How to set the default output of a PowerShell class

问题

I am trying to create a PowerShell [DataTable] class derived from the standard [Data.DataTable] class to ease the creation of data tables:
_{(see also: #11987 Accelerated [DataTable] with easy constructor and AddRow method)}

class DataTable : Data.DataTable {
    [ValidateNotNullOrEmpty()][Data.DataTable]$DataTable
    DataTable([Array]$ColumnNames) {
        $This.DataTable = New-Object Data.DataTable
        ForEach ($ColumnName in $ColumnNames) {
            If ($ColumnName -is [System.Collections.IDictionary]) {
                ForEach($Key in $ColumnName.Get_keys()) { $This.AddColumn($Key, $ColumnName[$Key]) }
            } Else { $This.AddColumn($ColumnName) }
        }
    }
    [Void]AddColumn([String]$ColumnName) {
        $DataColumn = New-Object Data.DataColumn($ColumnName)
        $This.DataTable.Columns.Add($DataColumn)
    }
    [Void]AddColumn([String]$ColumnName, [Type]$ColumnType = [String]) {
        $DataColumn = New-Object Data.DataColumn($ColumnName, $ColumnType)
        $This.DataTable.Columns.Add($DataColumn)
    }
    [Void]AddRow([Array]$Array) {
        $DataRow = $This.DataTable.NewRow()
        For ($i = 0; $i -lt $Array.Length; $i++) { $DataRow.Item($i) = $Array[$i] }
        $This.DataTable.Rows.Add($DataRow)
    }
    [Void]AddRow([System.Collections.IDictionary]$Dictionary) {
        $DataRow = $This.DataTable.NewRow()
        ForEach ($Name in $Dictionary.get_Keys()) { $DataRow.Item($Name) = $Dictionary[$Name] }
        $This.DataTable.Rows.Add($DataRow)
    }
}

It works for creating new data table:

$MyDataTable = [DataTable]('a', 'b', 'c')
$MyDataTable.AddRow(@(1,2,3))

But to get the $DataTable in need to do:

$MyDataTable.DataTable
a b c
- - -
1 2 3

I want it to output the data table by default $MyDataTable.DataTable and do things like this:

$MyDataTable | ForEach-Object { ...

How can I let my class the return $This.DataTable by default?
(or is this simply not possible with a PowerShell class?)

---

Update
There were some (unrelated to the question) errors in the class which I have fixed below together with the answer from @Adam Luniewski.

class DataTable : Data.DataTable {

    DataTable([Array]$ColumnNames) {
        ForEach ($ColumnName in $ColumnNames) { $This.AddColumn($ColumnName) }
    }
    DataTable([System.Collections.IDictionary]$ColumnNameTypes) {
        ForEach($Key in $ColumnNameTypes.Get_keys()) { $This.AddColumn($Key, $ColumnNameTypes[$Key]) }
    }
    [Void]AddColumn([String]$ColumnName) {
        $DataColumn = New-Object Data.DataColumn($ColumnName)
        $This.Columns.Add($DataColumn)
    }
    [Void]AddColumn([String]$ColumnName, [Type]$ColumnType = [String]) {
        $DataColumn = New-Object Data.DataColumn($ColumnName, $ColumnType)
        $This.Columns.Add($DataColumn)
    }
    [Void]AddRow([Array]$Array) {
        $DataRow = $This.NewRow()
        For ($i = 0; $i -lt $Array.Length; $i++) { $DataRow.Item($i) = $Array[$i] }
        $This.Rows.Add($DataRow)
    }
    [Void]AddRow([System.Collections.IDictionary]$Dictionary) {
        $DataRow = $This.NewRow()
        ForEach ($Name in $Dictionary.get_Keys()) { $DataRow.Item($Name) = $Dictionary[$Name] }
        $This.Rows.Add($DataRow)
    }
}

回答1:

Your new class is extending DataTable, so it already IS DataTable. You don't need inner DataTable and can perform all the operations on $This instead of $This.DataTable. I only changed the name of the class to MyDataTable and removed inner DataTable:

class MyDataTable : Data.DataTable {

  MyDataTable([Array]$ColumnNames) {
      ForEach ($ColumnName in $ColumnNames) {
          If ($ColumnName -is [System.Collections.IDictionary]) {
              ForEach($Key in $ColumnName.Get_keys()) { $This.AddColumn($Key, $ColumnName[$Key]) }
          } Else { $This.AddColumn($ColumnName) }
      }
  }
  [Void]AddColumn([String]$ColumnName) {
      $DataColumn = New-Object Data.DataColumn($ColumnName)
      $This.Columns.Add($DataColumn)
  }
  [Void]AddColumn([String]$ColumnName, [Type]$ColumnType = [String]) {
      $DataColumn = New-Object Data.DataColumn($ColumnName, $ColumnType)
      $This.Columns.Add($DataColumn)
  }
  [Void]AddRow([Array]$Array) {
      $DataRow = $This.NewRow()
      For ($i = 0; $i -lt $Array.Length; $i++) { $DataRow.Item($i) = $Array[$i] }
      $This.Rows.Add($DataRow)
  }
  [Void]AddRow([System.Collections.IDictionary]$Dictionary) {
      $DataRow = $This.NewRow()
      ForEach ($Name in $Dictionary.get_Keys()) { $DataRow.Item($Name) = $Dictionary[$Name] }
      $This.Rows.Add($DataRow)
  }
}

$MyDataTable = [MyDataTable]('a', 'b', 'c')
$MyDataTable.AddRow(@(1,2,3))

$MyDataTable #works now:


a b c
- - -
1 2 3

来源：https://stackoverflow.com/questions/60487695/how-to-set-the-default-output-of-a-powershell-class