identifier of referenced schema properties in search API fields

[stefan-korn]

It might be helpful to have the identifier (node UUID) of referenced schema properties in the search API fields as well.

For example: for a publisher referenced in a dataset, all the properties under the data tree in the schema are available as search API fields. But the identifier property is missing, since it is missing under the data properties.

I was thinking about integrating the identifier like this:

diff --git a/modules/metastore/modules/metastore_search/src/ComplexData/Dataset.php b/modules/metastore/modules/metastore_search/src/ComplexData/Dataset.php
index 252ce210c..88a9cdbae 100644
--- a/modules/metastore/modules/metastore_search/src/ComplexData/Dataset.php
+++ b/modules/metastore/modules/metastore_search/src/ComplexData/Dataset.php
@@ -37,7 +37,17 @@ class Dataset extends ComplexDataFacade {
       $defs = self::getPropertyDefinition($type, $object, $property);
       $definitions = array_merge($definitions, $defs);
     }
-
+    foreach ($properties as $property) {
+      try {
+        $schemaRetriever->retrieve($property);
+        $type = $object->properties->{$property}->type ?? "string";
+        $defs = self::getPropertyDefinition($type, $object, '%Ref:'.$property.'__identifier');
+        $defs['%Ref:'.$property.'__identifier']->setLabel('Identifier');
+        $definitions = array_merge($definitions, $defs);
+      } catch (\Exception $exception) {
+        // no reference, skip
+      }
+    }
     return $definitions;
   }

This could surely be improved in some ways (label, retrieving of subschema etc.). But in general this should add the identifier to the search API fields for referenced properties.

[stefan-korn]

Played a bit more with this and noticed while this is basically working together with the DKAN extra fields module, it has issues with indexing the property in Search API, because of the property name using a colon and a percent symbol. This would need to be mapped in something else for the definition and later when getting the value of the property it needs to be mapped back. I tested replacing %Ref with _Ref_ and this seems to be working, though that would need some more adjustments than the patch above. If there is interest in this, I can explain further, provide another patch.