在mongoDB中的$投影findOneAndUpdate() [英] $ projection in mongoDB findOneAndUpdate()

问题描述

我正在尝试使用express和mongoose建立一个简单的任务队列.这个想法是获得一个客户，并返回广告系列ID和客户ID(这是Campaign的子文档).每次有人获取客户时，其状态代码都设置为1.我提出了以下查询:

I'm trying to build a simple task queue with express and mongoose. The idea is acquire a single client and return campaign id and client id (which is a subdocument of campaign). Each time someone acquires a client, its status code is set to 1. I've come up with the following query:

router.post('/lease', (err, res) => {
    Campaign.findOneAndUpdate({'isEnabled': true,  'clients.contact_status_code': 0}, {
            '$set': { 'clients.$.contact_status_code': 1 },
        },
        {
            new: true,
            projection: {
                'clients.$': true,
            },
        },
        (err, campaign) => {
            if (err) {
                return res.send(err);
            }

            res.json(campaign);
        }
    );
});

但是连接到此端点后，我所得到的就是:

But all i'm getting after connecting to this endpoint is this:

{"_id":"591483241a84946a79626aef","clients":[{},{}]}

在我看来，问题在于$投影，但我不知道如何解决此问题.

It seems to me that the problem is with the $ projection, but I have no idea how to fix this.

我尝试使用以下代码，利用$ elemMatch:

I tried using the following code, utilizing $elemMatch:

router.post('/lease', (err, res) => {
    Campaign.findOneAndUpdate({'isEnabled': true,  'clients.contact_status_code': 0}, {
            '$set': { 'clients.$.contact_status_code': 1 },
        },
        {
            new: true,
            projection: {
                clients: {
                    '$elemMatch': {contact_status_code: 1},
                }
            },
        },
        (err, campaign) => {
            if (err) {
                return res.send(err);
            }

            res.json(campaign);
        }
    );
});

不幸的是，每个请求都产生了集合中符合条件的第一个子文档，而不是特定于已更新的子文档.这是一个示例:

Unfortunately, each request yields the first subdocument in the collection, that matched the criteria -- not specifically the one that was updated. Here is an example:

说，我在mongo中有以下文件:

Say, i have the following document in mongo:

    {
    "_id" : ObjectId("591493d95d48e2738b0d4317"),
    "name" : "asd",
    "template" : "{{displayname}}",
    "isEnabled" : true,
    "clients" : [
            {
                    "displayname" : "test",
                    "_id" : ObjectId("591493d95d48e2738b0d4319"),
                    "contact_status_code" : 0
            },
            {
                    "displayname" : "client",
                    "_id" : ObjectId("591493d95d48e2738b0d4318"),
                    "contact_status_code" : 0
            }
    ],
    "__v" : 0

}

我第一次运行查询并获得以下结果:

I run the query for the first time and get the following result:

{"_id":"591493d95d48e2738b0d4317","clients":[{"displayname":"test","_id":"591493d95d48e2738b0d4319","contact_status_code":1}]}

通知客户端ID"591493d95d48e2738b0d4319"-这次它按预期运行.但是，当我第二次运行相同的查询时，尽管我希望得到一个ID为"591493d95d48e2738b0d4318"的对象，但我得到的对象完全相同.

Notice client id "591493d95d48e2738b0d4319" -- this time it runs as expected. But when i run the same query the second time, I get absolutely the same object, although I expect to get one with id "591493d95d48e2738b0d4318".

推荐答案

问题出在new: true

这是一个有效的示例:

Campaign.findOneAndUpdate({'isEnabled': true,  'clients.contact_status_code': 0}, {
            '$set': { 'clients.$.contact_status_code': 1 },
        },
        {
            //new: true <-- this was causing the trouble
            projection: {
                clients: {
                    '$elemMatch': {contact_status_code: 0}, // 0 because the old record gets matched
                },
            },
        },
        (err, campaign) => {
            if (err) {
                return res.send(err);
            }

            res.json(campaign);
        }
    );

我假设，当设置了new:true时，mongo会丢失匹配的上下文.不幸的是，这种方法返回了旧记录，但这仍然可以满足我获取_id的需求.

I assume, when the new:true is set, mongo loses the matching context. This approach returns the old record, unfortunately, but that still serves my needs to get the _id.

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