angularjs不会将我的选项列表值发布到后端

Question

我有一个表格如下

        <form method="POST" name="addItem" role="form" ng-submit="saveAdd()">
        <div class="modal-header">
            <button type="button" class="close" data-dismiss="modal" aria-label="Close"><span aria-hidden="true">&times;</span></button>
            <h4 class="modal-title" id="myModalLabel">Create Item</h4>
        </div>
        <div class="modal-body">
            <div class="container">
                <div class="row">
                    <div class="col-xs-12 col-sm-6 col-md-6">
                    <strong>Category : </strong>
                        <div class="form-group">
                            <select ng-model="form.cid" placeholder="Category" name="cid" class="form-control" required >
                                <option value="1">abc</option>
                            </select>

                        </div>                      
                    </div>
                </div>
                <div class="row">
                    <div class="col-xs-12 col-sm-6 col-md-6">
                        <strong>Title : </strong>
                        <div class="form-group">
                            <input ng-model="form.title" type="text" placeholder="Name" name="title" class="form-control" required />
                        </div>
                    </div>
                    <div class="col-xs-12 col-sm-6 col-md-6">
                        <strong>Description : </strong>
                        <div class="form-group" >
                            <textarea ng-model="form.description" class="form-control" required>
                            </textarea>
                        </div>
                    </div>
                    <div class="col-xs-12 col-sm-6 col-md-6">
                        <strong>Alias : </strong>
                        <div class="form-group" >
                            <textarea ng-model="form.item_alias" class="form-control" required>
                            </textarea>
                        </div>
                    </div>                      
                </div>
                <button type="button" class="btn btn-default" data-dismiss="modal">Close</button>
                <button type="submit" ng-disabled="addItem.$invalid" class="btn btn-primary">Submit</button>
            </div>
        </div>
        </form>

并且angluarjs函数会将数据传递给laravel后端。

  $scope.saveAdd = function(){
    dataFactory.httpRequest('items','POST',{},$scope.form).then(function(data) {

      $scope.data.push(data);
      $(".modal").modal("hide");

    });
  }

laravel后端错误：

a foreign key constraint fails (`laravel_ang`.`items`, CONSTRAINT 
`items_cid_foreign` FOREIGN KEY (`cid`) REFERENCES `category` (`id`)) (SQL:
 insert into `items` (`title`, `description`, `item_alias`, `updated_at`,
 `created_at`) values (test, 123, 23, 2016-11-12 09:41:35, 2016-11-12 09:41:35))

在laravel路线上，它是一个资源控制器：

Route::resource('items', 'ItemController');

在控制器中，功能：

public function store(Request $request)
{
    $input = $request->all();

    $create = Item::create($input);
    return response($create);
}

在insert语句中包含cid的任何想法？