fix: Add validation tag to verify subscription with empty Channels

Add validation tag `gt=0` to verify subscription:
- empty Channels should be invalid
- nil Channels should be valid

Close #565

Signed-off-by: weichou <weichou1229@gmail.com>

v2/dtos/requests/subscription_test.go

@@ -211,6 +211,10 @@ func TestUpdateSubscriptionRequest_Validate(t *testing.T) {
 	unsupportedChannelType.Subscription.Channels = []dtos.Address{
 		dtos.NewMQTTAddress("host", 123, "publisher", "topic"),
 	}
+	validWithoutChannels := NewUpdateSubscriptionRequest(updateSubscriptionData())
+	validWithoutChannels.Subscription.Channels = nil
+	invalidEmptyChannels := NewUpdateSubscriptionRequest(updateSubscriptionData())
+	invalidEmptyChannels.Subscription.Channels = []dtos.Address{}
 
 	categoryNameWithReservedChar := NewUpdateSubscriptionRequest(updateSubscriptionData())
 	categoryNameWithReservedChar.Subscription.Categories = []string{namesWithReservedChar[0]}
@@ -239,6 +243,8 @@ func TestUpdateSubscriptionRequest_Validate(t *testing.T) {
 		{"invalid, category name containing reserved chars", categoryNameWithReservedChar, true},
 		{"invalid, receiver name containing reserved chars", receiverNameWithReservedChars, true},
 		{"invalid, resendInterval is not specified in ISO8601 format", invalidResendInterval, true},
+		{"valid, without channels", validWithoutChannels, false},
+		{"invalid, empty channels", invalidEmptyChannels, true},
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {

v2/dtos/subscription.go

@@ -29,7 +29,7 @@ type Subscription struct {
 type UpdateSubscription struct {
 	Id             *string   `json:"id,omitempty" validate:"required_without=Name,edgex-dto-uuid"`
 	Name           *string   `json:"name,omitempty" validate:"required_without=Id,edgex-dto-none-empty-string,edgex-dto-rfc3986-unreserved-chars"`
-	Channels       []Address `json:"channels,omitempty" validate:"omitempty,dive"`
+	Channels       []Address `json:"channels,omitempty" validate:"omitempty,gt=0,dive"`
 	Receiver       *string   `json:"receiver,omitempty" validate:"omitempty,edgex-dto-none-empty-string,edgex-dto-rfc3986-unreserved-chars"`
 	Categories     []string  `json:"categories,omitempty" validate:"omitempty,dive,gt=0,edgex-dto-none-empty-string,edgex-dto-rfc3986-unreserved-chars"`
 	Labels         []string  `json:"labels,omitempty" validate:"omitempty,dive,edgex-dto-none-empty-string,edgex-dto-rfc3986-unreserved-chars"`