在仔细查看您的问题后，我发现您的 User 模型架构有问题.所以我相应地更新了答案.

After closely looking at your problem what I found is something wrong with your User Model schema. So I have updated the answer accordingly.

在您的 User 模型中，_carts 字段具有您使用的以下架构.

In your User model the _carts filed has following schema you have used.

_carts: [{
        type: Schema.Types.ObjectId,
        ref: 'cart'
    }]

因此，根据您的架构，该数组包含 Objectids，它引用了 cart 模型.(例如:_carts:[ObjectId1,ObjectId2,Object3 ....])

So as per your schema the array contains Objectids which has reference to cart model. (example: _carts:[ObjectId1,ObjectId2,Object3 ....])

但是在您的种子数据中，文档是

But in your Seed data the document is

const User1 = {
     _id: '1234',
     _carts: [{
              _id: '1',
              _product: {},
              quantity: 2
              }, 
              {
              _id: '2',
              _product: {},
              quantity: 4
              }],
        admin: false
    }

在 _carts 数组中有 objects.根据架构，它应该是 ObjectIds 而不是 Objects

which has objects in _carts array. As per schema it should be ObjectIds not Objects

现在根据您的查询 { $pull: { '_carts': { _id: (cart_id) }}} 您正在尝试提取具有 _id = cart_id 的文档代码>.但是您的 _carts 架构中没有 _id 可用.

Now as per your query { $pull: { '_carts': { _id: (cart_id) }}} you are trying to pull the document which has _id = cart_id. But there is no _id available in your _carts schema .

这是我的分析.如果您想在 carts 数组中存储 cart 详细信息.那么你的 User 模型的架构应该是

So here is my analysis. If you want store cart details in carts array. Then your User model's schema should be

_carts : [cartSchema]

否则您的 update 查询没有问题.它应该可以工作.

Otherwise your update query has no problem. It should work.

您提到的错误是由于 mongodb 连接问题造成的.请按照更新的 Mongoose 文档了解如何正确连接 Mongodb.

The error you have mentioned is due to mongodb connection issue. Please follow updated Mongoose doc on how to connect Mongodb properly.