Merge pull request #2 from tuan78/chore/flatten-nil-value

chore: handle flattening with nil value

csv_writer.go

@@ -7,9 +7,13 @@ import (
 
 // A CsvWriter writes records using CSV encoding.
 type CsvWriter struct {
-	Delimiter *rune // Field delimiter. If nil, it uses default value from csv.NewWriter
-	UseCRLF   bool  // True to use \r\n as the line terminator
-	writer    io.Writer
+	// Field delimiter. If nil, it uses default value from csv.NewWriter
+	Delimiter *rune
+
+	// True to use \r\n as the line terminator
+	UseCRLF bool
+
+	writer io.Writer
 }
 
 // NewCsvWriter returns a new CsvWriter that writes to w.

json_converter.go

@@ -7,8 +7,11 @@ import (
 
 // A ToCsvOption converts a JSON Array to CSV data.
 type ToCsvOption struct {
-	FlattenOption *FlattenOption // Set it to apply JSON flattening
-	BaseHeaders   CsvRow         // Base CSV headers used to add before dynamic headers
+	// Set it to apply JSON flattening
+	FlattenOption *FlattenOption
+
+	// Base CSV headers used to add before dynamic headers
+	BaseHeaders CsvRow
 }
 
 // ToCsv converts a JsonArray to CsvData with given op.

json_flattener.go

@@ -6,20 +6,53 @@ import (
 )
 
 const (
-	FlattenLevelUnlimited = -1 // Set it to FlattenOption.Level for unlimited flattening
-	FlattenLevelNonNested = 0  // Set it to FlattenOption.Level for non-nested flattening (equivalent to non-flattening)
+	// Set it to FlattenOption.Level for unlimited flattening.
+	FlattenLevelUnlimited = -1
+
+	// Set it to FlattenOption.Level for non-nested flattening
+	// (equivalent to non-flattening).
+	FlattenLevelNonNested = 0
+
+	// Set it to FlattenOption.Level for default level flattening
+	// (equivalent to FlattenLevelUnlimited).
+	FlattenLevelDefault = FlattenLevelUnlimited
 )
 
+// Set it to FlattenOption.Gap for default gap flattening.
+const FlattenGapDefault = "__"
+
 // A FlattenOption is for JSON object flattening.
 type FlattenOption struct {
-	Level     int    // Level of flattening, it can be FlattenLevelUnlimited, FlattenLevelNonNested or an int value in [1..n]
-	Gap       string // A gap between nested JSON and its parent JSON. It will be used when merging nested JSON's key with parent JSON's key
-	SkipMap   bool   // Skip Map type (typically JSON Object type) from flattening process
-	SkipArray bool   // Skip Array type (JSON array, string array, int array, float array, etc.) from flattening process
+	// Level of flattening, it can be FlattenLevelUnlimited,
+	// FlattenLevelNonNested or an int value in [1..n]
+	Level int
+
+	// A gap between nested JSON and its parent JSON.
+	// It will be used when merging nested JSON's key with parent JSON's key
+	Gap string
+
+	// Skip Map type (typically JSON Object type) from flattening process
+	SkipMap bool
+
+	// Skip Array type (JSON array, string array, int array, float array, etc.)
+	// from flattening process
+	SkipArray bool
 }
 
-// FlattenJsonObject flattens obj with given op.
+func DefaultFlattenOption() *FlattenOption {
+	return &FlattenOption{
+		Level: FlattenLevelDefault,
+		Gap:   FlattenGapDefault,
+	}
+}
+
+// FlattenJsonObject flattens obj with given op. If op is nil,
+// it will use op value from DefaultFlattenOption instead.
 func FlattenJsonObject(obj JsonObject, op *FlattenOption) {
+	if op == nil {
+		op = DefaultFlattenOption()
+	}
+
 	kset := make(map[string]struct{})
 	ks := make([]string, 0)
 	for k := range obj {
@@ -67,6 +100,8 @@ func extractJsonObject(k string, refval *reflect.Value, obj JsonObject, kset map
 			newK := fmt.Sprintf("%s[%v]", k, i)
 			extractJsonObject(newK, &nv, obj, kset, op, curLvl+1)
 		}
+	case reflect.Invalid:
+		obj[k] = nil
 	default:
 		obj[k] = refval.Interface()
 	}