Form element reference in AngularJS controller

I have a html file with 2 buttons outside the form. The idea is that when a button is clicked, the form will be shown and the form element “role_id” will be set to a passed value of 1 or 2. I cannot figure out the code to include inside the controller to set the value of role_id. Can you please help?
Index.html

<button class="btn btn-custom" ng-click="formToggle(1)" > Add Role 1</button>
<button class="btn btn-custom" ng-click="formToggle(2)"> Add Role 2</button>
<form class="form-horizontal" name="persForm" id="persForm" ng-submit="insertInfo(persInfo);" >
    <input type="hidden" name="role_id" id="role_id" class="form-control" ng-model="persInfo.role_id" value="" />
</ form>

Controller.js

var crudApp = angular.module('crudApp',[]);
crudApp.controller("DbController",['$scope','$http', function($scope,$http){
    $scope.formToggle = function(id){
        $('#persForm').slideToggle();
        //Code here to set form element ‘role_id’ to id
    }
}]);

I’ve tried getElementById and other javascript DOM methods but it doesn’t seem to work inside AngularJS.