fix(vector):fix similar_to() error return when data is not present (#…

…9084)

When no elements are present in the HNSW tree, we return an error saying so. However, we only need to return nil result.

query/vector/vector_test.go

@@ -268,6 +268,10 @@ func querySingleVectorError(t *testing.T, vector, pred string, validateError boo
 		return []float32{}, err
 	}
 
+	if len(data.Vector) == 0 {
+		return []float32{}, nil
+	}
+
 	return data.Vector[0].VTest, nil
 }
 
@@ -569,8 +573,9 @@ func TestVectorDelete(t *testing.T) {
 	}
 
 	triple := deleteTriple(len(triples) - 2)
+	// after deleteing all vectors, we should get an empty array of vectors in response when we do silimar_to query
 	_, err = querySingleVectorError(t, strings.Split(triple, `"`)[1], "vtest", false)
-	require.NotNil(t, err)
+	require.NoError(t, err)
 }
 
 func TestVectorUpdate(t *testing.T) {

systest/vector/vector_test.go

@@ -288,3 +288,29 @@ func TestVectorIndexRebuilding(t *testing.T) {
 
 	testVectorQuery(t, gc, vectors, rdfs, pred, numVectors)
 }
+
+func TestVectorIndexOnVectorPredWithoutData(t *testing.T) {
+	conf := dgraphtest.NewClusterConfig().WithNumAlphas(1).WithNumZeros(1).WithReplicas(1).WithACL(time.Hour)
+	c, err := dgraphtest.NewLocalCluster(conf)
+	require.NoError(t, err)
+	defer func() { c.Cleanup(t.Failed()) }()
+	require.NoError(t, c.Start())
+
+	gc, cleanup, err := c.Client()
+	require.NoError(t, err)
+	defer cleanup()
+	require.NoError(t, gc.LoginIntoNamespace(context.Background(),
+		dgraphtest.DefaultUser, dgraphtest.DefaultPassword, x.GalaxyNamespace))
+
+	hc, err := c.HTTPClient()
+	require.NoError(t, err)
+	require.NoError(t, hc.LoginIntoNamespace(dgraphtest.DefaultUser,
+		dgraphtest.DefaultPassword, x.GalaxyNamespace))
+
+	require.NoError(t, gc.SetupSchema(testSchema))
+	pred := "project_discription_v"
+
+	vector := []float32{1.0, 2.0, 3.0}
+	_, err = gc.QueryMultipleVectorsUsingSimilarTo(vector, pred, 10)
+	require.NoError(t, err)
+}

tok/hnsw/helper.go

@@ -24,6 +24,7 @@ const (
 	DotProd              = "dotproduct"
 	plError              = "\nerror fetching posting list for data key: "
 	dataError            = "\nerror fetching data for data key: "
+	EmptyHNSWTreeError   = "HNSW tree has no elements"
 	VecKeyword           = "__vector_"
 	visitedVectorsLevel  = "visited_vectors_level_"
 	distanceComputations = "vector_distance_computations"

tok/hnsw/persistent_hnsw.go

@@ -289,10 +289,10 @@ func (ph *persistentHNSW[T]) calculateNewEntryVec(
 	})
 
 	if err != nil {
-		return 0, errors.Wrapf(err, "HNSW tree has no elements")
+		return 0, errors.Wrapf(err, EmptyHNSWTreeError)
 	}
 	if itr == 0 {
-		return itr, errors.New("HNSW tree has no elements")
+		return itr, errors.New(EmptyHNSWTreeError)
 	}
 
 	return itr, nil

worker/task.go

@@ -381,7 +381,7 @@ func (qs *queryState) handleValuePostings(ctx context.Context, args funcArgs) er
 				int(numNeighbors), index.AcceptAll[float32])
 		}
 
-		if err != nil {
+		if err != nil && !strings.Contains(err.Error(), hnsw.EmptyHNSWTreeError+": "+badger.ErrKeyNotFound.Error()) {
 			return err
 		}
 		sort.Slice(nnUids, func(i, j int) bool { return nnUids[i] < nnUids[j] })