Warn about empty typed relation entity references (issue-1489)

[seth-shaw-unlv]

GitHub Issue: Islandora/documentation#1489

What does this Pull Request do?

Catches an issue where the JSON-LD will WSOD if you accidentally give it a typed relation with an empty entity reference and warns you about it.

What's new?

• Added sanity check on empty entity references in typed relations during JSON-LD alter which logs a warning.
• Does this change require any other modifications to be made to the repository
  (i.e. Regeneration activity, etc.)? You may want to re-index your repository in Fedora if you've been unwittingly loosing data to the error this fixes.

How should this be tested?

A description of what steps someone could take to:

• Somehow create a typed relation without an entity reference. (I did it by accident with a bad migration.)
• Attempt to view the resulting node's JSON-LD and see a WSOD.
• Apply the PR
• Attempt to view the node's JSON-LD again and see valid JSON-LD return
• Check your logs. There should be a warning about a missing entity reference in the typed relation field for that node.

Interested parties

@Islandora/8-x-committers

[seth-shaw-unlv]

Actually, maybe we should make the sanity check after we try to load the referenced entity, to make sure it is valid....

[seth-shaw-unlv]

@whikloj, yeah, I was wondering if that would happen. I threw that PR together on a box that didn't have phpcs installed. I'll clean this up this morning.

[jordandukart]

To refine the test case:

• Create a Person taxonomy term such that a Linked Agent can be made from an Islandora entity.
• Create an entity with that Linked Agent
• Delete the taxonomy term
• Clear the cache and attempt to retrieve the jsonld
• WSOD

[jordandukart]

This does what it says on the tin, 👍 from me.

However, noticed if you retrieve the JSONLD for a child and then delete the parent, the cache isn't invalidated and you have stale JSONLD being served. Likely needs its own issue but since I've never looked at this code before wonder if this is a known issue or if I am missing something @seth-shaw-unlv?

[seth-shaw-unlv]

@jordandukart, I agree that the JSON-LD cache invalidation is a separate issue.

I'll also note that Islandora 8 doesn't have the 24-hour wait between approval and merge. Thanks!