Caused by changes to page repo in reference work,
This adds back in the slug generate although at a more central place.
Adds a test case to cover the problematic scenario.
Added additional exceptions to prevent such cases in the future, so
that they are caught in dev ideally.
Added test case specifically for reported favourite scenario.
Decided it's relevant to entity updated_at since tags are now indexed
alongside content.
- Also fixed tags not applied on shelf.
- Also enforced proper page API update validation.
- Adds tests to cover.
For #3319Fixes#3370
* Started mass-refactoring of the current entity repos
* Rewrote book tree logic
- Now does two simple queries instead of one really complex one.
- Extracted logic into its own class.
- Remove model-level akward union field listing.
- Logic now more readable than being large separate query and
compilation functions.
* Extracted and split book sort logic
* Finished up Book controller/repo organisation
* Refactored bookshelves controllers and repo parts
* Fixed issues found via phpunit
* Refactored Chapter controller
* Updated Chapter export controller
* Started Page controller/repo refactor
* Refactored another chunk of PageController
* Completed initial pagecontroller refactor pass
* Fixed tests and continued reduction of old repos
* Removed old page remove and further reduced entity repo
* Removed old entity repo, split out page controller
* Ran phpcbf and split out some page content methods
* Tidied up some EntityProvider elements
* Fixed issued caused by viewservice change
