$ push等价于mongo中的地图 [英] $push equivalent for map in mongo

问题描述

我们可以使用$push(向数组中添加元素)更新为atomically update包含数组的单个文档

We can use $push (to add an element into an array) in update to atomically update a single document containing the array

但是，我找不到原子地add a new key到文档中地图的方法.

However, I could not find a way to atomically add a new key to a map in a document.

我可以

* read the document,
* read the map in it, 
* update the map in my code and 
* update the document in my code.

但这不是原子的.

But that is not atomic.

我只处理single document，但是该文档具有地图.

I am only dealing with a single document but that document has a map.

有没有办法自动更新(add a new key)地图?

Is there a way I can update (add a new key) map atomically?

推荐答案

> $set 的>点符号 > 运算符是处理单个元素的方式.

Dot notation with the $set operator is how you address individual elements.

获取以下文档:

{
    "_id": 1,
    "map": {
        "field2": 1
    }

}

要在地图上添加"field3"，您需要像这样进行更新:

In order to add "field3" to the map you update like this:

db.collection.update({ "_id": 1 }, { "$set": { "map.field3": 2 } })

所以现在您的文档看起来像这样:

So now your document looks like this:

{
    "_id": 1,
    "map": {
        "field2": 1,
        "field3": 2
    }
}

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