Using Stored Procedures in Conjuction with DataAdapter

Public Function GetPubInfo() As DataSet
daPubs.Fill(dsPubs)
Return dsPubs
End Function

Note: Error handling has been omitted for clarity.

It is interesting to note that the fill method of the DataAdapter will implicitly open the connection and close it after retrieving the data. If you explicitly open the connection, however, the DataAdapter will not close it.

To test the method, place a DataGrid on Form1. Switch to the Code Editor Window and declare a private class level instance of the Publishers class and the DataSet class after the Inherits statement.

Public Class Form1
Inherits System.Windows.Forms.Form
Private objPublishers As Publishers
Private dsPubInfo As DataSet

In the Forms constructor code instantiate a new instance of the Publishers class. Set dsPubInfo to the DataSet returned by calling the GetPubInfo method of the Publishers class. Set the DataSource property of the DataGrid to the first (and only) table in the dsPubInfo tables collection.

Public Sub New()
MyBase.New()
'This call is required by the Windows Form Designer.
InitializeComponent()
'Add any initialization after the InitializeComponent() call
objPublishers = New Publishers
dsPubInfo = objPublishers.GetPubInfo
Me.DataGrid1.DataSource = dsPubInfo.Tables(0)
End Sub

Run the application in the debugger and verify that the results are displayed in the grid.

Updating Data Using the SQLDataAdapter in Conjunction with a Stored Procedure

In addition to the SelectCommand property, the SQLDataAdapter object includes the UpdateCommand, InsertCommand, and the DeleteCommand properties. The Update method of the SQLDataAdapter will call the appropriate SQLCommand object for each updated, inserted, or deleted DataRow in the DataTable passed with the update call. When updating data, input parameters pass the values of the updated fields to the stored procedure.

The SQLParameter class encapsulates properties and methods for working with parameters. The SQLParameter class includes properties such as the ParameterName, SqlDBType, Direction, Size, Value, SourceColumn, and SourceVersion. The ParameterName, SqlDBType, Direction and Size properties are set to match the parameter definition in the stored procedure. For example, the following code creates a parameter object that matches the @pub_id parameter in the up_UpdatePubInfo stored procedure created previously.

Dim UpdParam As New SqlParameter("@pub_id", SqlDbType.Char, 4)

In this case, an overloaded constructor of the SqlParameter class sets the appropriate properties. Although the Direction property has not been explicitly set, Input is the default. If the parameter direction is InputOutput, Output, or a ReturnValue, the direction must be explicitly set. For example, the following code is used to explicitly set the Direction property of a SqlParameter object.

oParam.Direction = ParameterDirection.Output

The SourceColumn property maps a DataColumn from the DataTable passed in when you call the Update method of the SqlDataAdapter object. This mapping allows the implicit loading of the SqlParameters Value property from the DataTable during updates. If you do not set the SourceColumn, the Value property of the SqlParameter object must be explicitly set in code.

The SourceVersion is a useful property that defaults to a value of Current. This value is the current value of the field in the DataRow and is the value that you intend to update to the database. The SourceVersion of a SqlParameter object can also be set to a value of Original. This is the value of the field when the DataTable was originally loaded from the database. Passing both of these values to a stored procedure allows for concurrency checking before the data update takes place. The following stored procedure uses the original value to check if another user has changed the data before updating.

CREATE PROCEDURE dbo.up_updPubName
( @pub_id char(4),
@pub_name varchar(40),
@Original_pub_name varchar(40)
)
AS
if exists(select pub_id from publishers
where (pub_id = @pub_id) AND
(pub_name = @Original_pub_name))
Begin
UPDATE publishers SET pub_name = @pub_name
WHERE (pub_id = @pub_id)
End

In order to execute this stored procedure, you define an @Original_pub_name SqlParameter object that uses the Original value of the field as its SourceVersion.

Dim UpdPubParam As New SqlParameter("@Original_pub_name", _SqlDbType.VarChar, 40)
UpdAuthParam.SourceColumn = "pub_name"
UpdAuthParam.SourceVersion = DataRowVersion.Original

Note: Concurrency issues in disconnected data scenarios are an important topic. Although only briefly mentioned in this article, a future article will explore these issues.

