How to return a specific type from a function

Hello. I've written a routine that writes an XML file into a Data Table
([system.Data.DataTable]), and it performs exactly the way I want it to, but
when i put the routine inside a function and try to return the table at the
end by using "return $table", it loses the datatype of
[system.Data.DataTable]. It becomes an array. I can verify this by running
$table.gettype() before and after it exits the function. Before the return,
it says System.Data.DataRow. After the return, it says System.Array. I've
tried forcing it by saying [System.Data.Table]$table = loadtable but it
errors with the following message:
Cannot convert "System.Object[]" to "System.Data.DataTable".
You cannot call a method on a null-valued expression.

So really, my question is, in Powershell, can you tell a function to return
it's data as a specific data type? Any help would be appreciated.

Thanks!

Janssen Jones

If your return value is getting wrapped in an array, you may be returning
multiple values. I just tried creating a function that simply returned
"new-object System.Data.DataTable", and that worked as expected...calling
GetType() on the return value returned DataTable. Have you poked through the
array that's getting returned and made sure there's only one thing in it?
Due to the way Powershell manages interaction with the pipeline, it's pretty
easy to accidentally return something that you just meant to calculate and
store. Any expression that returns a value that you invoke without storing
the result ends up on the return pipeline, not just the last expression in
the function -- the return statement is actually optional. Try invoking the
function "function foo { 'bar';'baz'; }", and you'll see what I mean. Try
printing out the Length property of the return value and see what it says.
If it says 1, I'd be very interested in seeing your script...if you post it,
or a simplification of it that still shows the behaviour you're seeing if
it's long or confidential, maybe someone can figure it out. Hope this helps.

-- Ryan Milligan

"Janssen" <Janssen@discussions.microsoft.com> wrote in message
news:EB5299B2-446A-4E74-B90B-1C62844464FA@microsoft.com...
> Hello. I've written a routine that writes an XML file into a Data Table
> ([system.Data.DataTable]), and it performs exactly the way I want it to,
> but
> when i put the routine inside a function and try to return the table at
> the
> end by using "return $table", it loses the datatype of
> [system.Data.DataTable]. It becomes an array. I can verify this by
> running
> $table.gettype() before and after it exits the function. Before the
> return,
> it says System.Data.DataRow. After the return, it says System.Array.
> I've
> tried forcing it by saying [System.Data.Table]$table = loadtable but it
> errors with the following message:
> Cannot convert "System.Object[]" to "System.Data.DataTable".
> You cannot call a method on a null-valued expression.
>
> So really, my question is, in Powershell, can you tell a function to
> return
> it's data as a specific data type? Any help would be appreciated.
>
> Thanks!
>
> Janssen Jones
>

Thanks for the info. I'm trying to return 17 rows of a table completely
intact to be used as the same table outside of the function. What i notice
happening is that when it leaves the function, it still looks like everything
is there, but i no longer have access to table.rows.count. It is functioning
like an array instead of a datatable. Here's my function:
function load-table
{
[xml]$subnets = gc ~\Desktop\halls.xml
$table = New-Object system.Data.DataTable "subnets"
$col1 = New-Object system.data.DataColumn building
$col2 = New-Object system.data.DataColumn oc1, ([int])
$col3 = New-Object system.data.DataColumn oc2, ([int])
$col4 = New-Object system.data.DataColumn oc3, ([int])
$col5 = New-Object system.data.DataColumn oc4, ([int])
$col6 = New-Object system.data.DataColumn range
$table.columns.add($col1)
$table.columns.add($col2)
$table.columns.add($col3)
$table.columns.add($col4)
$table.columns.add($col5)
$table.columns.add($col6)
$i=0
$j= $subnets.subnets.subnet.length
$row = @()
while ($i -lt $j)
{
[array]$row += ""
$row[$i] = $table.newrow()
$row[$i].building = $subnets.subnets.subnet[$i].building
$row[$i].oc1 = $subnets.subnets.subnet[$i].octet1
$row[$i].oc2 = $subnets.subnets.subnet[$i].octet2
$row[$i].oc3 = $subnets.subnets.subnet[$i].octet3
$row[$i].oc4 = $subnets.subnets.subnet[$i].octet4
$row[$i].range = $subnets.subnets.subnet[$i].sub
$table.rows.add($row[$i])
$i++
}
Write-Host $table.rows.count
return $table
}

$table
$table.rows.count

$table.rows.count returns "17" inside the function, but nothing outside the
function. In fact, though all the data is still there, $table.rows no longer
exists.

