Custom objects default display in PowerShell 3.0

In PowerShell 3.0 we can now create new custom objects using a hash table.

PS> [PSCustomObject]@{
   One = 1 
   Two = 2 
   Three = 3 
   Four = 4 
   Five = 5 
}


One   : 1
Two   : 2
Three : 3
Four  : 4
Five  : 5 

Behind the scenes, PowerShell creates a hash table and wraps it a PSCustomObject. It is way faster than using the New-Object cmdlet and it also provides consistency, while maintaining backwards compatibility. Another benefit of using PSCustomObject over New-Object is property order. PSCustomObject preserve the order of defined properties while New-Object doesn't.

PS > [PSCustomObject]@{One=1;Two=2;Three=3} 

One Two Three
--- --- -----
  1   2     3


PS > New-Object PSObject -Property @{One=1;Two=2;Three=3}

One Three Two
--- ----- ---
  1     3   2

Notice that when the new PSCustomObject is returned, all of its properties are displayed in the console. We can control the default display property set of an object by setting a DefaultDisplayPropertySet.

$psco = [PSCustomObject]@{
   One = 1
   Two = 2
   Three = 3
   Four = 4
   Five = 5 
}

 
[string[]]$DefaultProperties = 'Two','Four','Five'

# Add the PSStandardMembers.DefaultDisplayPropertySet member
$ddps = New-Object System.Management.Automation.PSPropertySet `
         DefaultDisplayPropertySet,$DefaultProperties
$PSStandardMembers = [System.Management.Automation.PSMemberInfo[]]$ddps 

# Attach default display property set
$psco | Add-Member -MemberType MemberSet -Name PSStandardMembers `
         -Value $PSStandardMembers -PassThru



Two Four Five
--- ---- ----
  2    4    5

We can also define the properties of the type that will be displayed by default with the formatting cmdlets.

PS> Get-Date | Format-List 
PS> Update-TypeData -TypeName System.DateTime -DefaultDisplayPropertySet `
       DateTime,DayOfWeek,Year,Month,Day 
PS> Get-Date | Format-List 

DisplayHint : DateTime
Date        : 4/9/2012 12:00:00 AM
Day         : 9
DayOfWeek   : Monday
DayOfYear   : 100
Hour        : 8
Kind        : Local
Millisecond : 598
Minute      : 15
Month       : 4
Second      : 38
Ticks       : 634695561385980985
TimeOfDay   : 08:15:38.5980985
Year        : 2012
DateTime    : Monday, April 09, 2012 8:15:38 AM


DateTime  : Monday, April 09, 2012 8:15:39 AM
DayOfWeek : Monday
Year      : 2012
Month     : 4
Day       : 9

I have put together a function that wraps the process of creating a new PSCustomObject and specifying a list of default properties to display.

function New-PSCustomObject
{
       [CmdletBinding()] 

       param(
              [Parameter(Mandatory,Position=0)]
              [ValidateNotNullOrEmpty()]
              [System.Collections.Hashtable]$Property,

              [Parameter(Position=1)]
              [ValidateNotNullOrEmpty()]
              [Alias('dp')]
              [System.String[]]$DefaultProperties
       )


       $psco = [PSCustomObject]$Property 

       # define a subset of properties
       $ddps = New-Object System.Management.Automation.PSPropertySet `
                DefaultDisplayPropertySet,$DefaultProperties
       $PSStandardMembers = [System.Management.Automation.PSMemberInfo[]]$ddps 

       # Attach default display property set
       $psco | Add-Member -MemberType MemberSet -Name PSStandardMembers `
                -Value $PSStandardMembers -PassThru
}

# usage example
# define 5 properties 
PS> $property = @{Name='My Object';One=1;Two=2;Three=3;Four=4} 

# create the object and set just three properties for default display
PS> New-PSCustomObject -Property $property -DefaultProperties Name,Two,Four 

Two Four Five
--- ---- ----
  2    4    5