Set a property on an Angular model from the controller

Question

I have some JSON that has two arrays of objects, one for "articles" and one for "allCategories". My controller is getting the data and assigning the two arrays to their own $scope as seen here:

$http.get(jsonFeed).success(function(response){
// JSON Data
$scope.articles = response.articles;
$scope.allCategories = response.allCategories;

Then I iterate over the allCategories array to populate my select in the view:

<div ng-app="newsArticleListing" ng-controller="articleListing">
<!--<p>PATH: {{ path }} URL: {{ url }} SEARCH: {{ urlQuery }} LOCATIONOJB: {{ locationObj }}</p> -->
    <form class="filter-form" method="get" name="Search" target="_top">
        <div class="filter-form-holder">
            <div class="filter-form-item">
                <span class="filter-form-label">Search by:</span>
            </div>
            <div class="filter-form-item">
                <div class="filter-form-select-wrapper">
                    <select class="directorySelect angularFilter"
                        ng-model="catSelect"
                        ng-options="cat.name for cat in allCategories | orderBy: 'name'"
                        ng-change="changeHandler()"
                        style="height:59px; width:385px; border-radius:0px;" >
                       <option value=''> All News</option>
                    </select>
                </div>
            </div>
                <input style="border-radius: 5px;" class="text-search" ng-model="courseTextSearch" type="text" name="search" placeholder="Search all listings"/>
        </div>
</form>

Then I iterate over the "articles" array and filter based off of the "catSelect" model, which is an object that contains { "name" : "somevalue", "filterValue" : "somevalue"} I am using "catSelect.filterValue"

<div class="container">
        <ul class="news-list">
        <li class="news-list-item" dir-paginate="article in articles | orderBy: '-date' | filter : { categories : catSelect.filterValue || undefined } | filter: courseTextSearch | itemsPerPage:pageSize" current-page="pagination.current">
        <article class="news-block" >
            <div ng-show="catChecker(catSelect.filterValue, article.categories)" class="news-block-holder is-blue">
            <strong class="news-block-taxonomy">{{ catSelect.name }}</strong>
            </div>
                <a class="news-block-img-link" href="{{ article.link }}" target="_blank">
                    <div class="news-block-img" style="background-image: url('{{ article.thumbImage }}'); background-size: cover;">
                        <img ng-src="{{ article.thumbImage }}" alt="{{ article.alt }}" />
                    </div>
                </a>
            <div class="news-block-body">
                <a class="news-block-link" ng-show="article.title" href="{{ article.link }}" target="_blank">{{ article.title }}</a>
           </div>
        </article>
        </li>
        </ul>
    </div>
    <!-- Paging -->
    <div class="pagePagination">
        <dir-pagination-controls max-size="8" direction-links="true">
        </dir-pagination-controls>
    </div>

Everything works fine, accept when I try to add in the ability to set the selected value from a query string. I can't assign the property "catSelect.filterValue" from within my controller as below: (fyi.. I have predefined some links currently that are in the structure "?

year=someyear&topics=sometopic")

if(window.location.href.includes('?'))
{
    var queryString = window.location.href.split('?');
    var values = queryString[1].split('&');
    var topics = values[1].split('=');
    var topic = topics[1];
    console.log(topic);
    if(topics[0] == "topics"){
        $scope.catSelect.filterValue = topics[1];
        console.log($scope.catSelect.filterValue);
    }
}

I thought because the model "catSelect" was two-way bound to the view I would have access to set the property of "$scope.catSelect.filterValue". What am I missing?