Webcast: Live From Redmond - VB9, Building N-Tier Applications

youngjoo — Tue, 22 May 2007 02:52:00 GMT

My second webcast which was a part of the webcast series done by Visual Basic Team called "Live From Redmond" webcasts on Visual Studio "Orcas" was on building N-Tier application using Visual Studio "Orcas". I gave this webcast a couple of weeks ago and it wasn't until today that on-demand version became available. Sorry to those who have been waiting for the on-demand link and a copy of my slide.

During this webcast, I described new "Orcas" data features at high-level and built a simple multi-tiered application as a demonstration. Specific topics that I covered include:

Hierarchical Update Support in Typed Dataset

TableAdapterManager class and TableAdapterManager.UpdateAll() method

N-Tier Support in Typed Dataset

Dataset Designer support to make Typed Dataset N-Tier friendly
How to add custom validation logic to Typed Dataset and apply them through multiple tiers

How to create and consume basic WCF service

LINQ to Typed Dataset

You can watch this webcast on-demand by visiting following Microsoft Events page. Also, a link to my slide deck below.

TableAdapter’s RETURN_VALUE mystery

youngjoo — Wed, 26 Jul 2006 02:07:00 GMT

If you've been trying to figure out why you cannot access the return value when using stored procedures in TableAdapter, here's the answer and the solution for you.

Assume I added a new query to my TableAdapter via Dataset Designer and named it ReturnSomething. For this query, I used a simple stored procedure that just returns an integer value. Without looking at the generated code, most people expect the return value of the generated query method to contain the return value of the stored procedure and try something like below:

Dim returnValue As Integer
returnValue = taQuery.ReturnSomething

However, above call results in either compile error or run-time error. The problem is that these query methods actually return something else depending on what option you chose for 'Choose the shape of date returned by the stored procedure' dialog when adding your query via TableAdapter Query Configuration Wizard.

Single value: Query method returns the value of the first column of the first row in the result set returned by SELECT statement in your stored procedure. If SELECT statement returns nothing or if there's no SELECT statement, then the return value is NULL.
No value: Query method returns the number of rows affected by the stored procedure.

Definitely not the return value from the stored procedure. If you look at the generated code, this all makes sense. Here's the example code for these methods.

'' Singe value

Public Overloads Overridable Function ReturnSomethingSingleValue(ByVal MyParam As System.Nullable(Of Integer)) As Object

...

Dim returnValue As Object

Try

returnValue = command.ExecuteScalar

Finally

If (previousConnectionState = System.Data.ConnectionState.Closed) Then

command.Connection.Close

End If

End Try

If ((returnValue Is Nothing) _

OrElse (returnValue.GetType Is GetType(System.DBNull))) Then

Return Nothing

Else

Return CType(returnValue,Object)

End If

End Function

'' No value

Public Overloads Overridable Function ReturnSomethingNoValue(ByVal MyParam As System.Nullable(Of Integer)) As Integer

...

Dim returnValue As Integer

Try

returnValue = command.ExecuteNonQuery

Finally

If (previousConnectionState = System.Data.ConnectionState.Closed) Then

command.Connection.Close

End If

End Try

Return returnValue

End Function

Notice that for single value query, ExecuteScalar method is used and for no value query ExecuteNonQuery method is used. And both query methods return what corresponding execute methods return. ExecuteScalar method returns, as described above, the value of the first column of the first row in the result set and ExecuteNonQuery returns the number of rows affected by the command.

Ok. It's very comforting to know what these methods return and we now understand where errors come from. But where do we get actual return values from then? If you read through the generated code carefully, you will notice that TableAdapter actually has places for return values.

Private Sub InitCommandCollection()

...

CType(Me._commandCollection(0),System.Data.SqlClient.SqlCommand).CommandText = "dbo.ReturnSomething"

...

CType(Me._commandCollection(0),System.Data.SqlClient.SqlCommand).Parameters.Add(New System.Data.SqlClient.SqlParameter("@RETURN_VALUE", System.Data.SqlDbType.Int, 4, System.Data.ParameterDirection.ReturnValue, 10, 0, Nothing, System.Data.DataRowVersion.Current, false, Nothing, "", "", ""))

...

CType(Me._commandCollection(1),System.Data.SqlClient.SqlCommand).CommandText = "dbo.ReturnSomething"

...

CType(Me._commandCollection(1),System.Data.SqlClient.SqlCommand).Parameters.Add(New System.Data.SqlClient.SqlParameter("@RETURN_VALUE", System.Data.SqlDbType.Int, 4, System.Data.ParameterDirection.ReturnValue, 10, 0, Nothing, System.Data.DataRowVersion.Current, false, Nothing, "", "", ""))

...

End Sub

As you can see from above code sample, each SqlCommand object has ReturnValue parameter in its Parameters collection. So, it's just a matter of retrieving these values after you execute your query method. To demonstrate how this can be done, I wrote below code in partial class. Note that this is very simple code sample that has no error handling or validation. It just demonstrates the idea.

Namespace MyDatasetTableAdapters

Partial Class QueriesTableAdapter

Public Function GetReturnValue(ByVal commandIndex As Integer) As Object

Return Me.CommandCollection(commandIndex).Parameters(0).Value

End Function

End Class

End Namespace

After you add above code to your partial class, you can retrieve return value of specific command by doing something like below.

Dim taQueries As MyDatasetTableAdapters.QueriesTableAdapter

Dim returnValue As Integer

Dim myInputParam As Integer

myInputParam = 999

taQueries = New MyDatasetTableAdapters.QueriesTableAdapter()

taQueries.ReturnSomethingSingleValue(myInputParam)

returnValue = taQueries.GetReturnValue(0)

Above code will execute the first query method in the commandCollection and retrieve the return value of the same command via GetReturnValue method added to the partial class. Notice that 0 is passed as the parameter value for GetReturnValue method to specify that we want to retrieve the return value for the first command in the collection. Yeah, it's ugly. But, again, you get the idea. :)

Typed Dataset simplifies your data access coding. But there are many things that you might not be able to do using generated Typed Dataset. If you are faced with that situation, look for ways to leverage partial classes to add/modify Typed Dataset behavior. That's exactly why we added partial class in Visual Studio 2005!

If you have better ways to handle return values, please let me know. See something wrong with above approach? Don't be afraid to send me hate email! :)

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Webcast: Live From Redmond - VB9, Building N-Tier Applications

TableAdapter’s RETURN_VALUE mystery