必须两次单击md按钮才能获得WebApi通话结果

Question

我正在尝试使用WebAPI调用和AngularJS构建一个简单的MVC WebApp。前端有一个md按钮，在控制器中定义了ng-click方法。每当我填满字段并单击按钮时，它应该转到angular Controller => factory =>调用Web Api并返回结果。但是，第一次单击后，什么也不会返回，但是如果我第二次单击同一按钮，它将获得我的数据。我不明白为什么会这样？

Index.cshtml

<md-button ng-click="GetResponse()" class="md-raised md-primary">
  Get Response
</md-button>

Controller.js

$scope.GetResponse = function () {
        debugger;

//Hardcodes the values, but still does not work
        $scope.edm.shortDescription = 'SDesc';
        $scope.edm.detailDescription = 'DDesc';
        $scope.edm.changeType = $("#ddlChangeType")[0].innerText;
        $scope.edm.category = 'CategoryName';
        $scope.edm.application = 'AppName';

        PrepareRequestService.GetFullRequest($scope.edm).then(function (d) {
                                                 $scope.fullRequest = d.data;
                                             }, function (e) {
                                                 alert('Failed');
                                             });

        console.log(JSON.stringify($scope.fullRequest));
//This is the line I am getting null first and then value after second click.
    }

Service.js

myAppModule.factory('PrepareRequestService', function ($http) {
    var fac = {};


    fac.GetFullRequest = function (edm) { 
        debugger;
//Here the Api Url is constructing properly
        console.log('http://localhost:17669/api/PrepareRequest/' + edm.shortDescription + '/'
                                                                       + edm.detailDescription + '/'
                                                                         + edm.changeType + '/'
                                                                         + edm.category + '/'
                                                                         + edm.application + '/');

//This is the actual call to API
        return $http.get('http://localhost:17669/api/PrepareRequest/' + edm.shortDescription + '/'
                                                              + edm.detailDescription + '/'
                                                                + edm.changeType + '/'
                                                                + edm.category + '/'
                                                                + edm.application + '/');


    };
    return fac;
});

Web API：

// GET: api/PrepareRequest/sDescription/dDescription/changeType/category/application
        public RootObject Get(string sDescription, string dDescription, string changeType, string category, string application)
        {
            RequestBuilder p = new RequestBuilder();

            RootObject ro = new RootObject();
            ro = p.PopulatePPMParameter(application, sDescription, "Today", "myName", changeType, category);
            return ro;

        }

///在浏览器中尝试时，此API返回了我第二次单击GetResponse后得到的确切JSON格式数据。但是我需要在每次点击中都做到这一点。