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属性的键,所以我不能直接这样做。此外,由于 JSON 不是数组,我无法通过索引位置访问。
上下文是我正在从 elasticsearch 查询正在运行的任务列表,需要获取任务的 ID(我知道只有一个),这样我就可以进行后续调用以发现其完成状态。
我研究了一些查询方法,但不确定如何应用它们(PowerShell 语法对我来说很新)。
我正在使用的 JSON 响应如下所示;
"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"
}
}
}
}
}
使用这个给定的结构,我希望能够访问第一个“任务”的 ID 属性。
因此,如果我知道 Prop 键,它将是:
nodes.oTUltX4IQMOUUVeiohTt8A.tasks.oTUltX4IQMOUUVeiohTt8A:124.id
如何在事先不知道 key 的情况下访问此值?
非常感谢任何帮助。
谢谢 尼克
最佳答案
以下代码定义并使用了函数Get-FirstPropertyValue
,它执行递归、深度优先搜索对象图中的第一个属性,该属性具有一个给定的名字并返回它的值,假设该值是非空的:
# 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
以上结果:
124
更简洁但更晦涩且可能更慢的替代方案是将 JSON 输入转换为 XML,然后使用 XPath 对其进行查询:
# 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 }
关于json - 如何使用 Powershell 遍历 JSON 属性,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/58477259/