angularjs如何实现联动并post?

最近在用AngularJs写下拉联动，但是困在了第二个下拉框值的显示和联动数值post的问题上，希望各位大神帮助

问题：

• 第二个下拉框值如何显示

• post提交后的值怎么处理？现在第一个下拉框post后的值是object:3，如何转化成json里的数值

html代码：

<div id="login" ng-app='angular_post_demo' ng-controller='sign_up'>
    <input type="text" size="40" ng-model="email">            
    <br>
    <input type="password" size="40" ng-model="password">
    <br>
    <select ng-options="universit.uni for universit in arr" ng-model="university"></select>
    <br>
    <select ng-options="student for university in arr" ng-model="student"></select>
    <br>
    <button ng-click="check_credentials()">Login</button>
    <br>
    <span id="message"></span>
</div>

js代码：

    var app = angular.module('angular_post_demo', []);
    app.controller('sign_up', function($scope, $http) {
        $scope.arr = [{
            "uni": "TS",
            "stu": ["Tom", "HHH", "KKK"]
        }, {
            "uni": "SDU",
            "stu": ["AA", "BBB"]
        }, {
            "uni": "SDUT",
            "stu": ["CCC", "DD"]
        }];
        $scope.university = $scope.arr[0];
        $scope.check_credentials = function() {
            document.getElementById('message').textContent = "";
            var request = $http({
                method: "post",
                url: window.location.href + "res.php",
                data: {
                    email: $scope.email,
                    pass: $scope.password,
                    university: $scope.university
                    // student: $scope.student
                }
            });
            request.success(function(data) {
                document.getElementById('message').textContent = data;
            });
        }
    });

---

• university的select加ngchange触发

• post的对象后处理具体看你什么语言