AngularJs injecting factory into controller

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AngularJs

Dears ,

I'm trying to do the following :

var common = angular.module('common', ['ui.bootstrap']);

var app = angular.module('app', ['common']);


(function (cr) {
    var modelHelper = function () {
        var self = this;
        self.getObjectById = function (object, key, value) {
            angular.forEach(object, function (objKey, objValue) {
                var a = 0;
            });
            return undefined;
        };
    };
    cr.modelHelper = modelHelper;
}(window.sys));


dgitCommon.factory('modelHelper', function () {
    return sys.modelHelper();
});

and its not injecting the 'modelHelper' into the controller like bellow :

app.controller("xController", function ($scope, $modal, modelHelper) {

});

Thanks in advance .