Possible to pull info from AdditionalProperties dictionary with Microsoft Graph PowerShell cmdlets?

Given the following $object, 3 properties and one of them AdditionalProperties is a Dictionary<TKey,TValue>:

$dict = [Collections.Generic.Dictionary[object, object]]::new()
$dict.Add('displayName', 'placeholder')
$dict.Add('mail', 'placeholder')
$dict.Add('userPrincipalName', 'placeholder')

$object = [pscustomobject]@{
    DeletedDateTime      = 'placeholder'
    Id                   = 'placeholder'
    AdditionalProperties = $dict
}

Supposing from this object you're interested in Id, displayName and mail, you could use Select-Object with calculated properties:

$object | Select-Object @(
    'Id'
    @{
        Name       = 'displayName'
        Expression = { $_.additionalProperties['displayName'] }
    }
    @{
        Name       = 'mail'
        Expression = { $_.additionalProperties['mail'] }
    }
)

However this gets messy as soon as you need to pick more property values from the objects, PSCustomObject with a loop comes in handy in this case:

$object | ForEach-Object {
    [pscustomobject]@{
        Id          = $_.Id
        displayName = $_.additionalProperties['displayName']
        mail        = $_.additionalProperties['mail']
    }
}

Both alternatives would output the same "flattened" object that can be converted to Csv without any issue:

• As Object

Id          displayName mail
--          ----------- ----
placeholder placeholder placeholder

• As Csv

"Id","displayName","mail"
"placeholder","placeholder","placeholder"

In that sense, you could construct an array of objects using one of the above techniques, for example:

Get-MgGroupMember -GroupId $GroupID | ForEach-Object {
    [pscustomobject]@{
        Id                = $_.id
        displayName       = $_.additionalproperties['displayName']
        mail              = $_.additionalproperties['mail']
        userPrincipalName = $_.additionalproperties['userPrincipalName']
    }
}

If you're looking for a programmatical way to flatten the object, you can start by using this example, however it's important to note that this can only handle an object which's property is nested only once, in other words, it can't handle recursion:

$newObject = [ordered]@{}
foreach($property in $object.PSObject.Properties) {
    if($property.Value -is [Collections.IDictionary]) {
        foreach($addproperty in $property.Value.GetEnumerator()) {
            $newObject[$addproperty.Key] = $addproperty.Value
        }
        continue
    }
    $newObject[$property.Name] = $property.Value
}
[pscustomobject] $newObject

The output from this would become a flattened object like this, which also, can be converted to Csv without any issue:

DeletedDateTime   : placeholder
Id                : placeholder
displayName       : placeholder
mail              : placeholder
userPrincipalName : placeholder

It's also worth noting that above example is not handling possible key collision, if there are 2 or more properties with the same name, one would override the others.

Bonus function that should work with the objects returned by the cmdlets from Graph, AzureAD and Az Modules. This function can be useful to flatten their Dictionary`2 property. It only looks one level deep if the property value implements IDictionary so don't expect it to flatten any object. For the given example should work well.

function Select-GraphObject {
    [CmdletBinding(PositionalBinding = $false)]
    param(
        [Parameter(Mandatory, ValueFromPipeline, DontShow)]
        [object] $InputObject,

        [Parameter(Position = 0)]
        [SupportsWildcards()]
        [string[]] $Properties = '*'
    )

    begin {
        $firstObject = $true
        $toSelect    = [Collections.Generic.List[object]]::new()
    }
    process {
        if($firstObject) {
            foreach($property in $InputObject.PSObject.Properties) {
                foreach($item in $Properties) {
                    if($property.Value -is [Collections.IDictionary]) {
                        foreach($key in $property.Value.PSBase.Keys) {
                            if($key -like $item -and $key -notin $toSelect.Name) {
                                $toSelect.Add(@{
                                    $key = { $_.($property.Name)[$key] }
                                })
                            }
                        }
                        continue
                    }

                    if($property.Name -like $item -and $property.Name -notin $toSelect) {
                        $toSelect.Add($property.Name)
                    }
                }
            }
            $firstObject = $false
        }

        $out = [ordered]@{}
        foreach($item in $toSelect) {
            if($item -isnot [hashtable]) {
                $out[$item] = $InputObject.$item
                continue
            }
            $enum = $item.GetEnumerator()
            if($enum.MoveNext()) {
                $out[$enum.Current.Key] = $InputObject | & $enum.Current.Value
            }
        }
        [pscustomobject] $out
    }
}

Using copies of the $object from above examples, if using the default value of -Properties, the example objects would be flattened:

PS /> $object, $object, $object | Select-GraphObject

DeletedDateTime Id          displayName mail        userPrincipalName
--------------- --          ----------- ----        -----------------
placeholder     placeholder placeholder placeholder placeholder
placeholder     placeholder placeholder placeholder placeholder
placeholder     placeholder placeholder placeholder placeholder

Or we can filter for specific properties, even Keys from the AdditionalProperties Property:

PS /> $object, $object, $object | Select-GraphObject Id, disp*, user*

Id          displayName userPrincipalName
--          ----------- -----------------
placeholder placeholder placeholder
placeholder placeholder placeholder
placeholder placeholder placeholder