fixes #7486 (#7492)

* fixes #7486

* Added A test case for subset changes of model

* completed the test file for check_subset_model_change_test.go

schema/field.go

@@ -457,7 +457,7 @@ func (field *Field) setupValuerAndSetter() {
 	switch {
 	case len(field.StructField.Index) == 1 && fieldIndex > 0:
 		field.ValueOf = func(ctx context.Context, value reflect.Value) (interface{}, bool) {
-			fieldValue := reflect.Indirect(value).Field(fieldIndex)
+			fieldValue := reflect.Indirect(value).FieldByName(field.Name)
 			return fieldValue.Interface(), fieldValue.IsZero()
 		}
 	default:

tests/check_subset_model_change_test.go

@@ -0,0 +1,88 @@
+package tests_test
+
+import (
+	"fmt"
+	"strings"
+	"testing"
+
+	"gorm.io/gorm"
+)
+
+type Man struct {
+	ID     int
+	Age    int
+	Name   string
+	Detail string
+}
+
+// Panic-safe BeforeUpdate hook that checks for Changed("age")
+func (m *Man) BeforeUpdate(tx *gorm.DB) (err error) {
+	defer func() {
+		if r := recover(); r != nil {
+			err = fmt.Errorf("panic in BeforeUpdate: %v", r)
+		}
+	}()
+
+	if !tx.Statement.Changed("age") {
+		return nil
+	}
+	return nil
+}
+
+func (m *Man) update(data interface{}) error {
+	return DB.Set("data", data).Model(m).Where("id = ?", m.ID).Updates(data).Error
+}
+
+func TestBeforeUpdateStatementChanged(t *testing.T) {
+	DB.AutoMigrate(&Man{})
+	type TestCase struct {
+		BaseObjects Man
+		change      interface{}
+		expectError bool
+	}
+
+	testCases := []TestCase{
+		{
+			BaseObjects: Man{ID: 1, Age: 18, Name: "random-name"},
+			change: struct {
+				Age int
+			}{Age: 20},
+			expectError: false,
+		},
+		{
+			BaseObjects: Man{ID: 2, Age: 18, Name: "random-name"},
+			change: struct {
+				Name string
+			}{Name: "name-only"},
+			expectError: true,
+		},
+		{
+			BaseObjects: Man{ID: 2, Age: 18, Name: "random-name"},
+			change: struct {
+				Name string
+				Age int
+			}{Name: "name-only", Age: 20},
+			expectError: false,
+		},
+	}
+
+	for _, test := range testCases {
+		DB.Create(&test.BaseObjects)
+
+		// below comment is stored for future reference
+		// err := DB.Set("data", test.change).Model(&test.BaseObjects).Where("id = ?", test.BaseObjects.ID).Updates(test.change).Error
+		err := test.BaseObjects.update(test.change)
+		if strings.Contains(fmt.Sprint(err), "panic in BeforeUpdate") {
+			if !test.expectError {
+				t.Errorf("unexpected panic in BeforeUpdate for input: %+v\nerror: %v", test.change, err)
+			}
+		} else {
+			if test.expectError {
+				t.Errorf("expected panic did not occur for input: %+v", test.change)
+			}
+			if err != nil {
+				t.Errorf("unexpected GORM error: %v", err)
+			}
+		}
+	}
+}