powershell - 缓冲管道输入到 PowerShell cmdlet 的设计模式

Question

我偶尔会遇到支持管道输入到 Cmdlet 的情况，但我希望执行的操作(例如数据库访问)对合理数量的对象进行批处理是有意义的。

实现这一目标的典型方法如下所示:

function BufferExample {
<#
.SYNOPSIS
Example of filling and using an intermediate buffer.
#>
[CmdletBinding()]
param(
    [Parameter(ValueFromPipeline)]
    $InputObject
)

BEGIN {
    $Buffer = New-Object System.Collections.ArrayList(10)
    function _PROCESS {
        # Do something with a batch of items here.
        Write-Output "Element 1 of the batch is $($Buffer[1])"
        # This could be a high latency operation such as a DB call where we 
        # retrieve a set of rows by primary key rather than each one individually.

        # Then empty the buffer.
        $Buffer.Clear()
    }
}

PROCESS {
    # Accumulate the buffer or process it if the buffer is full.
    if ($Buffer.Count -ne $Buffer.Capacity) {    
        [void]$Buffer.Add($InputObject)        
    } else {
        _PROCESS 
    }
}

END {
     # The buffer may be partially filled, so let's do something with the remainder.
    _PROCESS
}
}

有没有更少的“样板”方法来做到这一点？

一种方法可能是编写我在此处称为“_PROCESS”的函数以接受数组参数但不接受管道输入，然后将向用户公开的 cmdlet 作为代理函数构建以缓冲输入并传递缓冲区如中所述
Proxy commands .

或者，我可以在我希望编写的 cmdlet 主体中添加动态源代码以支持此功能，但这似乎容易出错并且可能难以调试/理解。

Answer 1

我从您的示例中制作了一个可重复使用的 cmdlet。

function Buffer-Pipeline {
[CmdletBinding()]
param(
    $Size = 10,
    [Parameter(ValueFromPipeline)]
    $InputObject
)
    BEGIN {
        $Buffer = New-Object System.Collections.ArrayList($Size)
    }

    PROCESS {
        [void]$Buffer.Add($_)

        if ($Buffer.Count -eq $Size) {    
            $b = $Buffer;
            $Buffer = New-Object System.Collections.ArrayList($Size)
            Write-Output -NoEnumerate $b
        }
    }

    END {
     # The buffer may be partially filled, so let's do something with the remainder.
        if ($Buffer.Count -ne 0) {  
            Write-Output -NoEnumerate $Buffer
        }
    }
}

用法:

@(1;2;3;4;5) | Buffer-Pipeline -Size 3 | % { "$($_.Count) items: ($($_ -join ','))" }

输出:

3 items: (1,2,3)
2 items: (4,5)

另一个例子:

1,2,3,4,5 | Buffer-Pipeline -Size 10 | Measure-Object

Count    : 2

处理每批:

 1,2,3 | Buffer-Pipeline -Size 2 | % { 
    $_ | % { "Starting batch of $($_.Count)" } { $_ * 100 } { "Done with batch of $($_.Count)" }
}

Starting batch of 2
100
200
Done with batch of 2
Starting batch of 1
300
Done with batch of 1