☂️ Merge Course and CoursePage

[elbotho]

intro

similar to moving solutions into the editor state of the parent exercise we want to move the course pages into the editor state of the parent course.

why?

• simplify backend and entities
• simplify reviewing
• hopefully less bugs

impact

Last entity with entity children. Finishing this will unlock a lot of simplifications across our codebase

potential problems

• we use the coursePage urls directly quite a bit
• we have to handle SEO
• editing experience might be annoying for long courses (solved here)

plan/unclear

• find a way to link to page directly after migration (like GroupedEx)
• Note: not supporting injections is probably ok (source) (but could be supported like we do with GroupedEx)
• change existing links and relatedContent (db-migration)
• improve edit UI so it's not overwhelming for long courses? (solved here)

migrate

• update course editor state in frontend
• build migration to move all course pages into the parent courses editor state
• adapt frontend
  • show pages from state
  • change how urls are created
  • change author menus
  • remove CoursePage entity code
  • …
• add redirect in cf-worker to 301 previously existing coursePage links and remove existing course redirects
• test changes

cleanup

• remove code from api
• remove code from db layer
• delete coursePages from db (migration)

links

We need to think about way to directly
we should def. update existing links

[Entkenntnis]

SEO would be the biggest task: About 9% of our total traffic are course pages and most of the time it's not the first page, but some other page like https://de.serlo.org/mathe/20322/addition-und-subtraktion-ungleichnamige-brüche. Course pages are de-facto "mini articles".

The most painless path here would be to keep all urls backward compatible - the very least to redirect them so that google can find them.

[elbotho]

closing in favour of serlo/db-migrations#338