AngularJS-麻烦设置默认下拉菜单选项

我是AngularJS的新手。现在，我在电子商务网站上应用了以下两个过滤器：

                         <div ng-show="user.ShipMethod != null && shippers && orderShipAddress.AddressName != 'BIG'" " ng-class="{'view-form-select': !currentOrder.LineItems[0].ShipperName, '': currentOrder.LineItems[0].ShipperName }">
                                <label ng-class="{required: !currentOrder.IsMultipleShip() && user.ShipMethod != null}" ng-show="currentOrder.LineItems[0].ShipperName || !currentOrder.IsMultipleShip() && user.ShipMethod != null">{{('Shipping' | r) + ' Method' | xlat}}</label>
                                <select class="form-control" ng-change="updateShipper()" name="shipMethod"
                                        ng-model="currentOrder.LineItems[0].ShipperName"
                                        ng-show="user.ShipMethod.ShipperSelectionType == 'UserDropDown'"
                                        ng-options="shipper.Name as (shipper.Name + ' ' + (shipper.ShippingRate.Price | currency | xlat)) for shipper in shippers | filter: { Name: '!Pick-Up at BIG'}"
                                        ng-required="!currentOrder.IsMultipleShip() && user.ShipMethod != null" >

                                    <option value=""></option>
                                </select>
                                <i class="fa fa-truck"></i>
                            </div>

                            <div ng-show="user.ShipMethod != null && shippers && orderShipAddress.AddressName == 'BIG'" ng-class="{'view-form-select': !currentOrder.LineItems[0].ShipperName, '': currentOrder.LineItems[0].ShipperName }">
                                <label ng-class="{required: !currentOrder.IsMultipleShip() && user.ShipMethod != null}" ng-show="currentOrder.LineItems[0].ShipperName || !currentOrder.IsMultipleShip() && user.ShipMethod != null">{{('Shipping' | r) + ' Method' | xlat}}</label>
                                <select class="form-control" ng-change="updateShipper()" name="shipMethod"
                                        ng-model="currentOrder.LineItems[0].ShipperName"
                                        ng-show="user.ShipMethod.ShipperSelectionType == 'UserDropDown'"
                                        ng-options="shipper.Name as (shipper.Name + ' ' + (shipper.ShippingRate.Price | currency | xlat)) for shipper in shippers | filter: { Name: 'Pick-Up at BIG'}"
                                        ng-required="!currentOrder.IsMultipleShip() && user.ShipMethod != null" >
                                    <option value=""></option>
                                </select>
                                <i class="fa fa-truck"></i>
                            </div>
                        </div>

我的控制器位于这里：https : //big.four51ordercloud.com/test0530/js/directives/ordershipping.js

在我的控制器中，我想出了这个选项来设置默认的下拉菜单选项，但是我不确定将其放在updateShipper（）函数中的哪个位置。如果下拉菜单中只有1个选项，我希望它为默认设置。现在，如果有1个选项，则用户必须手动选择它，但是其他选项可能会填充，具体取决于是否满足其他过滤器的条件。您看到的第一个过滤器将始终在下拉列表中产生多个选项，而第二个过滤器将始终仅产生一个选项-“ BIG上车”选项。

$scope.currentOrder.LineItems[0].ShipperName = $scope.shippers[0];