Using Powershell pipe to add dynamic property to a collection of objects by calling function

Question

I have a collection of objects, each one with one property called as ProductName. I also defined a function to get parts for a product:

function GetParts([string] ProductName))
{
   $parts = @()
   ....
   return $parts
}

What I need is to use pipe to loop each object and add "Parts" as another property to the object by calling my function, and finally output the collection to a table view:

$products | Sort-Object ProductName | Select-Object `
  -Property ProductName, `
            @{Expression=(GetParts $_.ProductName); Label="Parts"} | `
          Format-Table ProductName, Parts

I put a break point in my function, but I don't get debug stop. Not sure how to use pipe for a collection with my function to add a dynamic property (Parts).

So it looks like you want the function to output an object with 2 properties, the first being a string ProductName, and the second being an array of strings Parts. Is that right? Or do you want it to output an array of objects that have 2 properties, one being a string for the ProductName and then each individual part that makes up the collection of Parts? — TheMadTechnician
– TheMadTechnician, Commented Mar 25, 2014 at 21:58
Two properties: ProductName and Parts (an array of strings). Is there any way to use pipe to call my function to output information I need? — Francis Padron
– Francis Padron, Commented Mar 25, 2014 at 22:05
I believe the expression in a calculate property needs to be wrapped in braces {} , not parens (). — mjolinor
– mjolinor, Commented Mar 25, 2014 at 22:17
For adding a property you'll need to use Add-Member, see: technet.microsoft.com/en-us/library/ff730946.aspx — oɔɯǝɹ
– oɔɯǝɹ, Commented Mar 25, 2014 at 22:23

Ansgar Wiechers · Accepted Answer · 2014-03-25 22:39:17Z

3

The expression in your calculated property must be in curly brackets, not parentheses. Change this:

Select-Object -Property ProductName, `
    @{Expression=(GetParts $_.ProductName); Label="Parts"}

into this:

select ProductName, @{Label='Parts';Expression={GetParts $_.ProductName}}

answered Mar 25, 2014 at 22:39

Ansgar Wiechers

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Comments

TheMadTechnician · Accepted Answer · 2014-03-25 22:22:05Z

2

To get it to accept values from the pipe use the parameter option ValueFromPipeline like this:

function GetParts{
    Param(
        [parameter(ValueFromPipeline = $true)]
        [string]$ProductName
    )
    Process{
       $parts = @()
       ....
       return New-Object PSObject -Property @{ProductName=$ProductName;Parts=$parts}
    }
}

That will return an object with the desired properties, and accept values from the pipe.

answered Mar 25, 2014 at 22:22

TheMadTechnician

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2 Comments

oɔɯǝɹ Over a year ago

Why do you use New-Object when you can just use Add-Member to add a new property to an existing object?

TheMadTechnician Over a year ago

@oɔɯǝɹ Because he is inputting a string, so if I just added a property it wouldn't output an object with two properties it would output a string containing the input, and a property on that string object with the array of parts. In short, it didn't give him the output he desired.

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