feat: NullIfEmptySlice transform (#470)

Author: graza-io

plugin/transform/primitives.go

@@ -17,7 +17,7 @@ import (
 	"github.com/turbot/go-kit/types"
 )
 
-///////////////////////
+// /////////////////////
 // Transform primitives
 // predefined transform functions that may be chained together
 
@@ -208,6 +208,19 @@ func NullIfZeroValue(_ context.Context, d *TransformData) (interface{}, error) {
 	return d.Value, nil
 }
 
+// NullIfEmptySliceValue returns nil if the input Value is an empty slice/array
+func NullIfEmptySliceValue(_ context.Context, d *TransformData) (interface{}, error) {
+	if d.Value == nil {
+		return nil, nil
+	}
+	v := helpers.DereferencePointer(d.Value)
+	b, l := reflect.TypeOf(v).Kind() == reflect.Slice, reflect.ValueOf(v).Len()
+	if b && l == 0 {
+		return nil, nil
+	}
+	return d.Value, nil
+}
+
 // UnmarshalYAML parse the yaml-encoded data and return the result
 func UnmarshalYAML(_ context.Context, d *TransformData) (interface{}, error) {
 	if d.Value == nil {

plugin/transform/primitives_test.go

@@ -793,6 +793,20 @@ Statement:
 		function: StringArrayToMap,
 		expected: "ERROR",
 	},
+	"NullIfEmptySlice array": {
+		d: &TransformData{
+			Value: []testStruct{{a: "A", b: "B"}, {a: "1", b: "2"}},
+		},
+		function: NullIfEmptySliceValue,
+		expected: []testStruct{{a: "A", b: "B"}, {a: "1", b: "2"}},
+	},
+	"NullIfEmptySlice nil": {
+		d: &TransformData{
+			Value: []testStruct{},
+		},
+		function: NullIfEmptySliceValue,
+		expected: nil,
+	},
 }
 
 func TestTransformFunctions(t *testing.T) {

plugin/transform/transform.go

@@ -95,3 +95,9 @@ func (t *ColumnTransforms) NullIfZero() *ColumnTransforms {
 	t.Transforms = append(t.Transforms, &TransformCall{Transform: NullIfZeroValue})
 	return t
 }
+
+// NullIfEmptySlice returns nil if the input value is an empty slice/array
+func (t *ColumnTransforms) NullIfEmptySlice() *ColumnTransforms {
+	t.Transforms = append(t.Transforms, &TransformCall{Transform: NullIfEmptySliceValue})
+	return t
+}