Add a 'Pass Through URI' Data Converter to JSON-LD: Issue-1581

[seth-shaw-unlv]

GitHub Issue: Islandora/documentation#1581

What does this Pull Request do?

Adds a converter for RDF maps to take the targets of an entity reference field and replace their URI with the value of a Link or Authority Link fields (e.g. the Islandora taxonomy vocabularies or Genre taxonomy vocabulary).

What's new?

• Changes EntityReferenceItemNormalizer to support the DataConverter to populate '@id' (if '@id' is set as the datatype) OR the '@value'. It also only adds the target entity as another graph if not using the converter.
• Adds EntityReferenceConverter that will replace the target entity with the value of a field as passed with a 'link_field' argument in the RDF mapping.
• Updates the tests so they run without deprecation notices.
• Does this change add any new dependencies? No.
• Does this change require any other modifications to be made to the repository
  (i.e. Regeneration activity, etc.)? No.
• Could this change impact execution of existing code? No.

How should this be tested?

• Take a site with a node that references some taxonomies where the terms have a link (or authority link) field with a value. E.g. a subject term with an id.loc.gov URI.
• View the JSON-LD of that node. You will see the field mapped as usual to use the predicate in the RDF mapping where the value is the referenced taxonomy term URI.
• Apply the PR
• Update the RDF mapping so that field uses the new converter. E.g.

  field_subject:
    properties:
      - 'dcterms:subject'
    datatype_callback:
      callable: 'Drupal\jsonld\EntityReferenceConverter::linkFieldPassthrough'
      arguments:
        link_field: 'field_authority_link'

• Clear cache
• View the node's JSON-LD again. Instead of seeing the taxonomy term URI you will see the value of the term's link field (e.g. the id.loc.gov URI for a subject).

Interested parties

@Islandora/8-x-committers

[seth-shaw-unlv]

I just realized that using the converter with a term that doesn't have the value doesn't fall back to the original serialization as I thought it would. But here is my WIP if folks want to look at it now.

[seth-shaw-unlv]

Came back for a few minutes this evening to finish the PR off. It now supports the case where a Converter passes along a fieldable entity (either a new target or the original one, it doesn't care).

I believe you were interested in this one, @elizoller. Let me know what you think.

[elizoller]

This worked well for me. Tested on the resource type and the subject fields in the repository item content type in an islandora-playbook instance.
I also gave it a whirl in the context of our ASU install because I have quite a few other customizations to the RDF mapping - it worked well there also.

[whikloj]

This works for my test, it does require some RDF changes to enable it. Seeing as how it allows non-matching targets to fall through it might be nice if it was just used by default. We'd need to add a configuration field in the UI to set the link_field argument.

Just a thought, I'm good with this as is and that as a possible later piece of work.

[whikloj]

I know there is no 24 hour 🕐 in Islandora 8, but its Friday. So I'll give the other @Islandora/8-x-committers the day to have a look at this, if there is no issues/concerns raised I'll merge it.

[seth-shaw-unlv]

Can haz squash and merge, @elizoller or @whikloj?