After defining a SqlParameter object for each parameter identified in the stored procedure, the SqlParameter objects are added to the Parameters collection of the SqlCommand object responsible for executing the stored procedure. The following code demonstrates adding a SqlParameter object to a Parameter collection.

cmdUpdPubInfo.Parameters.Add(UpdParam)

As an alternative, the overloaded Add method allows the creation of the SqlParameter object and its addition to the collection in one-step.

cmdUpdPubInfo.Parameters.Add("@pub_id", SqlDbType.Char, 4,"pub_id")

In order to demonstrate the process of using a SqlDataAdapter object in conjunction with a stored procedure to update data, open the Windows Application project you created earlier. Using the Server Explorer window create the up_UpdPubName stored procedure in the Pubs database. Open the Publishers class in the Code Editor and add the following class level declaration to create a SqlCommand object.

Private cmdUpdPubInfo As SqlCommand

In the body of the class constructor, add code to instantiate the update command and set the Connection, CommandType, and CommandText properties.

'Update command
cmdUpdPubInfo = New SqlCommand()
cmdUpdPubInfo.Connection = cnPubs
cmdUpdPubInfo.CommandType = CommandType.StoredProcedure
cmdUpdPubInfo.CommandText = "up_UpdPubName"

Next, define and add the necessary update parameters to the parameters collection.

'Update command parameters
cmdUpdPubInfo.Parameters.Add("@pub_id", SqlDbType.Char, 4, "pub_id")cmdUpdPubInfo.Parameters.Add("@pub_name", SqlDbType.VarChar, 40, pub_name")Dim UpdPubParam As New SqlParameter _("@Original_pub_name", SqlDbType.VarChar, 40, "pub_name")
UpdPubParam.SourceVersion = DataRowVersion.Original
cmdUpdPubInfo.Parameters.Add(UpdPubParam)

Add code after the DataAdapter instantiation to set the UpdateCommand property of the DataAdapter to the cmdUpdPubInfo object.

daPubs.UpdateCommand = cmdUpdPubInfo

Create a sub procedure called UpdatePubInfo that takes a DataSet object as an input parameter. In the body of the function, call the update method of the DataAdapter object passing in the DataSet.

Public Sub UpdatePubInfo(ByVal dsChanges As DataSet)
daPubs.Update(dsChanges)
End Sub

Add a button to Form1 and add code to the buttons update event that calls the UpdatePubInfo method of the objPublisher. First, check if the DataSet has changes by calling the HasChanges method. If there are changes, filter the dsPublisher and pass only the changed rows by calling the GetChanges method of the DataSet.

If dsPubInfo.HasChanges Then
objPublishers.UpdatePubInfo(dsPubInfo.GetChanges)
dsPubInfo.Clear()
dsPubInfo = objPublishers.GetPubInfo
End If

Run the application in debug mode. Make changes to the pub_name and click the update button. Stop the application. Right click publisher table node in the Server Explorer window and choose Retrieve Data from Table. Verify that the changes updated to the database.

Now that you are familiar with using a stored procedure to implement updating data through the SqlDataApapter, You can implement data inserts and deletes in a similar fashion. This will be an exercise left for the reader. The solution code accompanying this article will contain sample code demonstrating inserts and updates using the SqlDataAdapter.

Summary

This article demonstrated using the SqlDataAdapter class and its use of parameters when updating data back to the database. You also saw how to use the SqlDataAdapter in conjunction with stored procedures to propagate data changes in a disconnected DataSet back to the database. Encapsulating data update logic in stored procedures is an excellent way to improve the manageability, scalability, and security of your database driven applications. One area this article does not address is the issue of data concurrency. Dealing with data concurrency is vital in a disconnected scenario. Although only hinted at in this article, look for a future article that will discuss concurrency issues in detail.

Note: The code presented in this article is for demonstration purposes only. Proper error handling has been omitted for clarity.