Add WithSrcTag option.

copy.go

@@ -2,11 +2,12 @@
 package fieldmask_utils
 
 import (
+	"reflect"
+	"strings"
+
 	"github.com/pkg/errors"
 	"google.golang.org/protobuf/proto"
 	"google.golang.org/protobuf/types/known/anypb"
-	"reflect"
-	"strings"
 )
 
 // StructToStruct copies `src` struct to `dst` struct using the given FieldFilter.
@@ -71,16 +72,16 @@ func structToStruct(filter FieldFilter, src, dst *reflect.Value, userOptions *op
 
 		for i := 0; i < src.NumField(); i++ {
 			srcType := src.Type()
-			fieldName := srcType.Field(i).Name
-			dstName := dstKey(userOptions.DstTag, srcType.Field(i))
+			srcName := fieldName(userOptions.SrcTag, srcType.Field(i))
+			dstName := fieldName(userOptions.DstTag, srcType.Field(i))
 
-			subFilter, ok := filter.Filter(fieldName)
+			subFilter, ok := filter.Filter(srcName)
 			if !ok {
 				// Skip this field.
 				continue
 			}
 
-			srcField := src.FieldByName(fieldName)
+			srcField := src.Field(i)
 			if !srcField.CanInterface() {
 				continue
 			}
@@ -235,8 +236,12 @@ func structToStruct(filter FieldFilter, src, dst *reflect.Value, userOptions *op
 
 // options are used in StructToStruct and StructToMap functions to modify the copying behavior.
 type options struct {
+	// DstTag can be used to customize the dst field name according to the field's tag, i.g. json.
 	DstTag string
 
+	// SrcTag can be used to customize the src field name according to the field's tag, i.g. json.
+	SrcTag string
+
 	// CopyListSize can control the number of elements copied from src depending on src's Value
 	CopyListSize func(src *reflect.Value) int
 
@@ -267,6 +272,13 @@ func WithTag(s string) Option {
 	}
 }
 
+// WithSrcTag sets an option that gets the source field name from the field's tag.
+func WithSrcTag(s string) Option {
+	return func(o *options) {
+		o.SrcTag = s
+	}
+}
+
 // WithCopyListSize sets CopyListSize func you can set copy size according to src.
 func WithCopyListSize(f func(src *reflect.Value) int) Option {
 	return func(o *options) {
@@ -286,7 +298,8 @@ func newDefaultOptions() *options {
 	return &options{CopyListSize: func(src *reflect.Value) int { return src.Len() }}
 }
 
-func dstKey(tag string, f reflect.StructField) string {
+// fieldName gets the field name according to the field's tag, or gets StructField.Name default when the field's tag is empty.
+func fieldName(tag string, f reflect.StructField) string {
 	if tag == "" {
 		return f.Name
 	}
@@ -321,19 +334,19 @@ func structToMap(filter FieldFilter, src, dst reflect.Value, userOptions *option
 		}
 		srcType := src.Type()
 		for i := 0; i < src.NumField(); i++ {
-			fieldName := srcType.Field(i).Name
+			srcName  := fieldName(userOptions.SrcTag, srcType.Field(i))
 			if !isExported(srcType.Field(i)) {
 				// Unexported fields can not be copied.
 				continue
 			}
 
-			subFilter, ok := filter.Filter(fieldName)
+			subFilter, ok := filter.Filter(srcName)
 			if !ok {
 				// Skip this field.
 				continue
 			}
-			srcField := indirect(src.FieldByName(fieldName))
-			dstName := dstKey(userOptions.DstTag, srcType.Field(i))
+			srcField := indirect(src.Field(i))
+			dstName := fieldName(userOptions.DstTag, srcType.Field(i))
 			mapValue := indirect(dst.MapIndex(reflect.ValueOf(dstName)))
 			if !mapValue.IsValid() {
 				if srcField.IsValid() {
@@ -345,7 +358,7 @@ func structToMap(filter FieldFilter, src, dst reflect.Value, userOptions *option
 				}
 			}
 			if userOptions.MapVisitor != nil {
-				result := userOptions.MapVisitor(filter, src, mapValue, fieldName, dstName, srcField)
+				result := userOptions.MapVisitor(filter, src, mapValue, srcName, dstName, srcField)
 				if result.UpdatedDst != nil {
 					mapValue = *result.UpdatedDst
 

