如何解析/访问 Powershell 4 中 Invoke-WebRequest 返回的 JSON

Question

I have the following call to an API in a powershell script (Powershell 4.0):

$Json = Invoke-WebRequest -Uri $RequestURL -UseBasicParsing -Headers $headers -ContentType  'application/json; charset=utf-8' -Method POST -Body $postParams -TimeoutSec 40 

...and the content of the response (which is a string in JSON format) is written to a file:

Set-Content $path -Value $Json.Content

An example of a typical response...

{
    "MyArray": [{
        "MyField": "A1",
        "MyField2": "A2"
    }, {
        "MyField": "B1",
        "MyField2": "B2"
    }]
}

All well and good, but now I have a requirement to parse the returned content as JSON and query some properties from within this Powershell script.

I presume I need to convert my string to 'proper' JSON and then to a powershell object in order to access the properties...so I have tried combinations of ConvertTo-Json and ConvertFrom-Json but can't ever seem to access it in anything other than a string. For example...

    $x = $Json.Content | ConvertTo-Json
    Write-Host $x.MyArray[0].MyField

    $y = $x | ConvertFrom-Json
    Write-Host $y[0].MyArray[0].MyField

In both cases above I get an error "Cannot index into a null array" suggesting that MyArray is null.

How do I convert my $Json response object into an object I can drill down into?

Answer 1

See ConvertFrom-Json

Converts a JSON-formatted string to a custom object or a hash table.

The ConvertFrom-Json cmdlet converts a JavaScript Object Notation (JSON) formatted string to a custom PSCustomObject object that has a property for each field in the JSON string.

Once you get the response converted to custom object or a hash table, you can access the individual properties

The link includes coding examples

Answer 2

This seems to work...

[void][System.Reflection.Assembly]::LoadWithPartialName("System.Web.Extensions")
    $x = (New-Object -TypeName System.Web.Script.Serialization.JavaScriptSerializer -Property @{MaxJsonLength=67108864}).DeserializeObject($Json.Content)
    Write-Host $x.MyArray[0].MyField

...although not sure why yet.