Angularjs material or angularjs store multiple sel

I am using Angular material and I am stuck on multi selection dropdown , where I was selecting more than one options and on ng-change I am calling function which will get id of every option and I will compare API id but As I select it will provide data in function like In first option selection 123456 In second option selection 123456,456231

In Third option selection 123456,456231,471258

so whenever I do compare It goes inside the condition only once and not more even I tried to split It gives error and do nothing.

<md-select ng-model="$parent.follower" placeholder="Select Person" multiple="true" ng-change="getFollowers(follower)">             
     <md-option ng-repeat="follower in followers" value="{{follower.id}}"> {{follower.full_name}}</md-option>
   </md-select>

So Let me know how to handle this situation, if anyone have experience and very well Please let me know.

Thanks Shivam

I have created Codepen for you where you can see the value changing each time As I dont know you data format I used a demo one

HTML

<div ng-controller="AppCtrl as ctrl" class="md-padding selectdemoBasicUsage" ng-app="MyApp">
  <div>
    <h1 class="md-title">Enter an address</h1>
    <div layout="row">
      <md-input-container>
        <label>Street Name</label>
        <input type="text">
      </md-input-container>
      <md-input-container>
        <label>City</label>
        <input type="text">
      </md-input-container>
      <md-select placeholder="State" ng-model="ctrl.userState" multiple="true" ng-change='changeValue(ctrl.userState)'>
        <md-option ng-repeat="state in ctrl.states" value="{{state.abbrev}}">{{state.abbrev}}</md-option>
      </md-select>
    </div>
  </div>
</div>

Angularjs Code

      'use strict';
      angular
          .module('MyApp')
          .controller('AppCtrl', function($scope,$http) {
            this.userState = '';
            this.states = ('AL AK AZ AR CA CO CT DE FL GA HI ID IL IN IA KS KY LA ME MD MA MI MN MS ' +
                'MO MT NE NV NH NJ NM NY NC ND OH OK OR PA RI SC SD TN TX UT VT VA WA WV WI ' +
                'WY').split(' ').map(function (state) { return { abbrev: state }; });
     $scope.changeValue=function(value){
        console.log(value);
     $http.post(//url).then(function(response){
//handle response here
     });
  }    
  });

Codepen for working solution http://codepen.io/anon/pen/WvygLZ