【mongoose】save方法报错

Question

数据如下：

{
    array: [
        {
            _id: 'aaa'
            sub_array: [
                {
                    _id: 'saaa',
                    name: 'aaa'
                },
                {...}
            ]
        },
        {...}
    ]
}

现在我要更新sub_array的name值：

Model.findOne({
    'array._id': 'aaa'
},{'array.$': 1}).then(respon=> {
    let checkdt = respon.array[0].sub_array.find((item)=> {
        reruen item._id == 'saaa'
    })
    checkdt.name = 'new val'
    respon.save().then(r=> res.send(r)).catch(er=> res.send(er))
})

结果报错：

{
    "message": "For your own good, using `document.save()` to update an array which was selected using an $elemMatch projection OR populated using skip, limit, query conditions, or exclusion of the _id field when the operation results in a $pop or $set of the entire array is not supported. The following path(s) would have been modified unsafely:\n  questions.0.sub_questions.1.score\n  questions.0.sub_questions.1.title\nUse Model.update() to update these arrays instead.",
    "name": "DivergentArrayError"
}

为什么会这样？我该怎么修改？

Answer 1

搜一下其实有人问过的：https://stackoverflow.com/que...
mongoose的github上也对这个问题有描述：issues#1334
简单地说，你用findOne的时候用了投影{'array.$': 1}，所以返回的文档中只有原始文档的一部分。而save方法是把你给的文档原样存回去，这显然不是你想要的结果，因为会丢数据。举例：

rs0:PRIMARY> db.test.insert({a: 1, b: 2})
WriteResult({ "nInserted" : 1 })
rs0:PRIMARY> db.test.find()
{ "_id" : ObjectId("5a741072979a928dbe90341a"), "a" : 1, "b" : 2 }
rs0:PRIMARY> var doc = db.test.findOne({}, {a: 1})
rs0:PRIMARY> db.test.save(doc)
WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })
rs0:PRIMARY> db.test.find()
{ "_id" : ObjectId("5a741072979a928dbe90341a"), "a" : 1 }

说白了，mongoose是在防止你自残，还是挺有节操的，业界良心。

Answer 2

你用的是mongoose?