perf(core): Improve speed & memory usage when running collection filters

Relates to #1893

packages/core/src/service/services/collection.service.ts

@@ -560,13 +560,13 @@ export class CollectionService implements OnModuleInit {
     }
 
     private chunkArray = <T>(array: T[], chunkSize: number): T[][] => {
-        const results = []
+        const results = [];
         for (let i = 0; i < array.length; i += chunkSize) {
-          results.push(array.slice(i, i + chunkSize))
+            results.push(array.slice(i, i + chunkSize));
         }
-      
-        return results
-      }
+
+        return results;
+    };
 
     /**
      * Applies the CollectionFilters
@@ -587,44 +587,42 @@ export class CollectionService implements OnModuleInit {
             ),
         );
         const preIds = await this.getCollectionProductVariantIds(collection);
-        collection.productVariants = await this.getFilteredProductVariants([
+        const filteredVariantIds = await this.getFilteredProductVariantIds([
             ...ancestorFilters,
             ...(collection.filters || []),
         ]);
-        const postIds = collection.productVariants.map(v => v.id);
+        const postIds = filteredVariantIds.map(v => v.id);
         const preIdsSet = new Set(preIds);
         const postIdsSet = new Set(postIds);
 
-        const toDeleteIds = preIds.filter((id) => !postIdsSet.has(id))
-        const toAddIds = postIds.filter((id) => !preIdsSet.has(id))
+        const toDeleteIds = preIds.filter(id => !postIdsSet.has(id));
+        const toAddIds = postIds.filter(id => !preIdsSet.has(id));
 
         try {
             // First we remove variants that are no longer in the collection
-            const chunkedDeleteIds = this.chunkArray(toDeleteIds, 500)
+            const chunkedDeleteIds = this.chunkArray(toDeleteIds, 500);
 
             for (const chunkedDeleteId of chunkedDeleteIds) {
                 await this.connection.rawConnection
-                  .createQueryBuilder()
-                  .relation(Collection, 'productVariants')
-                  .of(collection)
-                  .remove(chunkedDeleteId)
-              }
+                    .createQueryBuilder()
+                    .relation(Collection, 'productVariants')
+                    .of(collection)
+                    .remove(chunkedDeleteId);
+            }
 
             // Then we add variants have been added
-            const chunkedAddIds = this.chunkArray(toAddIds, 500)
+            const chunkedAddIds = this.chunkArray(toAddIds, 500);
 
             for (const chunkedAddId of chunkedAddIds) {
-            await this.connection.rawConnection
-                .createQueryBuilder()
-                .relation(Collection, 'productVariants')
-                .of(collection)
-                .add(chunkedAddId)
+                await this.connection.rawConnection
+                    .createQueryBuilder()
+                    .relation(Collection, 'productVariants')
+                    .of(collection)
+                    .add(chunkedAddId);
             }
-
         } catch (e) {
             Logger.error(e);
         }
-        
 
         if (applyToChangedVariantsOnly) {
             return [...preIds.filter(id => !postIdsSet.has(id)), ...postIds.filter(id => !preIdsSet.has(id))];
@@ -636,7 +634,7 @@ export class CollectionService implements OnModuleInit {
     /**
      * Applies the CollectionFilters and returns an array of ProductVariant entities which match.
      */
-    private async getFilteredProductVariants(filters: ConfigurableOperation[]): Promise<ProductVariant[]> {
+    private async getFilteredProductVariantIds(filters: ConfigurableOperation[]): Promise<Array<{ id: ID }>> {
         if (filters.length === 0) {
             return [];
         }
@@ -654,7 +652,9 @@ export class CollectionService implements OnModuleInit {
             }
         }
 
-        return qb.getMany();
+        // This is the most performant (time & memory) way to get
+        // just the variant IDs, which is all we need.
+        return qb.select('productVariant.id', 'id').getRawMany();
     }
 
     /**