What exactly is the CD2 migration_id and how is it meant to be used?

[jhveem]

Problem

I've noticed there are entries in most course content items for a migration_id. My assumption was this was a way to join with the content_migrations table, but the id in that table doesn't match the format of the migration_id. 

What I'm Trying to Do

I'd first off just like to understand what the migration_id and content_migrations.id are meant to do. As an example of a specific project, I'd like to look up a given assignment/quiz/page/etc. and track that content item back to the course where it was originally created through its content_migrations. However, since the migration_id and content_migrations.id don't appear to be related, I'm stumped.

TLDR;

Is there a relationship between a content item's (assignment/quiz/page/etc.) migration_id and content_migrations.id?

If not, what are they meant to be used for?

Is there a way to see which course a content item came from (whether through migration_ids or something else?)

I assume I'm missing something obvious, but if someone could point me in the right direction, that would be great.

Thanks!

[stimme]

Hi @jhveem ! The migration_id appears to be a key for master_courses_master_migrations.id. It should appear for content created by Blueprint syncs according to the CD2 documentation.

[jhveem]

Thanks, I looked through the documentation, and I don't think that's quite right. The migration_id field descriptions I checked don't mention blueprints, and I checked several quizzes in our cd2 that I know for sure didn't come from blueprint migrations and they have a migration id (~90% of all our content has a migration id and we only have about a dozen blueprints). But I think you're in the right direction.

My working theory, assuming I understand the docs, is that this is a unique identifier used for any content copied in any way (blueprint syncs, course copy, content import, etc.) that Canvas uses to determine if a migration should replace existing content or create something new.

[stimme]

This sounds right. The note for assignments.migration_id indicates as much. The note for wiki_pages.migration_id says it is related to blueprints. But I think that must be wrong, because the vast majority of our pages have migration_ids, and very few of our courses are associated to blueprints.

[sgergely]

The Entity Relationship Diagram might help you in that question I beleive: https://data-access-platform-api.s3.amazonaws.com/erd/index.html

[jhveem]

Thanks, I checked a few content types, but according to that, the Migration Id it isn't related to anything.

[sgergely]

Thanks for bringing this topic up and keeping it alive. I'm always interested in such questions because this is a great opportunity to improve our documentation.

I have asked around what are these migration_ids from Canvas developers and got the following info:

The migration_id is a hash of the original object’s asset string (type+global id) that was exported in a content migration. It serves as the identifier in the common cartridge XML and it also allows Canvas to recognize when the same object is reimported so it can update instead of duplicate it. Course copy, blueprint, content export/import all use the migration_id. Customers could conceivably use the migration_id in DAP to identify objects such as assignments that were all copied from a common source.

Hope this helps, let me know if you have follow-up questions.