Merge pull request #967 from jackchenjc/issue-966

fix: Generate proper error message for 'unique' validation tag

common/validator.go

@@ -1,7 +1,7 @@
 //go:build !no_dto_validator
 
 //
-// Copyright (C) 2020-2024 IOTech Ltd
+// Copyright (C) 2020-2025 IOTech Ltd
 //
 // SPDX-License-Identifier: Apache-2.0
 
@@ -103,6 +103,13 @@ func getErrorMessage(e validator.FieldError) string {
 		msg = fmt.Sprintf("%s field should be one of %s", fieldName, fieldValue)
 	case "gt":
 		msg = fmt.Sprintf("%s field should greater than %s", fieldName, fieldValue)
+	case "unique":
+		// If the tag contains a field param, it means that the unique tag is used for a slice of struct
+		if fieldValue != "" {
+			msg = fmt.Sprintf("%s field should only contain unique elements with unique '%s' values", fieldName, fieldValue)
+		} else {
+			msg = fmt.Sprintf("%s field should only contain unique elements", fieldName)
+		}
 	case dtoDurationTag:
 		msg = fmt.Sprintf("%s field should follows the ISO 8601 Durations format, e.g.,100ms, 24h, or be greater than or equal to the minimum value %s ", fieldName, fieldValue)
 	case dtoUuidTag:

common/validator_test.go

@@ -0,0 +1,63 @@
+//
+// Copyright (C) 2025 IOTech Ltd
+//
+// SPDX-License-Identifier: Apache-2.0
+
+package common
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+type TestItem struct {
+	Name                string
+	UniqueArray         []string   `validate:"unique"`
+	UniqueSliceOfStruct []TestItem `validate:"unique=Name"` // only one field is supported
+}
+
+// The test only covers the validation of the "unique" tag at the time of writing this comment.
+// TODO: Add more tests to cover other validation tags if needed
+
+// TestValidate tests the Validate function
+func TestValidate(t *testing.T) {
+
+	validUniqueArray := TestItem{
+		UniqueArray: []string{"a", "b", "c"},
+	}
+	invalidUniqueArray := TestItem{
+		UniqueArray: []string{"a", "a", "c"},
+	}
+	validUniqueSliceOfSturct := TestItem{
+		UniqueSliceOfStruct: []TestItem{
+			{Name: "a"},
+			{Name: "b"},
+		},
+	}
+	invalidUniqueSliceOfSturct := TestItem{
+		UniqueSliceOfStruct: []TestItem{
+			{Name: "a"},
+			{Name: "a"},
+		},
+	}
+
+	tests := []struct {
+		name     string
+		input    any
+		expected bool
+	}{
+		{"valid, unique tag for arrays and slices", validUniqueArray, false},
+		{"invalid, unique tag for arrays and slices", invalidUniqueArray, true},
+		{"valid, unique tag for slices of struct", validUniqueSliceOfSturct, false},
+		{"invalid, unique tag for slices of struct", invalidUniqueSliceOfSturct, true},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			err := Validate(tt.input)
+			if tt.expected {
+				require.Error(t, err)
+			}
+		})
+	}
+}