Passing Ordered hash table to a script block breaks the order

Question

I'm trying to collect some info from remote hosts in form of a CSV string. I need the values to be returned in particular order to accumulate them in one CSV file.

I use ordered hash table to keep keys in particular order, but when I pass it to a remote host the order gets broken.

Is there a way to preserve the order?

$ordered_hash = [ordered]@{"a" = 1; "b" = 2; "c" = 3}
$ordered_hash
$scriptblock = {
param ($hash)
$hash
} 
Invoke-Command -ComputerName localhost -ScriptBlock $scriptblock -ArgumentList ([hashtable]$ordered_hash)

Returns:

Name                           Value                                                                                                                                     
----                           -----                                                                                                                                     
a                              1                                                                                                                                         
b                              2                                                                                                                                         
c                              3                                                                                                                                         
c                              3                                                                                                                                         
b                              2                                                                                                                                         
a                              1

A possible workaround: https://stackoverflow.com/q/14891044/56778 — Jim Mischel, Dec 16 '17 at 23:11
`-ArgumentList ([hashtable]$ordered_hash)` -> `-ArgumentList $ordered_hash`? — Ansgar Wiechers, Dec 16 '17 at 23:16
It is know issue with PowerShell serialization system: `$s = [System.Management.Automation.PSSerializer]; $o = [ordered]@{}; $o.GetType().FullName; $s::Deserialize($s::Serialize($o)).GetType().FullName` — user4003407, Dec 17 '17 at 04:22
I tried to pass an argument without [hashtable] definition, but that made no difference, The order got lost . — Papa Smurf, Dec 18 '17 at 05:11
@PapaSmurf If you want to notify someone of your comment, then you should use `@UserName` syntax. — user4003407, Dec 18 '17 at 18:48

score 2 · Answer 1 · answered Dec 16 '17 at 23:18

2

When you define a hash table using [ordered] attribute, in fact it creates a System.Collections.Specialized.OrderedDictionary.

When passing it to a parameter of HashTable type, it converts the OrderedDictionary to HashTable which is no more ordered.

To keep the order, you can use either of following options:

Remove the type from parameters of the script block to prevent a type change. This way it will use the original type which is use OrderedDictionary.

Or

Use System.Collections.Specialized.OrderedDictionary type of the parameter of the script block.

answered Dec 16 '17 at 23:18

Reza Aghaei

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I tried both options with the example which you shared and both of them work properly. Let me know if you have any question about the answer ... – Reza Aghaei Dec 18 '17 at 06:09
Didn't work for me. I got the same result. $ordered_hash = [ordered]@{"a" = 1; "b" = 2; "c" = 3} $ordered_hash $scriptblock = { param ($hash) $hash } Invoke-Command -ComputerName localhost -ScriptBlock $scriptblock -ArgumentList ([System.Collections.Specialized.OrderedDictionary]$ordered_hash) – Papa Smurf Dec 18 '17 at 11:58

Passing Ordered hash table to a script block breaks the order

1 Answers1