How to prevent user form ignoring suggestion in angularjs angular-ui-bootstrap uib-typeahead

I am using AngularJS v1.6.6 and angular-ui-bootstrap Version: 2.5.0 to create an autocomplete field.

It all works correctly but I need a way to be sure that the user actually selects the option from the list of suggestions.

Here is my code:

HTML:

<div class='container-fluid typeahead-demo' ng-controller="TypeaheadCtrl">
<h4>How to prevent user from typing the whole word ignoring suggestions?</h4>
<div>Model: 
<pre>{{selected | json}}</pre>
</div>
<form role="form" name="chooseStateForm" autocomplete="off" novalidate>
    <div class="form-group required">
        <div>
            <label for="state" class="control-label col-sm-3">Choose a State:</label>
                <input type="text" 
                        class="form-control" 
                        required 
                        placeholder="Try typing the whole name of the state ignoring suggestion" 
                        name="state" 
                        ng-model="selected" 
                        uib-typeahead="option as option.name for option in states | filter:{name: $viewValue}" 
                        typeahead-min-length="1" 
                        typeahead-no-results="noresults" 
                        typeahead-show-hint="true" 
                        >
        </div>
        <div ng-if="noresults">
        <p>No match found!</p>
        </div>
    </div>
</form>
<br><br><br><br>
<div>
    <button class="btn btn-primary" type="button" ng-click="$ctrl.ok()" ng-disabled="chooseStateForm.$invalid">OK</button>
    <button class="btn btn-primary" type="button" ng-click="$ctrl.cancel()">Cancel</button>
</div>

JS:

angular.module('app', ['ui.bootstrap']);
angular.module('app').controller('TypeaheadCtrl', function($scope) {

$scope.selected = undefined;
$scope.states = [
{id: 1, name: 'Alabama'},  
{id: 2, name: 'California'}, 
{id: 3, name: 'Delaware'}, 
{id: 4, name: 'Florida'}, 
{id: 5, name: 'Georgia'}, 
{id: 6, name: 'Hawaii'}, 
{id: 7, name: 'Idaho'},  
{id: 8, name: 'Kansas'}, 
{id: 9, name: 'Louisiana'}, 
{id: 10, name: 'Maine'}, 
{id: 11, name: 'Nebraska'}, 
{id: 12, name: 'Ohio'}, 
{id: 13, name: 'Pennsylvania'}, 
{id: 14, name: 'Rhode Island'}, 
{id: 15, name: 'South Carolina'}, 
{id: 16, name: 'Tennessee'},
{id: 17, name: 'Utah'}, 
{id: 18, name: 'Vermont'}, 
{id: 19, name: 'Washington'}
];
});

See this jsfiddle and you will understand what I mean: http://jsfiddle.net/elenat82/yhpbdvva/20/

If the user wants, for example, to choose Ohio, since it is only 4 letters he could find it easier to just type "Ohio" than to choose the suggested option.

But doing this my model becomes a string whilst it is an object if he chooses from the suggestions list.

Yes I check the validity of the model in my controller but I want it to be done before the user submits the form, I would like to show an error message explaining to the user what he did wrong.

---------- EDIT ----------

I found another way to achieve the same result but using a directive and extending the $validators object.

Here is the link to the updated jsfiddle: http://jsfiddle.net/elenat82/fL5fw1up/2/

And here is the updated code:

HTML:

<div class='container-fluid typeahead-demo' ng-controller="TypeaheadCtrl">
<h4>How to prevent user from typing the whole word ignoring suggestions?</h4>
<div>Model: 
<pre>{{selected | json}}</pre>
<div>Errors: 
<pre>{{chooseStateForm.state.$error | json}}</pre>
</div>
<form role="form" name="chooseStateForm" autocomplete="off" novalidate>
    <div class="form-group required">
        <div>
            <label for="state" class="control-label col-sm-3">Choose a State:</label>
                <input type="text" 
                        class="form-control" 
                        required 
                        placeholder="Try typing the whole name of the state ignoring suggestion" 
                        name="state" 
                        ng-model="selected" 
                        uib-typeahead="option as option.name for option in states | filter:{name: $viewValue}" 
                        typeahead-min-length="1" 
                        typeahead-no-results="noresults" 
                        typeahead-show-hint="true" 
                        object
                        >
        </div>
        <div ng-if="noresults">
        <p>No match found!</p>
        </div>
    </div>
</form>
<br><br><br><br>
<div>
    <button class="btn btn-primary" type="button" ng-click="$ctrl.ok()" ng-disabled="chooseStateForm.$invalid">OK</button>
    <button class="btn btn-primary" type="button" ng-click="$ctrl.cancel()">Cancel</button>
</div>

JS:

angular.module('app', ['ui.bootstrap']);
angular.module('app').controller('TypeaheadCtrl', function($scope) {

$scope.selected = undefined;
$scope.states = [
{id: 1, name: 'Alabama'},  
{id: 2, name: 'California'}, 
{id: 3, name: 'Delaware'}, 
{id: 4, name: 'Florida'}, 
{id: 5, name: 'Georgia'}, 
{id: 6, name: 'Hawaii'}, 
{id: 7, name: 'Idaho'},  
{id: 8, name: 'Kansas'}, 
{id: 9, name: 'Louisiana'}, 
{id: 10, name: 'Maine'}, 
{id: 11, name: 'Nebraska'}, 
{id: 12, name: 'Ohio'}, 
{id: 13, name: 'Pennsylvania'}, 
{id: 14, name: 'Rhode Island'}, 
{id: 15, name: 'South Carolina'}, 
{id: 16, name: 'Tennessee'},
{id: 17, name: 'Utah'}, 
{id: 18, name: 'Vermont'}, 
{id: 19, name: 'Washington'}
];
});


angular.module('app').directive('object', [function() {
return {
    restrict: 'A',
    scope: {},
    require: 'ngModel',
    link: function (scope, element, attrs, ngModel) {

        ngModel.$validators.object = function(modelValue,viewValue){
            if (angular.isObject(modelValue)) {
                return true;
            }
            else {
                return false;
            }
          };
    }
};

}
]);

You can add method for this validation for example:

$scope.isSelected = function() {
    return typeof $scope.selected == "object";
}