fooMultiselectRequired lets you set a ui-select as required

foo-multiselect-required.js

/**
@memberof yourApp
@ngdoc directive
@name fooMultiselectRequired
@description ui-select does not handle required correctly when it's a multi-select, so here's a directive to fix that. See [this github issue](https://github.com/angular-ui/ui-select/issues/258) for more info. This directive is based on LeleDev's example, but adds an extra check.
@returns {boolean}
@example <ui-select multiple foo-multiselect-required name="whatever" ng-model="ctrl.payload.wahtever" theme="select2">
*/
(function(angular){
  'use strict';
  angular.module('yourApp').directive('fooMultiselectRequired', function($log){
    $log.log('fooMultiselectRequired directive is running.');
    return {
      restrict:'A',
      require:'ngModel',
      link:function(scope, elem, attrs, ngModel){
        ngModel.$validators.arrayRequired = function(modelValue, viewValue){
          return ((modelValue && modelValue.length > 0) ? true : false);
        };
      }
    };
  });
}(window.angular));