arrays - Mongoose 通过数组中的属性值拉取对象（可能为空）

Question

我正在尝试从 mongodb 数组中提取一个对象。

这是我的架构，

var VendorSchema = new Schema({

  _id: {
     type: Schema.Types.ObjectId,
     ref: "User"
  },
  service_orders: {
     pending_approval: [{
          service_order: {
              type: Schema.Types.ObjectId,
              ref: "ServiceOrder"
          },
          package: {
              type: Schema.Types.ObjectId,
              ref: "ServicePackage"
          }
     }]
  } 
)}

我的问题是，

 var marked_vendors =[ 5a76c4566b0e8c261cc47496, 5b05380f1cab52045c2afc1a ]

 Vendor.update({ '_id': { $in: marked_vendors } }, { $pull: { 'service_orders.pending_approval.service_order': req.body.serviceorder_id } }, { new: true }).exec(function(err, vendors) {
   if (err) {
        console.log(err);
        return res.json({ success: false, msg: err });
   } else {
        return res.json({ success: true, msg: 'Successfully pulled' });
   }
 });

但问题是，有时 'service_orders.pending_approval' 可能是一个空数组。它给了我以下错误

{
    "success": false,
    "msg": {
        "name": "MongoError",
        "message": "Cannot use the part (service_order) of (service_orders.pending_approval.service_order) to traverse the element ({pending_approval: []})",
        "driver": true,
        "index": 0,
        "code": 28,
        "errmsg": "Cannot use the part (service_order) of (service_orders.pending_approval.service_order) to traverse the element ({pending_approval: []})"
    }
}

不可能使用 try catch 块来跳过错误。那么有人可以帮我解决这个问题吗？

标签： arraysnode.jsmongodbmongoosepull