copy_test.go

@@ -3,12 +3,13 @@ package fieldmask_utils_test
 import (
 	"encoding/json"
 	"fmt"
-	"github.com/stretchr/testify/assert"
-	"github.com/stretchr/testify/require"
 	"reflect"
 	"testing"
 	"time"
 
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+
 	fieldmask_utils "github.com/mennanov/fieldmask-utils"
 )
 
@@ -2198,3 +2199,70 @@ func TestStructToStruct_CopyArraySizeAccordingFieldName(t *testing.T) {
 		Field2: [3]int{1, 2, 3},
 	}, dst)
 }
+
+func TestStructToStruct_WithSrcTag(t *testing.T) {
+	type A struct {
+		Field1 string
+		Field2 int `db:"some_field"`
+	}
+	type B struct {
+		Field1 string `struct:"a_name"`
+		A      A      `db:"another_name,omitempty"`
+	}
+	src := &B{
+		Field1: "B Field1",
+		A: A{
+			Field1: "A Field 1",
+			Field2: 1,
+		},
+	}
+	dst := &B{}
+	mask := fieldmask_utils.MaskFromString("Field1,A{Field2}")
+	err := fieldmask_utils.StructToStruct(mask, src, dst, fieldmask_utils.WithSrcTag("db"))
+	require.NoError(t, err)
+	assert.Equal(t, &B{Field1: src.Field1}, dst)
+
+	mask, _ = fieldmask_utils.MaskFromPaths([]string{"Field1", "another_name.some_field"}, func(s string) string { return s })
+	dst = &B{}
+	err = fieldmask_utils.StructToStruct(mask, src, dst, fieldmask_utils.WithSrcTag("db"))
+	require.NoError(t, err)
+	assert.Equal(t, &B{Field1: src.Field1, A: A{Field2: src.A.Field2}}, dst)
+}
+
+func TestStructToMap_WithSrcTag(t *testing.T) {
+	type A struct {
+		Field1 string
+		Field2 int  `db:"some_field1" json:"some_field1_json"`
+		Field3 bool `db:"some_field2" json:"some_field2_json"`
+	}
+	type B struct {
+		Field1 string `struct:"a_name"`
+		A      A      `db:"another_name,omitempty" json:"another_name_json"`
+	}
+	src := &B{
+		Field1: "B Field1",
+		A: A{
+			Field1: "A Field 1",
+			Field2: 1,
+		},
+	}
+	mask := fieldmask_utils.MaskFromString("Field1,A{Field2}")
+	dst := make(map[string]interface{})
+	err := fieldmask_utils.StructToMap(mask, src, dst, fieldmask_utils.WithTag("json"), fieldmask_utils.WithSrcTag("db"))
+	require.NoError(t, err)
+	assert.Equal(t, map[string]interface{}{
+		"Field1": src.Field1,
+	}, dst)
+
+	mask, _ = fieldmask_utils.MaskFromPaths([]string{"Field1", "another_name.some_field1", "another_name.some_field2"}, func(s string) string { return s })
+	dst = make(map[string]interface{})
+	err = fieldmask_utils.StructToMap(mask, src, dst, fieldmask_utils.WithTag("json"), fieldmask_utils.WithSrcTag("db"))
+	require.NoError(t, err)
+	assert.Equal(t, map[string]interface{}{
+		"Field1": src.Field1,
+		"another_name_json": map[string]interface{}{
+			"some_field1_json": src.A.Field2,
+			"some_field2_json": false,
+		},
+	}, dst)
+}