I hope that makes some sense.

Thanks for your help.

Janssen



"Janssen" wrote:

> Hello. I've written a routine that writes an XML file into a Data Table
> ([system.Data.DataTable]), and it performs exactly the way I want it to, but
> when i put the routine inside a function and try to return the table at the
> end by using "return $table", it loses the datatype of
> [system.Data.DataTable]. It becomes an array. I can verify this by running
> $table.gettype() before and after it exits the function. Before the return,
> it says System.Data.DataRow. After the return, it says System.Array. I've
> tried forcing it by saying [System.Data.Table]$table = loadtable but it
> errors with the following message:
> Cannot convert "System.Object[]" to "System.Data.DataTable".
> You cannot call a method on a null-valued expression.
>
> So really, my question is, in Powershell, can you tell a function to return
> it's data as a specific data type? Any help would be appreciated.
>
> Thanks!
>
> Janssen Jones
>

Oh, I see the problem. DataTable implements IEnumerable, so PSH flattens it
and returns its contents on the pipeline instead of the collection itself.
To avoid this, simply put a comma in front of the value you want to return,
like so:

return ,$table;

This essentially creates an array that contains only $table -- PSH only
flattens one level of enumerables, so $table is passed directly on the
pipeline instead of its contents.

-- Ryan Milligan

"Janssen" <Janssen@discussions.microsoft.com> wrote in message
news:C20EF777-C515-45CB-BFB6-436C09FC8222@microsoft.com...
> Thanks for the info. I'm trying to return 17 rows of a table completely
> intact to be used as the same table outside of the function. What i
> notice
> happening is that when it leaves the function, it still looks like
> everything
> is there, but i no longer have access to table.rows.count. It is
> functioning
> like an array instead of a datatable. Here's my function:
> function load-table
> {
> [xml]$subnets = gc ~\Desktop\halls.xml
> $table = New-Object system.Data.DataTable "subnets"
> $col1 = New-Object system.data.DataColumn building
> $col2 = New-Object system.data.DataColumn oc1, ([int])
> $col3 = New-Object system.data.DataColumn oc2, ([int])
> $col4 = New-Object system.data.DataColumn oc3, ([int])
> $col5 = New-Object system.data.DataColumn oc4, ([int])
> $col6 = New-Object system.data.DataColumn range
> $table.columns.add($col1)
> $table.columns.add($col2)
> $table.columns.add($col3)
> $table.columns.add($col4)
> $table.columns.add($col5)
> $table.columns.add($col6)
> $i=0
> $j= $subnets.subnets.subnet.length
> $row = @()
> while ($i -lt $j)
> {
> [array]$row += ""
> $row[$i] = $table.newrow()
> $row[$i].building = $subnets.subnets.subnet[$i].building
> $row[$i].oc1 = $subnets.subnets.subnet[$i].octet1
> $row[$i].oc2 = $subnets.subnets.subnet[$i].octet2
> $row[$i].oc3 = $subnets.subnets.subnet[$i].octet3
> $row[$i].oc4 = $subnets.subnets.subnet[$i].octet4
> $row[$i].range = $subnets.subnets.subnet[$i].sub
> $table.rows.add($row[$i])
> $i++
> }
> Write-Host $table.rows.count
> return $table
> }
>
> $table
> $table.rows.count
>
> $table.rows.count returns "17" inside the function, but nothing outside
> the
> function. In fact, though all the data is still there, $table.rows no
> longer
> exists.
>
> I hope that makes some sense.
>
> Thanks for your help.
>
> Janssen
>
>
>
> "Janssen" wrote:
>
>> Hello. I've written a routine that writes an XML file into a Data Table
>> ([system.Data.DataTable]), and it performs exactly the way I want it to,
>> but
>> when i put the routine inside a function and try to return the table at
>> the
>> end by using "return $table", it loses the datatype of
>> [system.Data.DataTable]. It becomes an array. I can verify this by
>> running
>> $table.gettype() before and after it exits the function. Before the
>> return,
>> it says System.Data.DataRow. After the return, it says System.Array.
>> I've
>> tried forcing it by saying [System.Data.Table]$table = loadtable but it
>> errors with the following message:
>> Cannot convert "System.Object[]" to "System.Data.DataTable".
>> You cannot call a method on a null-valued expression.
>>
>> So really, my question is, in Powershell, can you tell a function to
>> return
>> it's data as a specific data type? Any help would be appreciated.
>>
>> Thanks!
>>
>> Janssen Jones
>>

