如何使用Powershell遍历JSON属性 [英] How to traverse JSON properties with Powershell

问题描述

我正在尝试使用Powershell访问JSON对象的特定属性值.不幸的是，我不知道结构中某些父级属性的键，因此我无法直接做到这一点.另外，由于JSON不是数组，因此无法通过索引位置访问.

I am trying to access a particular property value of a JSON object with Powershell. Unfortunately I do not know the keys of some of the parent properties within the structure, so I cannot do this in a straightforward way. Also as the JSON is not an array I am unable to access via index position.

上下文是，我正在从elasticsearch中查询正在运行的任务列表，并且需要获取任务的ID(我知道只有一个)，因此我可以进行后续调用以发现其完成状态.

The context is that I am querying a list of running tasks from elasticsearch and need to get the ID of the task (I know that there will only be one) so I can make subsequent calls to discover its completion status.

我已经研究了一些查询方法，但是不确定如何应用它们(PowerShell语法对我来说是相当新的东西.)

I've researched some querying methods but am unsure on how to apply them (PowerShell syntax is quite new to me).

我正在使用的JSON响应如下:

The JSON response I am working with looks like this;

  "nodes" : {
    "oTUltX4IQMOUUVeiohTt8A" : {
      "name" : "H5dfFeA",
      "transport_address" : "127.0.0.1:9300",
      "host" : "127.0.0.1",
      "ip" : "127.0.0.1:9300",
      "tasks" : {
        "oTUltX4IQMOUUVeiohTt8A:124" : {
          "node" : "oTUltX4IQMOUUVeiohTt8A",
          "id" : 124,
          "type" : "direct",
          "action" : "cluster:monitor/tasks/lists[n]",
          "start_time_in_millis" : 1458585884904,
          "running_time_in_nanos" : 47402,
          "cancellable" : false,
          "parent_task_id" : "oTUltX4IQMOUUVeiohTt8A:123"
        }
      }
    }
  }
}

使用这种给定的结构，我希望能够访问第一个任务"的ID属性.

With this given structure, I would like to be able to access the ID property of the first 'task'.

所以，如果我知道道具钥匙，那就是:

So if I knew the prop keys it would be:

nodes.oTUltX4IQMOUUVeiohTt8A.tasks.oTUltX4IQMOUUVeiohTt8A:124.id

如何在不事先知道键的情况下访问此值?

How can I access this value without knowing the keys beforehand?

非常感谢您的帮助.

谢谢 尼克

推荐答案

以下代码定义并使用函数Get-FirstPropertyValue ，该函数对第一个函数执行深度优先的递归搜索具有给定名称的对象图中的属性，并假定值非空，则返回其值:

The following code defines and uses function Get-FirstPropertyValue, which performs a recursive, depth-first search for the first property inside an object graph that has a given name and returns its value, assuming the value is non-null:

# Function that returns the value of the first property with the given 
# name found during recursive depth-first traversal of the given object.
# Note that null-valued properties are ignored.
function Get-FirstPropertyValue($obj, $propName) {
  $propNames = $obj.psobject.properties.Name
  if ($propName -in $propNames) {
    $obj.$propName
  } else {
    foreach ($iterPropName in $propNames) {
        if ($null -ne ($val = Get-FirstPropertyValue $obj.$iterPropName $propName)) {
          return $val
        }
      }
  }
}

# Input JSON
$json = @'
{
    "nodes": {
        "oTUltX4IQMOUUVeiohTt8A": {
            "name": "H5dfFeA",
            "transport_address": "127.0.0.1:9300",
            "host": "127.0.0.1",
            "ip": "127.0.0.1:9300",
            "tasks": {
                "oTUltX4IQMOUUVeiohTt8A:124": {
                    "node": "oTUltX4IQMOUUVeiohTt8A",
                    "id": 124,
                    "type": "direct",
                    "action": "cluster:monitor/tasks/lists[n]",
                    "start_time_in_millis": 1458585884904,
                    "running_time_in_nanos": 47402,
                    "cancellable": false,
                    "parent_task_id": "oTUltX4IQMOUUVeiohTt8A:123"
                }
            }
        }
    }
}
'@

# Convert the JSON to a [pscustomobject] graph with ConvertFrom-Json.
$objFromJson = $json | ConvertFrom-Json

# Using the function defined above, get the first 'tasks' object found
# during recursive depth-first traversal.
$tasks = Get-FirstPropertyValue $objFromJson 'tasks'

# Get the name of the resulting object's first property.
$propName = @($tasks.psobject.properties.Name)[0]

# Extract the .id property from the object stored in the first property.
$tasks.$propName.id

上面的结果:

124

---

更简洁，但更晦涩且可能更慢的选择是将JSON输入转换为XML，然后使用 XPath 对其进行查询:

---

A more concise, but more obscure and presumably slower alternative is to convert the JSON input to XML and then use XPath to query it:

# Input JSON
$json = @'
{
    "nodes": {
        "oTUltX4IQMOUUVeiohTt8A": {
            "name": "H5dfFeA",
            "transport_address": "127.0.0.1:9300",
            "host": "127.0.0.1",
            "ip": "127.0.0.1:9300",
            "tasks": {
                "oTUltX4IQMOUUVeiohTt8A:124": {
                    "node": "oTUltX4IQMOUUVeiohTt8A",
                    "id": 124,
                    "type": "direct",
                    "action": "cluster:monitor/tasks/lists[n]",
                    "start_time_in_millis": 1458585884904,
                    "running_time_in_nanos": 47402,
                    "cancellable": false,
                    "parent_task_id": "oTUltX4IQMOUUVeiohTt8A:123"
                }
            }
        }
    }
}
'@

$parent = 'tasks'
$prop = 'id'
$propType = 'int'

$json | 
  ConvertFrom-Json |
    ConvertTo-Xml -Depth ([int]::MaxValue) | 
      Select-Xml "//Property[@Name='$parent']/*/*[@Name='$prop']/text()" |
        ForEach-Object { $_.Node.InnerText -as $propType }

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