mongoDB:为添加到数组字段的每个新子项创建一个 ObjectId [英] mongoDB : Creating An ObjectId For Each New Child Added To The Array Field

问题描述

mongodb 2.1.4(节点驱动)

mongodb 2.1.4(The Node Driver)

我目前正在尝试为我插入到数组中的每条消息创建一个新的 ObjectID(该数组是一个子文档).

I'm currently trying to create a new ObjectID for each message I insert into an array(the array being a subdocument).

我是这样理解的 - 可以轻松地对数组中的每条消息执行所有 CRUD 操作.

I figure this way - All CRUD operations can easily be performed on each message in the array.

例如:

线程"集合(注意 - 每条消息的 ObjectId)

The "threads" collection(Note- An ObjectId for each message)

{
    "_id": ObjectId("1234132413424123"), //A thread id
    messages:[
        {
            _id :ObjectId("134124412341234"),// A message id
            "message":"MongoDB is my friend"

        },
        {
            _id :ObjectId("534124412342377"),
            "message":"MongoDB is my friend too"

        },
        ...
    ]
},
{
    "_id": ObjectId("22341324134224234"),
    messages:[
        {
            _id :ObjectId("8341244123411235"),
            "message":"Something clever"

        },
        {
            _id :ObjectId("134124412342376"),
            "message":"blah blah blah"

        },
        ...
    ]
}

我现在在做什么:

var query = {};

query["_id"] = new ObjectID(threadID);

var update = {$push: {}};    //I write the update object externally just for aesthetics

update.$push["messages"] = newMessage; 

var threadsCollection = db.collection('threads');
threadsCollection.findOneAndUpdate(query,update, function (err, result) {
    if (err) {
        console.log(err);
    } 
    db.close();
});

问题:

与集合的插入"不同，使用 $push 的更新不会创建添加到数组中的每条消息的新 ObjectId.

Unlike "insert" for collections, an update with $push does not create a new ObjectId for each message added to the array.

问题:

是否有在 $push into 期间创建 ObjectID 的标准方法子数组?还是我们应该手动创建一个 ObjectID 并事先将其添加到孩子?

Is there a standard way of creating an ObjectID during a $push into the child array? Or should we just manually create an ObjectID and add it to the child beforehand?

推荐答案

不是 mongodb 专家，但如果我理解正确，您希望自动插入子文档的 _id 字段.

Not a mongodb expert but, if I understand you correctly, you wish the _id field of the subdocument to be inserted automatically.

我创建了 threads db，然后使用以下命令将第一个 message 插入到 messages 集合中:

I created threads db and then inserted the first message in the messages collection using the following command:

db.messages.insert({messages:[{_id:ObjectId(), message:"Message 1."}]}); 

注意 _id:ObjectId() 字段.结果如下:

Notice the _id:ObjectId() field. The result is as follow:

现在我有了一个 ObjectId(56...)，我可以更新该特定记录并向其中插入更多消息.命令如下:

Now that I have an ObjectId(56...), I can update that particular record and insert more messages to it. And the command is as follow:

db.messages.update({"_id":ObjectId("56...")}, 
{$push:{messages:{_id:ObjectId(), message:"I am message 2."}}});

以上将在集合中插入新消息.请参阅以下屏幕截图:

And the above would insert the new message in the collection. See below screenshots:

最后经过几次更新后，集合如下所示:

and finally after a few updates the collection looks as follow:

messages 数组中的所有 _id 字段都是自动生成的.

All the _id fields in the messages array are automatically generated.

出于各种原因，使用 _id 字段可能不是一个好主意.有关是否使用 _id 作为子文档的键的更多详细信息，请谷歌.

It might not be a good idea to use _id fields for various reasons. Please Google for more details on whether to use _id as key for subdocuments or not.

我使用 MongoDB shell 版本 3.0.6 作为命令.

编辑 28-01-2016 16:09

由于上述解决方案是基于 MongoDB shell，我决定使用 Node.js 驱动程序对 MongoDB 进行另一个测试.首先，我声明 ObjectID 变量如下

Since the above solution was based on MongoDB shell, I decided to do another test using Node.js driver for MongoDB. First of all, I declare ObjectID variable as follow

var ObjectID = require('mongodb').ObjectID;

我将在我的 update 和 findOneAndUpdate 函数调用中使用 ObjectID 和应该插入消息的线程的文档 ID

I will use the ObjectID with document id of the thread to which the message should be inserted as follow in my update and findOneAndUpdate function calls

app.get('/insertNewMessage', function(req, res) {
    db.collection("messages").findOneAndUpdate({
        _id: new ObjectID('56aa3554e90911b64c36a424')
    }, {
        $push: {
            messages: {
                _id: new ObjectID(),
                message: "From NodeJS with <3 using findOneAndUpdate.Bye."
            }
        }
    }, function(err, result) {
        if (err)
            res.json(err);
        else
            res.json(result);
    });
});

两者都测试过，效果很好.请看下面的截图:

Tested both and works just fine. See the screenshot below:

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