在 MongoDB 中使用 $ 运算符更新或插入文档

Question

I have a database where the general form of the documents look like so

    id: String,
    day: Number,
    counter: Number
    arrs: [{
        name: String,
        hr: Number,
        stuff: {}
    }]

So I will be creating/updating a new document for each new day and for each new hour and each name, so what I want to use is fineOneAndUpdate where I check if id is equal to an id, if the day is equal to the current day, if the hr is equal to the current hr, and if the name is equal to the object I want to update. Then, I want to increment stuff which can contain wildcard keys. So the query I currently have is this.

    Site.findOneAndUpdate({id: 123456, day: 1586390400, "arrs.hr": 16, "arrs.name": "Bob"},{
        $inc: {
            counter: 1,
            "arrs.$.stuff.${wildcardname}": 1
        }
    },
    {
        upsert: true
    }, function(err, result){
        if (err) {
            console.log(err)
        }
    });
}

So, if I have an empty db I expect to have this document after the query above

    id: 123456,
    day: 1586390400,
    counter: 1
    arrs: [{
        name: "Bob",
        hr: 16,
        stuff: {wildcardname: 1}
    }]

So if I were to run it again (within the same day + hr + name) with a different wildcardname I would then just update the document above so it would turn into

    id: 123456,
    day: 1586390400,
    counter: 2
    arrs: [{
        name: "Bob",
        hr: 16,
        stuff: {wildcardname: 1, wildcardname2: 1}
    }]

But I keep getting Error: The positional operator did not find the match needed from the query. . So after some investigating I found this in the docs

Do not use the positional operator $ with upsert operations because inserts will use the $ as a field name in the inserted document.

But I'm not entirely sure how else to do this otherwise. I don't want to have to make 2 calls to check if the document exists and create it, and another to update if it does exist.

Any help will be appreciated!

Answer 1

The $ operator refers to the specific array element that was matched by the query. If there was no document matched, then there was no element matched, so it can't really be expected to refer to anything.

If you are using MongoDB 4.2+ you can use the pipeline form of the update command and define a pipeline that will create the array if it doesn't exist, or find and update the element if it does. Upsert will pass the newly created document through the pipeline.

If you are using an older version, you'll need to run it as an update without upsert, and check the number of documents matched, then insert the document separately if nothing matched.