>>Looks like I got it although not 100% sure. Tired of debugging:
>>
>>

>> link: function ($scope, element, attrs, ngModel) {
>>               // if (element[0] && element[0].$touched) {
>>                    ngModel.$asyncValidators.smCodeUnique = function (modelValue, viewValue) {
>>
>>                        if (!viewValue || _.isEmpty(modelValue.trim())) {
>>                            return services.Q.when(true);
>>                        }
>>
>>                        var deferred = services.Deferred;
>>                        $log.info("Firing server-side validations for " + $scope.tableName + '.' + $scope.columnToTest);
>>                        let codeObject = {
>>                            id: $scope.primaryKey, tableName: $scope.tableName,
>>                            columnToTest: $scope.columnToTest, code: viewValue
>>                        };
>>                        return services.Http.put('api/items/checkCodeUniqueness', codeObject).then(
>>                            function (response) {
>>                                if (!response.data.isValid) {
>>                                    $scope.errorMessage = response.data.errorMessage;
>>                                    deferred.reject(response.data.errorMessage);
>>                                }
>>                                else {
>>                                    deferred.resolve(response.data);
>>                                }
>>                                return deferred.promise;
>>                            }
>>                        );
>>                    };
>>           //     }
>>            }

>Looks OK. but 'return deferred.promise' might be redundant ?

May be. The funny thing I realized few moments ago. I forgot about one extra scenario!!!!!!!! That simple scenario is when I am entering a new information. In this case nothing would prevent me (as of now) to enter same UPC and Barcode. I am wondering if I can simply handle this case before submitting and display error in a toaster then instead of trying an extra compare strings directive.

Will need something for case-insensitive string compare in JavaScript.

What do you think? Or should I be consistent and use another validator? And also, the scenario is even more complex for Matrix as there I am keeping an array of changed values, so I can potentially create many rows...

UPDATE. I was thinking I'll introduce objectToCompare inside that same directive. Do you think I can set both types of validators in one directive?