无法使用零件(...)遍历元素 [英] cannot use the part (...) to traverse the element

问题描述

运行mongod 3.6并尝试使用此示例.

Running mongod 3.6 and attempting to use this example.

以下是示例数据:

> db.students2.find().pretty()
{
    "_id" : 1,
    "grades" : [
        {
            "grade" : 80,
            "mean" : 75,
            "std" : 8
        },
        {
            "grade" : 85,
            "mean" : 90,
            "std" : 6
        },
        {
            "grade" : 85,
            "mean" : 85,
            "std" : 8
        }
    ]
}
{
    "_id" : 2,
    "grades" : [
        {
            "grade" : 90,
            "mean" : 75,
            "std" : 8
        },
        {
            "grade" : 87,
            "mean" : 90,
            "std" : 5
        },
        {
            "grade" : 85,
            "mean" : 85,
            "std" : 6
        }
    ]
}

我尝试使用示例中指定的所有位置运算符:

I am attempting to use the all positional operator as specified in the example:

> db.students2.update({}, { $inc: { "grades.$[].std" : -2 } }, {multi: true})
WriteResult({
    "nMatched" : 0,
    "nUpserted" : 0,
    "nModified" : 0,
    "writeError" : {
        "code" : 16837,
        "errmsg" : "cannot use the part (grades of grades.$[].std) to traverse the element ({grades: [ { grade: 80.0, mean: 75.0, std: 8.0 }, { grade: 85.0, mean: 90.0, std: 6.0 }, { grade: 85.0, mean: 85.0, std: 8.0 } ]})"
    }
})

为什么会出现此错误消息?我没有正确遵循文档吗?

Why is this error message occurring? Am I not following the documentation properly?

推荐答案

当从mongodb的较低版本切换到较高版本时，必须设置

When switching from lower version to higher version for mongodb you have to set setFeatureCompatibilityVersion for your mongodb which

启用或禁用保留与以下数据不兼容的数据的功能 MongoDB的早期版本.您只能发出 针对管理员数据库的setFeatureCompatibilityVersion.

Enables or disables the features that persist data incompatible with earlier versions of MongoDB. You can only issue the setFeatureCompatibilityVersion against the admin database.

您可以通过在mongo shell中运行此命令来简单地进行设置

You can simply set this by running this command in mongo shell

db.adminCommand( { setFeatureCompatibilityVersion: "3.6" } )

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