getRelated() not working when related entity field is empty

What would be super helpful, is a failing test which reproduces this problem :)

I've confirmed this bug exists locally. I'll write some tests for this as part of #2945093: Comprehensive JSON API integration test coverage phase 3: test JSON API-specific use cases: related/relationship routes, includes and sparse field sets.

I can't believe this has existed for so long without being noticed. Great catch @harrrrrrr!

👍 — thank you, @harrrrrrr! (Also: great nickname :D)

Assigning to myself so I don't forget about this.

This again came up while working on tests in #2945093: Comprehensive JSON API integration test coverage phase 3: test JSON API-specific use cases: related/relationship routes, includes and sparse field sets

Which led me to #2940339: Port reference field support for non-empty entity reference fields not pointing to an entity from #2543726

Which clearly is related to this issue given this line of the IS: "Function getRelated() in EntityResource.php not working when related entity field is empty becasue $field_list->entity is null."

I'm not sure if one is a duplicate of the other yet, so leaving both open. This one is for "related" routes and the other is presumably focused on "individual" routes.

The good new is that test coverage does exist now, albeit indirectly :) I'll test this patch against it shortly.

👍 — they indeed seem related and potentially even duplicates!

See #2940342-39: Cacheability metadata on an entity fields' properties is lost.

I was mistaken in #11: that is a different problem: that's about a relationship being omitted from data.relationships completely when it doesn't refer to another resource.

And interestingly, the bug reported here was fixed on February 14 in #2939722: Do not provide routes for internal resource types. Perhaps unsurprisingly, the changes suggested in the patch in #4 no longer apply because that code has been removed altogether!

That makes this effectively a duplicate that has already been fixed! :)

I found this through git bisect and … deceiving git btw :D

I found that 8.x-1.7 worked as described in the IS. But HEAD didn't. Telling git bisect that HEAD was good and 1.7 was bad wouldn't work though (because that leads git to conclude that things are good in HEAD, hence no bisecting necessary). So, just flipping good and bad allowed me to use git bisect after all :)

@gabesullice kindly pointed out that I was severely mistaken, because I was testing http://d8/jsonapi/node/article/c32bef09-21f5-4b63-a51f-29d0734edc3c/relationships/field_image instead of http://d8/jsonapi/node/article/c32bef09-21f5-4b63-a51f-29d0734edc3c/field_image…

To not have this be blocked on #2945093: Comprehensive JSON API integration test coverage phase 3: test JSON API-specific use cases: related/relationship routes, includes and sparse field sets, here's test coverage added to JsonApiFunctionalTest.

The test-only patch is also the interdiff.

#2940339: Port reference field support for non-empty entity reference fields not pointing to an entity from #2543726 is for a different problem: the fact that core REST says {target_id: null}, but JSON API just says {data: []}. Removing that from the related issues.

This is now the only remaining blocker for #2945093-37: Comprehensive JSON API integration test coverage phase 3: test JSON API-specific use cases: related/relationship routes, includes and sparse field sets.

This looks good to me. Thanks everyone! Merging.

🎉