Issue 1694: node_referenced_by_field condition plugin

[seth-shaw-unlv]

GitHub Issue: Islandora/documentation#1694

What does this Pull Request do?

Adds a context condition plugin to detect if is a node is referenced by the configured field. It can be used, for example, to determine if a node is referenced by field_member_of, useful for complex objects. It isn't currently used by any islandora contexts in islandora_defaults, but is being made available as a potentially useful condition.

Sidenote: this plugin could be fairly easily modified to also include a count threshold, e.g. is referenced by at least n nodes... but that is a PR for another day.

What's new?

• Added the aforementioned context plugin.

How should this be tested?

• Apply the PR
• clear the cache
• either modify the collection context to use this new condition with field_member_of, instead of the term-based one, or create a new complex object condition that does something (such as changing the theme).
• Create a node referenced another node (e.g. "Node A" referenced by "Node B").
• Visit the referenced node (e.g. "Node A" from before) and observe the configured condition take effect.

Addendum:

• Visit the block placement UI to ensure it doesn't show up there.

Interested parties

@Islandora/8-x-committers, esp @rosiel.

[rosiel]

Seth this is amazing! One thing to mention is that "Node referenced by field" took a while to parse (for someone who didn't know what it was talking about before hand). I know this is a bit more verbose, but maybe

'Node is the target of an entity reference field'
or
'Node is referenced by other entities'
?

[seth-shaw-unlv]

I suppose we could use "Node is referenced by other nodes" since the form only supplies entity reference fields associated with nodes in the dropdown.

[seth-shaw-unlv]

Although that isn't strictly accurate, because a node referencing itself would still return true.

[manez]

I like 'Node is referenced by other entities,' from a non-dev perspective. If "Node is referenced by other nodes" is accurate, then that's simpler still, at least for my comfort level with Drupal.

[seth-shaw-unlv]

I made some changes, @rosiel and @manez. Hopefully that is more clear.

[manez]

👍 from me on the wording.

[mjordan]

I'll smoketest this.

[dannylamb]

Just realizing this now. We'll need to unset this here: https://github.com/Islandora/islandora/blob/8.x-1.x/islandora.module#L410

[mjordan]

Works as advertised, doesn't show up in block placement widget, watchdog is clean. Ready to merge.

[mjordan]

Reviewed and smoke tested.