javascript - 额外选项和 ng-required

Question

我使用以下代码向我的选项列表添加一个额外的选项:

var defaultOption = { id: 0, descrip: 'Select Item Tree...' };
$scope.metaData.itemTrees.splice(0, 0, defaultOption);

现在，在某些情况下我希望需要项目树，所以我有

<div class="col-lg-9">
    <select class="form-control" name="itemTree" id="itemTree"
            ng-model="currentSalespoint.iTreeTop" ng-required="salespointMode.needsItemTree"
            ng-options="t.id as t.descrip for t in metaData.itemTrees"></select>
</div>
<div class="field-validation-error">
    <span ng-show="editSalespointGeneral.itemTree.$error.required && editSalespointGeneral.itemTree.$dirty">Item Tree selection is required.</span>
</div>

问题是 0 不应该是一个有效的选择，例如我无法将“选择项目树”保留为选定选项。我应该怎么做才能真正需要它？

如果我尝试使用 null 而不是 0，则会收到错误，但随后“Select ..”消失，下拉列表中出现空行。

Answer 1

解决方案之一是直接在html中定义空项目:

<select class="form-control" name="itemTree" id="itemTree"
        ng-model="currentSalespoint.iTreeTop" ng-required="salespointMode.needsItemTree"
        ng-options="t.id as t.descrip for t in metaData.itemTrees">
    <option value="">Select Item Tree...</option>
</select>

骗子:http://plnkr.co/edit/7m8YYVz7HNs1OY7hRIF1?p=preview