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CHAPTER 8 s INTRODUCING DATASETS AND DATA ADAPTERS
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InsertCommand Property
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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 would be searched for and propagated to the database.
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Try It Out: Propagating New Dataset Rows to a Data Source Let s propagate a new row to the database, in another variation on Listing 8-4. 1. Add a new Console Application project named PersistAdds to your 08 solution. 2. Replace the code in Module1.vb with the code in Listing 8-6. (This is a variation on Listing 8-4, with the nullability and insertion logic removed since they re irrelevant here.)
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Listing 8-6. PersistAdds: Module1.vb
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Imports System Imports System.Data Imports System.Data.SqlClient Module Module1 Sub Main() ' Set up connection string Dim connString As String = _ "server = .\sqlexpress;" _ & "integrated security = true;" _ & "database = northwind" ' Set up query Dim qry As String = _ "select " _ & " * " _ & "from " _ & " employees " _ & "where " _ & " country = 'UK' "
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CHAPTER 8 s INTRODUCING DATASETS AND DATA ADAPTERS
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' Set up DML Dim ins As String = _ "insert into employees " _ & "( " _ & " firstname, " _ & " lastname, " _ & & & & & & & & & & & & " titleofcourtesy, " _ " city, " _ " country " _ ") " _ "values " _ "( " _ " @firstname, " _ " @lastname, " _ " @titleofcourtesy, " _ " @city, " _ " @country " _ ") "
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' Create connection Dim conn As SqlConnection = New SqlConnection(connString) Try ' Create data adapter Dim da As SqlDataAdapter = New SqlDataAdapter(qry, conn) ' Create and fill dataset Dim ds As DataSet = New DataSet() da.Fill(ds, "employees") ' Get the 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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CHAPTER 8 s INTRODUCING DATASETS AND DATA ADAPTERS
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' Display rows in data table For Each row As DataRow In dt.Rows Console.WriteLine( _ "{0} {1} {2}", _ row("firstname").ToString().PadRight(15), _ row("lastname").ToString().PadLeft(25), _ row("city")) Next ' Insert Employees ' ' Create command Dim cmd As SqlCommand = New SqlCommand(ins, conn) ' ' Map parameters ' cmd.Parameters.Add( _ "@firstname", _ SqlDbType.NVarChar, _ 10, _ "firstname") cmd.Parameters.Add( _ "@lastname", _ SqlDbType.NVarChar, _ 20, _ "lastname") cmd.Parameters.Add( _ "@titleofcourtesy", _ SqlDbType.NVarChar, _ 25, _ "titleofcourtesy") cmd.Parameters.Add( _ "@city", _ SqlDbType.NVarChar, _ 15, _ "city") cmd.Parameters.Add( _ "@country", _ SqlDbType.NVarChar, _ 15, _ "country") '
CHAPTER 8 s INTRODUCING DATASETS AND DATA ADAPTERS
' Update database da.InsertCommand = cmd da.Update(ds, "employees") Catch e As Exception ' Display error Console.WriteLine("Error: " & e.ToString) Finally ' Close connection conn.Close() End Try End Sub End Module
3. Make this the startup project, and run it with Ctrl+F5. You should see the result in Figure 8-8.
Figure 8-8. Adding a row
How It Works You added an INSERT statement and changed the name of the original query string variable from sql to ins in order to clearly distinguish it from this statement:
' Set up DML Dim ins As String = _ "insert into employees " _ & "( " _ & " firstname, " _ & " lastname, " _ & " titleofcourtesy, " _ & " city, " _ & " country " _ & ") " _ & "values " _ & "( " _ & " @firstname, " _
CHAPTER 8 s INTRODUCING DATASETS AND DATA ADAPTERS
& & & & &
" @lastname, " _ " @titleofcourtesy, " _ " @city, " _ " @country " _ ") "
You replaced 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 insert SQL variable (ins), not the query one (sql).
' Insert Employees ' ' Create command Dim cmd As SqlCommand = New SqlCommand(ins, conn)
Then you configured the command parameters. The five columns for which you provided values are each mapped to a named command parameter. You didn t supply the primary key value since it s generated by SQL Server, and the other columns are nullable, so you didn t have to provide values for them. Note that all the values are current values, so you didn t have to specify the SourceVersion property.
' Map parameters ' cmd.Parameters.Add( _ "@firstname", _ SqlDbType.NVarChar, _ 10, _ "firstname") cmd.Parameters.Add( _ "@lastname", _ SqlDbType.NVarChar, _ 20, _ "lastname") cmd.Parameters.Add( _ "@titleofcourtesy", _ SqlDbType.NVarChar, _ 25, _ "titleofcourtesy") cmd.Parameters.Add( _ "@city", _ SqlDbType.NVarChar, _ 15, _ "city")
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