Powershell missing array after conversion hashtable to json

Question

Working with Graph API and Intune. I create hash table in my script and covert it to JSON which POST to GraphAPI. But in one case during conversion I lose array. Because of this GraphAPI does not want to accept JSON and returns error.

Case when conversion is correct:

$TargetGroupIDs = @('111', '222')
$AppAssignment = @{
  mobileAppAssignments = @{
  }
}

$AppAssignment.mobileAppAssignments = foreach ($GroupID in $TargetGroupIDs) {
  $Hash = [ordered]@{
    "@odata.type" = "#microsoft.graph.mobileAppAssignment"
    intent        = "Required"
    settings      = $null
    target        = @{
      "@odata.type" = "#microsoft.graph.groupAssignmentTarget"
      groupId       = "$GroupID"
    }
  }
  write-output (New-Object -Typename PSObject -Property $hash)
}

$AppAssignment | ConvertTo-Json -Depth 50

Output:

{
  "mobileAppAssignments": [
    {
      "@odata.type": "#microsoft.graph.mobileAppAssignment",
      "intent": "Required",
      "settings": null,
      "target": {
        "groupId": "111",
        "@odata.type": "#microsoft.graph.groupAssignmentTarget"
      }
    },
    {
      "@odata.type": "#microsoft.graph.mobileAppAssignment",
      "intent": "Required",
      "settings": null,
      "target": {
        "groupId": "222",
        "@odata.type": "#microsoft.graph.groupAssignmentTarget"
      }
    }
  ]
}

But when I have one element in $TargetGroupIDs conversion is not correct:

$TargetGroupIDs = @('111')
$AppAssignment = @{
  mobileAppAssignments = @{
  }
}

$AppAssignment.mobileAppAssignments = foreach ($GroupID in $TargetGroupIDs) {
  $Hash = [ordered]@{
    "@odata.type" = "#microsoft.graph.mobileAppAssignment"
    intent        = "Required"
    settings      = $null
    target        = @{
      "@odata.type" = "#microsoft.graph.groupAssignmentTarget"
      groupId       = "$GroupID"
    }
  }
  write-output (New-Object -Typename PSObject -Property $hash)
}

$AppAssignment | ConvertTo-Json -Depth 50

Output:

{
  "mobileAppAssignments": {
    "@odata.type": "#microsoft.graph.mobileAppAssignment",
    "intent": "Required",
    "settings": null,
    "target": {
      "groupId": "111",
      "@odata.type": "#microsoft.graph.groupAssignmentTarget"
    }
  }
}

Please note difference in brackets after mobileAppAssignments. In first case [], but in second case {}.

Could someone tell what I am missing in second case?

Surround your `foreach` loop with the array subexpression operator: `$AppAssignment.mobileAppAssignments = @(foreach ($GroupID in $TargetGroupIDs) { ... })` — Theo, May 23 '22 at 14:39
Alternatively replace `foreach` by the `.ForEach` intrinsic method, which always outputs an array-like collection: `$AppAssignment.mobileAppAssignments = $TargetGroupIDs.ForEach{` and replace `$GroupID` by `$_`. — zett42, May 23 '22 at 15:49

mklement0 · Accepted Answer · 2022-05-24T12:41:00.880

Theo and Santiago Squarzon have provided the crucial hint in the comments, but let me spell it out:

To ensure that the output from your foreach statement is an array, enclose it in @(), the array-subexpression operator:

$AppAssignment.mobileAppAssignments = @(
  foreach ($GroupID in $TargetGroupIDs) {
    [pscustomobject] @{
      "@odata.type" = "#microsoft.graph.mobileAppAssignment"
      intent        = "Required"
      settings      = $null
      target        = @{
        "@odata.type" = "#microsoft.graph.groupAssignmentTarget"
        groupId       = "$GroupID"
      }
    }
  }
)

^{Also note that simplified syntax custom-object literal syntax ([pscustomobject] @{ ... }).}

@(...) ensures that an array (of type [object[]]) is returned, irrespective of how many objects, if any, the foreach statement outputs.

Without @(...), the data type of the collected output depends on the number of output objects produced by a statement or command:

If there is no output object, the special "AutomationNull" value is returned, which signifies the absence of output; this special value behaves like an empty collection in enumeration contexts, notably the pipeline, and like $null in expression contexts - see this answer for more information; in the context at hand, it would be converted to a null JSON value.
If there is one output object, it is collected as-is, as itself - this is what you saw.
Only with two or more output objects do you get an array (of type [object[]]).

Note: The behavior above follows from the streaming behavior of the PowerShell pipeline / its success output stream: object are emitted one by one, and needing to deal with multiple objects only comes into play if there's a need to collect output objects: see this answer for more information.

Thank for detailed response. I not only resolved my problem, but also understood root cause. — Vindi4i, May 24 '22 at 08:49

Powershell missing array after conversion hashtable to json

1 Answers1