验证一个值是否已经存在数据表中

airExpressApp.directive(‘validateCountry‘, function ($http, $q) {
    return {
        restrict: ‘AE‘,
        require: ‘ngModel‘,
        link: function ($scope, element, attributes, ngModelController) {
            ngModelController.$asyncValidators.countryExists = function (modelValue, viewValue) {
                var deferred = $q.defer();

                var obj = {};
                obj.Country_EN = modelValue;
                $http({
                    method: ‘POST‘,
                    url: ‘/Code/CountryByKey‘,
                    dataType: ‘json‘,
                    headers: {
                        ‘Content-Type‘: ‘application/json; charset=utf-8‘
                    },
                    data: JSON.stringify(obj),
                }).then(function (response) {
                    if (response.data.exists) {
                        deferred.resolve();
                    } else {
                        deferred.reject();
                    }
                });
                return deferred.promise;
            };
        }
    }
});