Iterating over multiple rows of data in PowerShell

Question

I'm writing some PowerShell code to connect to a database, read multiple rows of data, and return them back via a SqlDataReader.

I did this "the C# way" by writing it how I would write this in C#:

function ExecuteQuery($sql) {
    $connection = new-object system.data.SqlClient.SQLConnection($ConnectionString);
    $connection.Open();

    $cmd = $connection.CreateCommand();
    $cmd.CommandText = $sql;
    $cmd.Connection = $connection    
    $reader = [System.Data.SqlClient.SqlDataReader]$cmd.ExecuteReader()
    return $reader;
}

(The caller of this function has to close the connection themselves responsibly.)

I expected, even without the typecast, that I would get an instance of System.Data.SqlClient.SqlDataReader. This is important, because I want to use Read to iterate through row by row, not to mention that I want to use square-brackets to access data by column name (accessing by ID is too fragile).

Unfortunately, I get back an instance of System.Data.Common.DataRecordInternal, which does not contain a Read method, nor does it allow me to access records by array index.

My question is: how can I read and iterate through multiple rows of data in PowerShell?

Answer 1

There's a couple of ways to iterate through members of an array ('rows of data' in your case). The first that comes to mind is:

ForEach($Record in (ExecuteQuery $CommandString){
    Do Stuff to $Record
}

Or you could pipe it to a ForEach loop (you can pipe output this way, such as to Out-File if desired):

ExecuteQuery $CommandString | ForEach{Do stuff to $_}

Or if you really want more granular control I suppose you could use a For loop and do something like:

$Results = ExecuteQuery $CommandString 
For($i=0;$i -le $Results.count;$i++){
    Do stuff to $Results[$i]
}

Answer 2

The problem is that PowerShell is trying to enumerate the reader for you when the function returns it. You can tell PowerShell to leave it alone by putting it into an array:

return ,$reader