vb.net qr code generator free Figure 13-7. Modifying a row in Visual Basic .NET

Creator Data Matrix in Visual Basic .NET Figure 13-7. Modifying a row

Figure 13-7. Modifying a row
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You add an UPDATE statement and change the name of the original query string variable from sql to upd in order to clearly distinguish it from this statement: 'SQL to update employees Dim upd As String = "update employees " & _ "set city = @city " & _ "where employeeid = @employeeid" You replace the update comment in the try block with quite a bit of code. Let s look at it piece by piece. Creating a command is nothing new, but notice that you use the update SQL variable (upd), not the query one (sql): ' update Employees ' ' create command Dim cmd As New SqlCommand(upd, conn) Then you configure the command parameters. The @city parameter is mapped to a data column named city. Note that you don t specify the data table, but you must be sure the type and length are compatible with this column in whatever data table you eventually use: ' City cmd.Parameters.Add("@city", SqlDbType.NVarChar, 15, "city")
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CHAPTER 13 s USING DATASETS AND DATA ADAPTERS
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Next, you configure the @employeeid parameter, mapping it to a data column named employeeid. Unlike @city, which by default takes values from the current version of the data table, you want to make sure that @employeeid gets values from the version before any changes. Although it doesn t matter here, since you don t change any employee IDs, it s a good habit to specify the original version for primary keys, so if they do change, the correct rows are accessed in the database table. Note also that you save the reference returned by the Add method so you can set its SourceVersion property. Since you don t need to do anything else with @city, you don t have to save a reference to it. ' EmployeeID Dim parm As SqlParameter = cmd.Parameters.Add _ ("@employeeid", SqlDbType.Int, 4, "employeeid") parm.SourceVersion = DataRowVersion.Original Finally, you set the data adapter s UpdateCommand property with the command to update the Employees table so it will be the SQL the data adapter executes when you call its Update method. You then call Update on the data adapter to propagate the change to the database. Here you have only one change, but since the SQL is parameterized, the data adapter will look for all changed rows in the employees data table and submit updates for all of them to the database. ' Update database da.UpdateCommand = cmd da.Update(ds, "employees") Figure 13-7 shows the change to the city, and if you check with Database Explorer or SSMSE, you ll see the update has been propagated to the database. The city for employee Steven Buchanan is now Wilmington, not London.
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The data adapter uses the InsertCommand property for inserting rows into a table. Upon calling the Update method, all rows added to the data table will be searched for and propagated to the database.
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Try It Out: Propagating New Dataset Rows to a Data Source
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Let s propagate a new row to the database, in another variation on ModifyDataTable.vb in Listing 13-4. 1. Add a new Visual Basic Console Application project named PersistAdds to your 13 solution. Rename Module1.vb to PersistAdds.vb. 2. Replace the code in PersistAdds.vb with the code in Listing 13-6.
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CHAPTER 13 s USING DATASETS AND DATA ADAPTERS
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Listing 13-6. PersistAdds.vb Imports System Imports System.Data Imports System.Data.SqlClient Module PersistAdds Sub Main() Dim connstring As String = _ ("Data Source=.\sqlexpress;" & _ "Integrated Security=True;" & _ "database=northwind") 'query Dim qry As String = "select * from employees " & _ "where country = 'UK'" 'SQL to insert employees Dim ins As String = "insert into employees " & _ "(firstname,lastname,titleofcourtesy,city,country)" & _ "values(@firstname,@lastname,@titleofcourtesy,@city,@country)" 'create connection Dim conn As SqlConnection = New SqlConnection(connstring) Try ' create data adapter Dim da As New SqlDataAdapter() da.SelectCommand = New SqlCommand(qry, conn) ' create and fill dataset Dim ds As New DataSet() da.Fill(ds, "employees") ' get data table reference Dim dt As DataTable = ds.Tables("employees") ' add a row Dim newRow As DataRow = dt.NewRow() newRow("firstname") = "Roy" newRow("lastname") = "Beatty" newRow("titleofcourtesy") = "Sir" newRow("city") = "Birmingham" newRow("country") = "UK" dt.Rows.Add(newRow)
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