Prevent powershell select-object from turning single item array of object in to object

Question

I am querying the ResourceRecordSets in an AWS Route53 zone. I am trying to transform the name of the properties with select-object.

There are two records in the records sets. One has two items in the ResourceRecords the other has one item in ResourceRecords.

PS> (Get-R53ResourceRecordSet -HostedZoneId $zone.Id -MaxItem 1000).ResourceRecordSets

Name                    : simple.my-domain.com.
Type                    : A
SetIdentifier           : 
Weight                  : 0
Region                  : 
GeoLocation             : 
Failover                : 
MultiValueAnswer        : False
TTL                     : 300
ResourceRecords         : {Amazon.Route53.Model.ResourceRecord, Amazon.Route53.Model.ResourceRecord}
AliasTarget             : 
HealthCheckId           : 
TrafficPolicyInstanceId : 
CidrRoutingConfig       : 
GeoProximityLocation    : 

Name                    : weighted.my-domain.com.
Type                    : A
SetIdentifier           : my record id
Weight                  : 0
Region                  : 
GeoLocation             : 
Failover                : 
MultiValueAnswer        : False
TTL                     : 300
ResourceRecords         : {Amazon.Route53.Model.ResourceRecord}
AliasTarget             : 
HealthCheckId           : 
TrafficPolicyInstanceId : 
CidrRoutingConfig       : 
GeoProximityLocation    :

Each Amazon.Route53.Model.ResourceRecord is an object with a single property named Value.

PS> (Get-R53ResourceRecordSet -HostedZoneId $zone.Id -MaxItem 1000).ResourceRecordSets[0].ResourceRecords | Get-Member

   TypeName: Amazon.Route53.Model.ResourceRecord

Name        MemberType Definition
----        ---------- ----------
Equals      Method     bool Equals(System.Object obj)
GetHashCode Method     int GetHashCode()
GetType     Method     type GetType()
ToString    Method     string ToString()
Value       Property   string Value {get;set;}

I want to rename ResourceRecords to resource_records and Value to value. To simplify and troubleshoot I am trying just to convert ResourceRecords to resource_records

PS> (Get-R53ResourceRecordSet -HostedZoneId $zone.Id -MaxItem 1000).ResourceRecordSets | Select-Object Name, Type, Weight, MultiValueAnswer, @{N='resource_records';E={$_.ResourceRecords}}

Name             : simple.my-domain.com.
Type             : A
Weight           : 0
MultiValueAnswer : False
resource_records : {Amazon.Route53.Model.ResourceRecord, Amazon.Route53.Model.ResourceRecord}

Name             : weighted.my-domain.com.
Type             : A
Weight           : 0
MultiValueAnswer : False
resource_records : Amazon.Route53.Model.ResourceRecord

But, it seems to convert the single item object array into an object. {Amazon.Route53.Model.ResourceRecord} has become Amazon.Route53.Model.ResourceRecord.

I have tried numerous ideas to try to prevent this from happening, and if it doesn't flat out fail it still always produces the same output.

For instance, I have tried casting it to an array:

PS> (Get-R53ResourceRecordSet -HostedZoneId $zone.Id -MaxItem 1000).ResourceRecordSets | Select-Object Name, Type, Weight, MultiValueAnswer, @{N='resource_records';E={@($_.ResourceRecords)}}

But, this doesn't make any difference.

Is there any way to prevent this from being converted into a non-array?

mklement0 · Accepted Answer · 2024-04-02 04:10:21Z

2

Given that you know $_.ResourceRecords to be an array, use the unary form of the array-construction operator , to wrap it in an an aux., transitory single-element array, so as to ultimately output it as-is.

Here's a simplified example:

@(
  [pscustomobject] @{ ResourceRecords = @(1) }
  [pscustomobject] @{ ResourceRecords = @(2, 3) }
) | 
  Select-Object @{ N='resource_records'; E={ , $_.ResourceRecords } }

The conceptually clearer, but more verbose and slower alternative is to use
Write-Output -NoEnumerate $_.ResourceRecords in lieu of , $_.ResourceRecords

This is necessary, because the output from a script block ({ ... }) assigned to the Expression (E) entry of a hashtable defining a calculated property exhibits pipeline logic:

That is, outputting an array causes it to be auto-enumerated, i.e. its elements are output, one by one, and if there happens to be just one element, that element is collected as-is; only two or more elements are captured in an array (of type [object[]], irrespective of the type of the source array).
The techniques above prevent this enumeration and ensure that the source array is preserved as-is as the value of the calculated property.

edited Apr 2, 2024 at 4:10

answered Apr 2, 2024 at 3:58

mklement0

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3 Comments

Appleoddity Over a year ago

This absolutely works. I'm still plugging away and expanding this to @{N='resource_records';E={, ($_.ResourceRecords | Select-Object @{N="value";E={$_.Value}})}} - that was one variation of attempts so far. Once I add the renaming of the value property I run in to the same problem.

Appleoddity Over a year ago

Whew. Finally cracked it. Thanks for your help. @{N='resource_records';E={, @($_.ResourceRecords | foreach-object { @{"value" = $_.Value.Trim("`"")}})}}

mklement0 Over a year ago

Only just saw this now, @Appleoddity. I'm glad the answer helped and that you worked out the rest yourself.

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