Unable to set the value when getting data from database angular JS dropdownlist MVC

See more:

C#

AngularJs

MVC5

I am unable to set the value of angular dropdownlist using mvc and rest api.
steps:
1. open the list page and select a record
2. navigate to another page where i can edit the selected record.

Issue:
when i navigate to page(edit page) 1st time the dropdown value is not set
when i go back to list page again and select record then dropdown value selected.
i am unable to understand what was wrong with it?

What I have tried:

HTML code:

<select ng-model="vm.CountryID">
                           <option ng-repeat="x in vm.country" value="{{x.countryID}}" ng-selected="{{x.countryID ==vm.CountryID}}" >{{x.countryName}}</option>
                       </select>

JS Code:

this.initializeController = function () {

           vm.title = "Customer Maintenance";

           vm.messageBox = "";
           vm.alerts = [];
           var city = new Object();
           ajaxService.ajaxPost(city, "api/CityService/GetCity", this.getCityOnSuccess, this.getCityOnError);
           var country = new Object();
           ajaxService.ajaxPost(country, "api/CountryService/GetCountry", this.getCountryOnSuccess, this.getCountryOnError);

           var customerID = ($routeParams.id || "");

           if (customerID === "") {
               vm.customerID = "0";
               vm.customerName = "";
               vm.customerAddress = "";
               vm.CountryID = "1";
               vm.CityID = "1";
               vm.phoneNo = "(+92) 300-8888888";
           }
           else {
               vm.customerID = customerID;
               var customer = new Object();
               customer.customerID = customerID;
               ajaxService.ajaxPost(customer, "api/CustomerService/GetCustomer", this.getCustomerOnSuccess, this.getCustomerOnError);
           }

       };

this.getCustomerOnSuccess = function (response) {
           vm.customerName = response.customerName;
           vm.customerAddress = response.customerAddress;
           vm.CityID = response.cityID;
           vm.CountryID = response.countryID;
           vm.phoneNo = response.phoneNo;

       };

this.getCountryOnSuccess = function (response) {
         vm.country = response.countries;

     };