use nil instead of dummy implementation for transformation callback

Signed-off-by: pyalex <moskalenko.alexey@gmail.com>

go/cmd/server/main.go

@@ -17,10 +17,6 @@ const (
 	feastServerVersion  = "0.18.0"
 )
 
-func dummyTransformCallback(ODFVName string, inputArrPtr, inputSchemaPtr, outArrPtr, outSchemaPtr uintptr, fullFeatureNames bool) int {
-	return 0
-}
-
 // TODO: Add a proper logging library such as https://github.com/Sirupsen/logrus
 func main() {
 	repoPath := os.Getenv(flagFeastRepoPath)
@@ -45,7 +41,7 @@ func main() {
 	}
 
 	log.Println("Initializing feature store...")
-	fs, err := feast.NewFeatureStore(repoConfig, dummyTransformCallback)
+	fs, err := feast.NewFeatureStore(repoConfig, nil)
 	if err != nil {
 		log.Fatalln(err)
 	}

go/cmd/server/server_test.go

@@ -41,7 +41,7 @@ func getClient(ctx context.Context, basePath string) (serving.ServingServiceClie
 	if err != nil {
 		panic(err)
 	}
-	fs, err := feast.NewFeatureStore(config, dummyTransformCallback)
+	fs, err := feast.NewFeatureStore(config, nil)
 	if err != nil {
 		panic(err)
 	}

go/internal/feast/featurestore.go

@@ -19,10 +19,10 @@ import (
 )
 
 type FeatureStore struct {
-	config                *RepoConfig
-	registry              *Registry
-	onlineStore           OnlineStore
-	tranformationCallback TransformationCallback
+	config                 *RepoConfig
+	registry               *Registry
+	onlineStore            OnlineStore
+	transformationCallback TransformationCallback
 }
 
 // A Features struct specifies a list of features to be retrieved from the online store. These features
@@ -86,10 +86,10 @@ func NewFeatureStore(config *RepoConfig, callback TransformationCallback) (*Feat
 	registry.initializeRegistry()
 
 	return &FeatureStore{
-		config:                config,
-		registry:              registry,
-		onlineStore:           onlineStore,
-		tranformationCallback: callback,
+		config:                 config,
+		registry:               registry,
+		onlineStore:            onlineStore,
+		transformationCallback: callback,
 	}, nil
 }
 
@@ -189,22 +189,23 @@ func (fs *FeatureStore) GetOnlineFeatures(
 		result = append(result, vectors...)
 	}
 
-	onDemandFeatures, err := augmentResponseWithOnDemandTransforms(
-		requestedOnDemandFeatureViews,
-		requestData,
-		joinKeyToEntityValues,
-		result,
-		fs.tranformationCallback,
-		arrowMemory,
-		numRows,
-		fullFeatureNames,
-	)
-	if err != nil {
-		return nil, err
+	if fs.transformationCallback != nil {
+		onDemandFeatures, err := augmentResponseWithOnDemandTransforms(
+			requestedOnDemandFeatureViews,
+			requestData,
+			joinKeyToEntityValues,
+			result,
+			fs.transformationCallback,
+			arrowMemory,
+			numRows,
+			fullFeatureNames,
+		)
+		if err != nil {
+			return nil, err
+		}
+		result = append(result, onDemandFeatures...)
 	}
 
-	result = append(result, onDemandFeatures...)
-
 	result, err = keepOnlyRequestedFeatures(result, featureRefs, featureService, fullFeatureNames)
 	if err != nil {
 		return nil, err

go/internal/feast/featurestore_test.go

@@ -22,10 +22,6 @@ func getRegistryPath() map[string]interface{} {
 	return registry
 }
 
-func dummyTransformCallback(ODFVName string, inputArrPtr, inputSchemaPtr, outArrPtr, outSchemaPtr uintptr, fullFeatureNames bool) int {
-	return 0
-}
-
 func TestNewFeatureStore(t *testing.T) {
 	t.Skip("@todo(achals): feature_repo isn't checked in yet")
 	config := RepoConfig{
@@ -36,7 +32,7 @@ func TestNewFeatureStore(t *testing.T) {
 			"type": "redis",
 		},
 	}
-	fs, err := NewFeatureStore(&config, dummyTransformCallback)
+	fs, err := NewFeatureStore(&config, nil)
 	assert.Nil(t, err)
 	assert.IsType(t, &RedisOnlineStore{}, fs.onlineStore)
 }
@@ -62,7 +58,7 @@ func TestGetOnlineFeaturesRedis(t *testing.T) {
 		{Val: &types.Value_Int64Val{Int64Val: 1003}}}},
 	}
 
-	fs, err := NewFeatureStore(&config, dummyTransformCallback)
+	fs, err := NewFeatureStore(&config, nil)
 	assert.Nil(t, err)
 	ctx := context.Background()
 	response, err := fs.GetOnlineFeatures(

go/internal/feast/transformation.go

@@ -15,6 +15,12 @@ import (
 	"unsafe"
 )
 
+/*
+	TransformationCallback is a Python callback function's expected signature.
+	The function should accept name of the on demand feature view and pointers to input & output record batches.
+	Each record batch is being passed as two pointers: pointer to array (data) and pointer to schema.
+	Python function is expected to return number of rows added to the output record batch.
+*/
 type TransformationCallback func(ODFVName string, inputArrPtr, inputSchemaPtr, outArrPtr, outSchemaPtr uintptr, fullFeatureNames bool) int
 
 func augmentResponseWithOnDemandTransforms(