GQL: Request labels in batch

This reduces the number of DB queries to fetch labels. It combines the
labels to fetch of the main item with the ones to fetch of statement
properties. In theory, this could result in over-fetching if item labels
are requested in different languages than the statement property labels,
but in reality this is unlikely and probably not worth optimizing.

Bug: T400146
Change-Id: Ie92b5bfaad562649c284b6de41d4d533c4903f6a

Author: jakobw

repo/includes/GraphQLPrototype/LabelsResolver.php

@@ -2,6 +2,7 @@
 
 namespace Wikibase\Repo\GraphQLPrototype;
 
+use GraphQL\Deferred;
 use GraphQL\Type\Definition\ResolveInfo;
 use Wikibase\DataAccess\PrefetchingTermLookup;
 use Wikibase\DataModel\Entity\BasicEntityIdParser;
@@ -12,19 +13,31 @@
  */
 class LabelsResolver {
 
+	private array $entityIdsBatch = [];
+	private array $languageCodesBatch = [];
+	private bool $hasPrefetched = false;
+
 	public function __construct( private PrefetchingTermLookup $termLookup ) {
 	}
 
-	public function fetchLabels( array $rootValue, ResolveInfo $info ): array {
+	public function fetchLabels( array $rootValue, ResolveInfo $info ): Deferred {
 		$entityId = ( new BasicEntityIdParser() )->parse( $rootValue['id'] );
 		$languageCodes = array_keys( $info->getFieldSelection() );
 
-		$this->termLookup->prefetchTerms(
-			[ $entityId ],
-			[ TermTypes::TYPE_LABEL ],
-			$languageCodes
-		);
+		$this->entityIdsBatch[] = $entityId;
+		$this->languageCodesBatch = array_merge( $this->languageCodesBatch, $languageCodes );
+
+		return new Deferred( function() use( $entityId, $languageCodes ) {
+			if ( !$this->hasPrefetched ) {
+				$this->termLookup->prefetchTerms(
+					array_unique( $this->entityIdsBatch ),
+					[ TermTypes::TYPE_LABEL ],
+					array_unique( $this->languageCodesBatch )
+				);
+				$this->hasPrefetched = true;
+			}
 
-		return $this->termLookup->getLabels( $entityId, $languageCodes );
+			return $this->termLookup->getLabels( $entityId, $languageCodes );
+		} );
 	}
 }