Detect an array of empty objects

Question

I'm calling the VSTS Pull Request Query documented here: https://learn.microsoft.com/en-us/rest/api/vsts/git/pull%20request%20query/get?view=vsts-rest-4.1

It returns an object array of results. I wanted to detect when no results are returned and react accordingly. I thought I could check the response.results.length, but it will be 1 even if there are no results. It returns an array of 1 empty object. I'm having a hard time detecting that condition. The one solution I thought of is:

    if(($pullRequests.results | Get-Member -MemberType Properties).Length -eq 0){some code}

Since a vanilla ps object has 4 members and the populated object has an additional note property it will work. My method seems hackish, is there a better approach?

I tried checking length, exists, and bool:

    PS> $pullRequests.results[0].Length
    1
    PS> $temp = $pullRequests.results[0]
    PS> $temp | Get-Member

    TypeName: System.Management.Automation.PSCustomObject

    Name        MemberType Definition
    ----        ---------- ----------
    Equals      Method     bool Equals(System.Object obj)
    GetHashCode Method     int GetHashCode()
    GetType     Method     type GetType()
    ToString    Method     string ToString()

    PS> $temp -eq $null
    False
    PS> if($temp){"YAY"}else{"BOO"}
    YAY

That actually sounds like a bug in the API -- an empty array is not an empty object. How are you getting $pullRequests -- with Invoke-RestMethod? Try Invoke-WebRequest to see what it's actually returning and whether that can be massaged before passing it to ConvertFrom-Json. (That also suggest the reverse should be possible -- checking for ($pullRequests.results[0] | ConvertTo-Json -Compress) -eq "{}". Though that's still a bit hackish and inefficient.) — Jeroen Mostert
– Jeroen Mostert, Commented Aug 22, 2018 at 13:29
If I use webRequest the response content contains: "results":[{}] — JDH
– JDH, Commented Aug 22, 2018 at 13:35
Then I would check if the response you're getting is [{}] and | ConvertFrom-Json otherwise. — Ansgar Wiechers
– Ansgar Wiechers, Commented Aug 22, 2018 at 13:41
Per the docs, "each entry in the list is a dictionary of commit->pull requests." So technically, if you supply it one query it's correct to return one empty dictionary. If multiple queries were supplied, each of these could be empty. To see if an individual result is not empty, the cleanest way is probably if ($result | Get-Member -Type Properties). — Jeroen Mostert
– Jeroen Mostert, Commented Aug 22, 2018 at 13:47

Bruce Payette · Accepted Answer · 2018-08-22 16:19:46Z

1

This does sound like a bug in the API. As a work around, checking for properties (as opposed to members which also includes methods) seems like the right approach. The easiest way to do this ix as follows:

if ($pullRequests.PSObject.Properties)
{
    "Object has properties so process it."
}
else
{
    "Object has no properties, ignore it."
}

answered Aug 22, 2018 at 16:19

Bruce Payette

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3 Comments

JDH Over a year ago

Looks like this object has some default properties on it: PS>$pullRequests.results.PSObject.Properties | select name Name ---- Count Length LongLength Rank SyncRoot IsReadOnly IsFixedSize IsSynchronized

iRon Over a year ago

Reading the question, I think is should be $pullRequests.results[0].PSObject.Properties or $Temp.PSObject.Properties. The problem with this solution could be that if there is no .results at all, you will get a Cannot index into a null array error.

JDH Over a year ago

This is probably the closest to the answer I've settled on. I had to wrap the properties in an array: if (@($pullRequests.results[0].PSObject.Properties).Count -eq 0) {}

Adam · Accepted Answer · 2018-08-22 14:54:19Z

0

Oh man, that stinks.

Lemme make sure I understand your problem. You're expecting an object that looks something like the following when data is returned:

$full_collection_ps_objects = `
    @([PSCustomObject]@{a=1;b=2}, [PSCustomObject]@{a=1;b=3})

A collection of psobjects.

When no data is returned, you get an array of objects with a single empty psobject:

$empty_collection_ps_objects = @([PSCustomObject]@{})

I think you nailed it. Property count is a good indicator. I'm a little neurotic. That might lead me to get paranoid that another default property might appear at some later point. I might consider looking for specific field name, a primary key of sorts with something like:

if( $($empty_collection_ps_objects | Get-Member).Name -contains 'a' ) { $true }
if( $($full_collection_ps_objects | Get-Member).Name -contains 'a' ) { $true }

answered Aug 22, 2018 at 14:54

Adam

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5 Comments

JDH Over a year ago

One challenge with this approach. The property that comes back is a guid which I won't know ahead of time.

Adam Over a year ago

The guid is the value or the column? You're getting the commit hash from VSTS. I would've thought that the commit hash would come back in a field named "commit" or something like that.

JDH Over a year ago

The column. Running this: "($pullRequests.results | get-member).Name" returns you: "Equals GetHashCode GetType ToString x7f98xxx40d5exxx0f4xxxe04xxx8c8xxxe19xxx"

JDH Over a year ago

I added some x's since we're a little crazy about any kind of indentifying data :)

Adam Over a year ago

Gotcha. No, I see your point then. This won't work for your use-case. I assumed the column names were static and known.

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