Background

Playing around with Powershell and ran into an error that one should avoid through defensive programming.

Error

Error – Image

Error – Text

The property 'nationality' cannot be found on this object. Verify that the property exists.
At property\customObject.property.ps1:57 char:33
+         Write-Host "`tNationality: '$($person.nationality)'";
+                                       ~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : NotSpecified: (:) [], PropertyNotFoundException
    + FullyQualifiedErrorId : PropertyNotFoundStrict

        Nationality: ''

Outline

1. We will create a few standalone objects using PSCustomObject
2. Add created objects into an array
3. Iterate through the array
4. Access each object
   • Retrieve property
5. Because our object’s properties are created on the fly, there is no inherent type checking
6. On our last object, we will intentionally skip setting the nationality property

Code

Set-StrictMode -Version 2.0

# initialize the array
[PsObject[]]$objCandidate = @()

$objHuman1 = [pscustomobject]@{
    name='L.L. Cool J';
    gender='M';
    nationality='American';
}

$objHuman2 = [pscustomobject]@{
    name='Fresh Prince';
    gender='M';
    nationality='American';

}

$objHuman3 = [pscustomobject]@{
    name='Slick Rick';
    gender='M';
}

$objCandidate += $objHuman1;
$objCandidate += $objHuman2;
$objCandidate += $objHuman3;

foreach($person in $objCandidate) {

    Write-Host "`tName:- '$($person.Name)'";

    Write-Host "`tGender:- '$($person.gender)'";

    Write-Host "`tNationality: '$($person.nationality)'";

    Write-Host "";

}

Workaround

Outline

1. Get a list of the object’s properties name
2. Perform an “in” search against the list

Code

[string] $propertyNationality = 'nationality';

function hasProperty($object, $propertyName)
{
    $hasProperty = $propertyName -in $object.PSobject.Properties.Name;

    return($hasProperty);
}

foreach($person in $objCandidate) {

    # Does object have property
    $propNationalityExists = hasProperty $person $propertyNationality;

    Write-Host "`tName:- '$($person.Name)'";

    Write-Host "`tGender:- '$($person.gender)'";

    if ( ($propNationalityExists -eq $True)
    {

        Write-Host "`tNationality: '$($person.nationality)'";
    }

    Write-Host "";

}

Crediting

dan-gph

Link

Code Sharing

GitHub

Repository

DanielAdeniji/powershell.customObject

Folder

Link

Files

1. property.dadeniji.noValidation.ps1
   Link
2. property.dadeniji.validation.ps1
   Link

References

1. Stack Overflow
   • How can you test if an object has a specific property
     Link
   • How to dynamically add new properties to custom object in PowerShell
     Link
   • How to initialize an array of custom objects
     Link