lp, component_type=ct3, local_key='two')
c3 = Component.objects.create(publishable_entity=pe3, learning_package=lp, component_type=ct_other, local_key='three')

call_command('migrate', 'openedx_content', '0004', verbosity=0)

state = executor.loader.project_state(("openedx_content", "0004_componenttype_constraint"))
ComponentType = state.apps.get_model('openedx_content', 'ComponentType')
Component = state.apps.get_model('openedx_content', 'Component')

print(f"Post CTs: {sorted(ComponentType.objects.values_list('id', 'namespace', 'name'))}")
print(f"  c1.ct = {Component.objects.get(pk=c1.pk).component_type_id} (expect {ct1.id})")
print(f"  c2.ct = {Component.objects.get(pk=c2.pk).component_type_id} (expect {ct1.id})")
print(f"  c3.ct = {Component.objects.get(pk=c3.pk).component_type_id} (expect {ct_other.id})")

# Verify constraint is in place
try:
    ComponentType.objects.create(namespace='xblock.v1', name='problem')
    print("❌ should have rejected duplicate")
except Exception as e:
    print(f"✅ constraint rejected duplicate ({type(e).__name__})")
EOF

[openedx-webhooks]

Thanks for the pull request, @bradenmacdonald!

This repository is currently maintained by @axim-engineering.

Once you've gone through the following steps feel free to tag them in a comment and let them know that your changes are ready for engineering review.

🔘 Get product approval

If you haven't already, check this list to see if your contribution needs to go through the product review process.

• If it does, you'll need to submit a product proposal for your contribution, and have it reviewed by the Product Working Group.
  • This process (including the steps you'll need to take) is documented here.
• If it doesn't, simply proceed with the next step.

🔘 Provide context

To help your reviewers and other members of the community understand the purpose and larger context of your changes, feel free to add as much of the following information to the PR description as you can:

• Dependencies

  This PR must be merged before / after / at the same time as ...

• Blockers

  This PR is waiting for OEP-1234 to be accepted.

• Timeline information

  This PR must be merged by XX date because ...

• Partner information

  This is for a course on edx.org.

• Supporting documentation
• Relevant Open edX discussion forum threads

🔘 Get a green build

If one or more checks are failing, continue working on your changes until this is no longer the case and your build turns green.

Details

---

Where can I find more information?

If you'd like to get more details on all aspects of the review process for open source pull requests (OSPRs), check out the following resources:

• Overview of Review Process for Community Contributions
• Pull Request Status Guide
• Making changes to your pull request

When can I expect my changes to be merged?

Our goal is to get community contributions seen and reviewed as efficiently as possible.

However, the amount of time that it takes to review and merge a PR can vary significantly based on factors such as:

• The size and impact of the changes that it introduces
• The need for product review
• Maintenance status of the parent repository

💡 As a result it may take up to several weeks or months to complete a review and merge your PR.

[ormsbee]

I think this is entirely reasonable, but I also don't think you can actually create new Components in practice if there are duplicates of the ComponentType because it should fail to fetch a unique result. But anyway, this can't hurt.

[bradenmacdonald]

I also don't think you can actually create new Components in practice if there are duplicates of the ComponentType because it should fail to fetch a unique result

Sorry, I'm not following. Isn't that exactly the bug we're trying to solve, and exactly the problem that was reported on the forum?

[ormsbee]

Sorry, I was thinking that it was definitely possible to create duplicate ComponentTypes. But when you try to create a Component, I thought it would error out when trying to fetch the type because there are duplicates. But I was forgetting that it's a get_or_create kind of deal, so it would be good for inserting that one Component during the race condition, even if future attempts to create Components of that type would always error out because there are multiple ComponentTypes that match.

[ormsbee]

So in any case, yeah, this code all makes sense. Thank you. 😄