Merge pull request #7726 from szubster/lunr-filter-single-item-array

Handle single-item array filter in Lunr search engine

.changeset/search-spicy-foxes-joke.md

@@ -0,0 +1,5 @@
+---
+'@backstage/plugin-search-backend-node': patch
+---
+
+Handle special case when filter array has single value optimizing Lunr search behaviour.

plugins/search-backend-node/src/engines/LunrSearchEngine.test.ts

@@ -192,6 +192,37 @@ describe('LunrSearchEngine', () => {
       });
     });
 
+    it('should handle single-item array filter as scalar value', async () => {
+      const inspectableSearchEngine = new LunrSearchEngineForTranslatorTests({
+        logger: getVoidLogger(),
+      });
+      const translatorUnderTest = inspectableSearchEngine.getTranslator();
+
+      const actualTranslatedQuery = translatorUnderTest({
+        term: 'testTerm',
+        filters: { kind: ['testKind'] },
+      }) as ConcreteLunrQuery;
+
+      expect(actualTranslatedQuery).toMatchObject({
+        documentTypes: undefined,
+        lunrQueryBuilder: expect.any(Function),
+      });
+
+      const query: jest.Mocked<lunr.Query> = {
+        allFields: ['kind'],
+        clauses: [],
+        term: jest.fn(),
+        clause: jest.fn(),
+      };
+
+      actualTranslatedQuery.lunrQueryBuilder.bind(query)(query);
+
+      expect(query.term).toBeCalledWith(lunr.tokenizer('testKind'), {
+        fields: ['kind'],
+        presence: lunr.Query.presence.REQUIRED,
+      });
+    });
+
     it('should return translated query with multiple filters', async () => {
       const inspectableSearchEngine = new LunrSearchEngineForTranslatorTests({
         logger: getVoidLogger(),

plugins/search-backend-node/src/engines/LunrSearchEngine.ts

@@ -80,11 +80,17 @@ export class LunrSearchEngine implements SearchEngine {
         });
 
         if (filters) {
-          Object.entries(filters).forEach(([field, value]) => {
+          Object.entries(filters).forEach(([field, fieldValue]) => {
             if (!q.allFields.includes(field)) {
               // Throw for unknown field, as this will be a non match
               throw new Error(`unrecognised field ${field}`);
             }
+            // Arrays are poorly supported, but we can make it better for single-item arrays,
+            // which should be a common case
+            const value =
+              Array.isArray(fieldValue) && fieldValue.length === 1
+                ? fieldValue[0]
+                : fieldValue;
 
             // Require that the given field has the given value
             if (['string', 'number', 'boolean'].includes(typeof value)) {