How to get child object from PSObject using dot notation string

Question

providing I have the following JSON

{
    "firstName":  "Frank",
    "lastName":  "Smith",
    "age":  "25",
    "address":  {
                    "streetAddress":  "21 3rd st",
                    "city":  "New York",
                    "state":  "NY",
                    "postalCode":  "10021"
                },
    "phoneNumber":  [
                        {
                            "type":  "home",
                            "number":  "212 555-1234"
                        },
                        {
                            "type":  "fax",
                            "number":  "646 555-4567"
                        }
                    ]
}

I need to be able to update a value using dotted notation.

$path = "C:\somePath\test.json"
$node = "address.streetAddress"         # should also work with "phoneNumber[0].number"
$value = "21 Jump St."

$config = Get-Content -Path $path -Raw | ConvertFrom-Json
$config.$node = $value
Write-Host $config.$node

#Set-Content $path $($config | ConvertTo-Json)

The problem I'm getting is that the property cannot be found.

Exception setting "address.streetAddress": "The property 'address.streetAddress' cannot be found on this object. Verify that the property exists and can be set."

What do I need to do to be able to pass in dotted notation, and update the appropriate value?

Keith Hill · Accepted Answer · 2015-01-12 18:56:09Z

4

While you can put a single property name in a variable and use that to access the property, you can't do that for multiple, dotted properties. You can work around this by using Invoke-Expression:

Invoke-Expression "`$config.$node = `$value"

answered Jan 12, 2015 at 18:56

Keith Hill

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1 Comment

Chase Florell Over a year ago

That's great, thanks. I didn't realize that's how it all came together.

DaFois · Accepted Answer · 2017-11-15 14:36:44Z

2

Shortest way around it is:

$config.$($node) = $value

Level of nesting does not matter, You can do this:

$config.$($node).$($subnode).$($subSubNode) = $value

You can also refer to properties in objects like this:

$config.$($node.nodename)=$value

edited Nov 15, 2017 at 14:36

DaFois

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answered Nov 15, 2017 at 13:54

Tomek

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