Handle redirected Wikidata items

docs/index.rst

@@ -27,3 +27,4 @@ we will endevour to fix up the manual to make it clearer about that topic.
 
    install
    config
+   tags

docs/tags.rst

@@ -0,0 +1,36 @@
+.. _tags:
+
+Tags
+====
+
+Tags are the primary way of grouping Posts together by topic; each Post can have any number of Tags.
+Each Tag has its own page (with a URL of the form ``/Txx``, where ``xx`` is the Tag's ID)
+and on that page it has
+a title (which must be unique),
+and optional description (which uses the same syntax as Post bodies).
+
+Wikidata
+--------
+
+Tags can also be linked to Wikidata_ items.
+This is the way to show that a Tag's topic is *the same as* the concept represented by the Wikidata item.
+For example, a Tag with a title of "Douglas Adams" would have the Wikidata item ID of "Q42_".
+Only one Tag can be linked to each Wikidata item.
+Adding a Wikidata link to a Tag adds a metadata table to the Tag's page,
+showing all the relevant metadata from the Wikidata item.
+If a row in the metadata table refers to another Tag that is also linked to Wikidata,
+then the value displayed will be a link to that Tag.
+
+Wikidata items can be merged_ (when multiple are accidentally created for the same concept),
+but this doesn't affect the linkage from Twyne.
+The only change will be that the new ID for the item will be displayed in the metadata table;
+no data in the database is changed, because the old ID will remain on Wikidata as a permanent alias for the new one.
+
+The metadata from Wikidata is fetched up every time someone views a Tag's page, and is cached for two weeks.
+The cache can be cleared (forcing it to fetch the latest data) by running the following CLI command::
+
+    ./bin/console cache:pool:clear cache.app
+
+.. _Wikidata: https://www.wikidata.org/
+.. _Q42: https://www.wikidata.org/wiki/Q42
+.. _merged: https://www.wikidata.org/wiki/Help:Merge

src/Repository/WikidataRepository.php

@@ -70,20 +70,23 @@ public function search(string $q)
     }
 
     /**
-     * @param $id
-     * @return array With keys 'label', 'description', 'properties' and maybe 'authorities'.
+     * @param string $id
+     * @return array With keys 'id', 'label', 'description', 'properties' and maybe 'authorities'.
+     * The ID will differ from $id if the entity has been redirected.
      */
-    public function getData($id): array
+    public function getData(string $id): array
     {
         $entity = $this->getEntities([$id])[$id];
         if (!isset($entity['labels'])) {
             return [
+                'id' => '',
                 'label' => '',
                 'description' => '',
                 'properties' => [],
             ];
         }
         $out = [
+            'id' => $entity['id'],
             'label' => $entity['labels']['en']['value'] ?? '(No label)',
             'description' => $entity['descriptions']['en']['value'] ?? '(No description)',
             'properties' => [],
@@ -177,11 +180,13 @@ public function getEntities(array $ids)
                     throw new Exception('Entities not found in response.');
                 }
                 foreach ($responseData['entities'] as $entity) {
+                    // Handle redirected IDs, storing them under the original ID rather than the actual one.
+                    $entityId = $entity['redirects']['from'] ?? $entity['id'];
                     // Cache each entity for two weeks.
-                    $cacheItems[$entity['id']]->set($entity);
-                    $cacheItems[$entity['id']]->expiresAfter(new DateInterval('P14D'));
-                    $this->cache->save($cacheItems[$entity['id']]);
-                    $out[$entity['id']] = $entity;
+                    $cacheItems[$entityId]->set($entity);
+                    $cacheItems[$entityId]->expiresAfter(new DateInterval('P14D'));
+                    $this->cache->save($cacheItems[$entityId]);
+                    $out[$entityId] = $entity;
                 }
             }
             $this->cache->commit();

templates/tag/view.html.twig

@@ -19,7 +19,7 @@
                 <caption>
                     <img src="{{ asset('build/images/wikidata-logo.png') }}" alt="Wikidata logo." />
                     Wikidata item
-                    <a href="https://www.wikidata.org/wiki/{{ tag.wikidata }}">{{ tag.wikidata }}</a>:
+                    <a href="https://www.wikidata.org/wiki/{{ entity.id }}">{{ entity.id }}</a>:
                     <strong>{{ entity.label }}</strong>
                     {% if entity.description %}
                         &mdash; <dfn>{{ entity.description }}</dfn>

tests/Repository/WikidataRepositoryTest.php

@@ -0,0 +1,19 @@
+<?php
+
+namespace App\Test\Repository;
+
+use App\Repository\WikidataRepository;
+use App\Tests\Repository\RepositoryTestBase;
+
+class WikidataRepositoryTest extends RepositoryTestBase
+{
+
+    public function testGetData()
+    {
+        /** @var WikidataRepository $wikidataRepo */
+        $wikidataRepo = self::$container->get(WikidataRepository::class);
+        // Redirected item.
+        $data = $wikidataRepo->getData('Q73007800');
+        $this->assertSame('Q5501480', $data['id']);
+    }
+}