PowerShell函数将不会返回DataTable [英] PowerShell function will not return DataTable

问题描述

我在PowerShell v4.0（Windows 7 x64 SP1）上有一个PowerShell脚本，该脚本创建了一个非常复杂的DataTable。我希望能够轻松地将DataTable代码放置在任何地方，因此我决定将其包装在一个简单的函数中，例如：

I've got a PowerShell script on PowerShell v4.0 (Windows 7 x64 SP1) that creates a pretty complex DataTable. I wanted to be able to place that DataTable code anywhere pretty easily, so I decided to wrap it in a simple function, like so:

function Get-UserDataTable
{
    $DataTable = New-Object -TypeName System.Data.DataTable -ArgumentList 'User';

    $NewColumn = $DataTable.Columns.Add('Id',[System.Int32]);
    $NewColumn.AllowDBNull = $false;
    $NewColumn.Unique = $true;

    $NewColumn = $DataTable.Columns.Add('FirstName',[System.String]);
    $NewColumn.MaxLength = 64;

    $NewColumn = $DataTable.Columns.Add('MiddleName',[System.String]);
    $NewColumn.MaxLength = 64;

    $NewColumn = $DataTable.Columns.Add('LastName',[System.String]);
    $NewColumn.MaxLength = 64;

    return $DataTable;
}

但是，该代码始终返回空对象。我尝试了写入输出$ DataTable ，返回$ DataTable.Copy（）和 $ DataTable ，但该功能始终始终为空。

However, that code always returns a null object. I tried Write-Output $DataTable, return $DataTable.Copy(), and $DataTable, but the function is still always null.

因此，我想我可以尝试添加一些行。我总是可以清除DataTable，但仍然可以减少这种编码：

So, I thought I might try adding some rows. I can always clear the DataTable, and it'd still be less coding this way:

function Get-UserDataTable2
{
    $DataTable = New-Object -TypeName System.Data.DataTable -ArgumentList 'User';

    $NewColumn = $DataTable.Columns.Add('Id',[System.Int32]);
    $NewColumn.AllowDBNull = $false;
    $NewColumn.Unique = $true;

    $NewColumn = $DataTable.Columns.Add('FirstName',[System.String]);
    $NewColumn.MaxLength = 64;

    $NewColumn = $DataTable.Columns.Add('MiddleName',[System.String]);
    $NewColumn.MaxLength = 64;

    $NewColumn = $DataTable.Columns.Add('LastName',[System.String]);
    $NewColumn.MaxLength = 64;

    $NewRow = $DataTable.NewRow();
    $NewRow.Id = 1;
    $NewRow.FirstName = 'Test';
    $NewRow.MiddleName = '';
    $NewRow.LastName = 'User';

    $DataTable.Rows.Add($NewRow);

    $NewRow = $DataTable.NewRow();
    $NewRow.Id = 2;
    $NewRow.FirstName = 'Other';
    $NewRow.MiddleName = 'Test';
    $NewRow.LastName = 'User';

    $DataTable.Rows.Add($NewRow);

    return $DataTable;
}

不是。此函数返回一个 [System.Object []] ，其中包含单个 [System.Data.DataRow] 。一个数据行的对象数组。

Nope. This function returns a [System.Object[]] containing individual [System.Data.DataRow]. An object array of DataRows.

如何从PowerShell中的函数返回数据表？

How can I return a DataTable from a function in PowerShell?

推荐答案

正如PerSerAl的注释中的链接所暗示的，该问题是由于DataTable不是可枚举的数据类型引起的。为了使它可枚举，可以使用一元逗号运算符将其作为单个元素放入数组中。数组是可枚举的。

As the link in PerSerAl's comment suggests, the issue is caused because DataTable isn't an enumerable data type. To force it to be enumerable, you can use the unary comma operator to put it into an array as a single element. Arrays are enumerable.

function Get-UserDataTable
{
    $DataTable = New-Object -TypeName System.Data.DataTable -ArgumentList 'User';

    $NewColumn = $DataTable.Columns.Add('Id',[System.Int32]);
    $NewColumn.AllowDBNull = $false;
    $NewColumn.Unique = $true;

    $NewColumn = $DataTable.Columns.Add('FirstName',[System.String]);
    $NewColumn.MaxLength = 64;

    $NewColumn = $DataTable.Columns.Add('MiddleName',[System.String]);
    $NewColumn.MaxLength = 64;

    $NewColumn = $DataTable.Columns.Add('LastName',[System.String]);
    $NewColumn.MaxLength = 64;

    return ,$DataTable;
}

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