Theres a similar issue in this thread that may be of interest

http://www.microsoft.com/communities...a-25ec4df4014d

--
Richard Siddaway
Please note that all scripts are supplied "as is" and with no warranty
Blog: http://richardsiddaway.spaces.live.com/
PowerShell User Group: http://www.get-psuguk.org.uk


"Ryan Milligan" wrote:

> Oh, I see the problem. DataTable implements IEnumerable, so PSH flattens it
> and returns its contents on the pipeline instead of the collection itself.
> To avoid this, simply put a comma in front of the value you want to return,
> like so:
>
> return ,$table;
>
> This essentially creates an array that contains only $table -- PSH only
> flattens one level of enumerables, so $table is passed directly on the
> pipeline instead of its contents.
>
> -- Ryan Milligan
>
> "Janssen" <Janssen@discussions.microsoft.com> wrote in message
> news:C20EF777-C515-45CB-BFB6-436C09FC8222@microsoft.com...
> > Thanks for the info. I'm trying to return 17 rows of a table completely
> > intact to be used as the same table outside of the function. What i
> > notice
> > happening is that when it leaves the function, it still looks like
> > everything
> > is there, but i no longer have access to table.rows.count. It is
> > functioning
> > like an array instead of a datatable. Here's my function:
> > function load-table
> > {
> > [xml]$subnets = gc ~\Desktop\halls.xml
> > $table = New-Object system.Data.DataTable "subnets"
> > $col1 = New-Object system.data.DataColumn building
> > $col2 = New-Object system.data.DataColumn oc1, ([int])
> > $col3 = New-Object system.data.DataColumn oc2, ([int])
> > $col4 = New-Object system.data.DataColumn oc3, ([int])
> > $col5 = New-Object system.data.DataColumn oc4, ([int])
> > $col6 = New-Object system.data.DataColumn range
> > $table.columns.add($col1)
> > $table.columns.add($col2)
> > $table.columns.add($col3)
> > $table.columns.add($col4)
> > $table.columns.add($col5)
> > $table.columns.add($col6)
> > $i=0
> > $j= $subnets.subnets.subnet.length
> > $row = @()
> > while ($i -lt $j)
> > {
> > [array]$row += ""
> > $row[$i] = $table.newrow()
> > $row[$i].building = $subnets.subnets.subnet[$i].building
> > $row[$i].oc1 = $subnets.subnets.subnet[$i].octet1
> > $row[$i].oc2 = $subnets.subnets.subnet[$i].octet2
> > $row[$i].oc3 = $subnets.subnets.subnet[$i].octet3
> > $row[$i].oc4 = $subnets.subnets.subnet[$i].octet4
> > $row[$i].range = $subnets.subnets.subnet[$i].sub
> > $table.rows.add($row[$i])
> > $i++
> > }
> > Write-Host $table.rows.count
> > return $table
> > }
> >
> > $table
> > $table.rows.count
> >
> > $table.rows.count returns "17" inside the function, but nothing outside
> > the
> > function. In fact, though all the data is still there, $table.rows no
> > longer
> > exists.
> >
> > I hope that makes some sense.
> >
> > Thanks for your help.
> >
> > Janssen
> >
> >
> >
> > "Janssen" wrote:
> >
> >> Hello. I've written a routine that writes an XML file into a Data Table
> >> ([system.Data.DataTable]), and it performs exactly the way I want it to,
> >> but
> >> when i put the routine inside a function and try to return the table at
> >> the
> >> end by using "return $table", it loses the datatype of
> >> [system.Data.DataTable]. It becomes an array. I can verify this by
> >> running
> >> $table.gettype() before and after it exits the function. Before the
> >> return,
> >> it says System.Data.DataRow. After the return, it says System.Array.
> >> I've
> >> tried forcing it by saying [System.Data.Table]$table = loadtable but it
> >> errors with the following message:
> >> Cannot convert "System.Object[]" to "System.Data.DataTable".
> >> You cannot call a method on a null-valued expression.
> >>
> >> So really, my question is, in Powershell, can you tell a function to
> >> return
> >> it's data as a specific data type? Any help would be appreciated.
> >>
> >> Thanks!
> >>
> >> Janssen Jones
> >>
>
>
>

That worked! Thanks a million. I've had trouble with "," and arrays before,
but I missed that this time....

Thanks again for such a fast response.

Janssen