As you may already know, it is possible to use the Execute SQL Task to populate a package variable with a result set.
In case you’re not that familiar with this technique yet, here are a quick two words on setting that up. You just give it a query, set the ResultSet property to Full result set and configure a package variable in the Result Set property window. The package variable’s type is System.Object.
But what exactly is this mysterious System.Object and how can we explore it? Well, that depends. More precisely, it depends on the Connection Type which you’ve chosen in the Execute SQL Task properties.
Let’s explore two possibilities: ADO.NET and OLE DB. Our end goal is straightforward: retrieve the number of records in the result set.
The query which I’m using in the Execute SQL task is this one:
select ProductAlternateKey from dbo.DimProduct where Color = 'blue'
On my AdventureWorksDW2012 database it should return 28 records:
Exploring the ADO.NET result set
The first step is finding out what type exactly this result set object is. Hook up a Script Task to your Execute SQL task and put a breakpoint on it. Now run your package and examine the Locals window:
Well look at that, it’s a System.Data.DataSet! Using this knowledge it’s fairly simple to produce code that fetches the record count:
DataSet ds = (DataSet)Dts.Variables["MyResultset"].Value; MessageBox.Show(ds.Tables.Rows.Count.ToString());
Note: don’t forget to add the package variable to the ReadOnlyVariables before opening the code editor.
The System.Data namespace is included by default in the using statements, no worries there. So we can just cast the variable into a Dataset. The DataSet object contains a DataTableCollection called Tables. As there’s only one result set this is located at index zero. We travel down the object tree to finally find the Count property of the Rows DataRowCollection.
And here’s the result:
That’s all there’s to it, easy huh? Let’s move on to our second option, OLE DB.
Exploring the OLE DB result set
Once again we start at the beginning: with the debugging of the Control Flow to find out what object type our mysterious System.Object is:
Hmm, System.__ComObject, that’s … special. Ow right, the OLE DB provider uses a COM wrapper. How can we “unwrap” our object and introduce it to the .NET world? Let’s see if we can find out what’s hidden behind that wrapper, by using the following code:
TypeName is a VB.NET function and retrieves the data type of the parameter passed into it.
To get this to run in a C# SSIS task you first need to add the Microsoft.VisualBasic reference:
Executing the package results in this:
So, our result is Recordset, hmm, well, I think we more or less knew this already. What kind of Recordset? Well, an ADO Recordset. We know this because the following code works:
System.Data.OleDb.OleDbDataAdapter da = new System.Data.OleDb.OleDbDataAdapter(); DataTable dt = new DataTable(); da.Fill(dt, Dts.Variables["MyResultset"].Value); MessageBox.Show(dt.Rows.Count.ToString());
Basically, we use the Fill method of the OleDbDataAdapter to fill a System.Data.DataTable with the data from the ADO Recordset. The version of the method in our example (there are several overrides) accepts two parameters:
public int Fill(
With the DataTable filled we’ve got once again access to a Rows DataRowsCollection, exactly the same as in our ADO.NET example in fact. Executing the package now results in exactly the same message box as shown earlier: 28 records!
Beware of pitfalls
If you mix the two methods up you’ll get funky errors such as:
System.InvalidCastException: Unable to cast COM object of type ‘System.__ComObject’ to class type ‘System.Data.DataSet’. Instances of types that represent COM components cannot be cast to types that do not represent COM components; however they can be cast to interfaces as long as the underlying COM component supports QueryInterface calls for the IID of the interface.
System.ArgumentException: Object is not an ADODB.RecordSet or an ADODB.Record.
So be careful, use the right object types for your particular System.Object.
In this article I’ve demonstrated a couple of methods which can be used to retrieve information from the mysterious System.Object result set in an SSIS package.