Navigation DataTables (ADO.NET)
L'objet DataTableReader obtient le contenu d'un ou plusieurs objets DataTable sous la forme d'un ou plusieurs jeux de résultats en lecture seule et en avant uniquement.
Un objet DataTableReader peut contenir plusieurs jeux de résultats s'il est créé à l'aide de la méthode CreateDataReader. S'il y a plusieurs jeux de résultats, la méthode NextResult déplace le curseur sur le jeu de résultats suivant. Il s'agit d'un processus en avant uniquement. Il n'est pas possible de revenir à un jeu de résultats précédent.
Exemple
Dans l'exemple suivant, la méthode TestConstructor crée deux instances de DataTable . Pour montrer ce constructeur pour la classe DataTableReader, l'exemple crée un nouveau DataTableReader basé sur un tableau contenant les deux DataTables et effectue une opération simple, en imprimant le contenu de quelques-unes des premières colonnes sur la fenêtre de console.
Private Sub TestConstructor()
' Create two data adapters, one for each of the two
' DataTables to be filled.
Dim customerDataTable As DataTable = GetCustomers()
Dim productDataTable As DataTable = GetProducts()
' Create the new DataTableReader.
Using reader As New DataTableReader( _
New DataTable() {customerDataTable, productDataTable})
' Print the contents of each of the result sets.
Do
PrintColumns(reader)
Loop While reader.NextResult()
End Using
Console.WriteLine("Press Enter to finish.")
Console.ReadLine()
End Sub
Private Function GetCustomers() As DataTable
' Create sample Customers table, in order
' to demonstrate the behavior of the DataTableReader.
Dim table As New DataTable
' Create two columns, ID and Name.
Dim idColumn As DataColumn = table.Columns.Add("ID", GetType(Integer))
table.Columns.Add("Name", GetType(String))
' Set the ID column as the primary key column.
table.PrimaryKey = New DataColumn() {idColumn}
table.Rows.Add(New Object() {1, "Mary"})
table.Rows.Add(New Object() {2, "Andy"})
table.Rows.Add(New Object() {3, "Peter"})
table.Rows.Add(New Object() {4, "Russ"})
Return table
End Function
Private Function GetProducts() As DataTable
' Create sample Products table, in order
' to demonstrate the behavior of the DataTableReader.
Dim table As New DataTable
' Create two columns, ID and Name.
Dim idColumn As DataColumn = table.Columns.Add("ID", GetType(Integer))
table.Columns.Add("Name", GetType(String))
' Set the ID column as the primary key column.
table.PrimaryKey = New DataColumn() {idColumn}
table.Rows.Add(New Object() {1, "Wireless Network Card"})
table.Rows.Add(New Object() {2, "Hard Drive"})
table.Rows.Add(New Object() {3, "Monitor"})
table.Rows.Add(New Object() {4, "CPU"})
Return table
End Function
Private Sub PrintColumns( _
ByVal reader As DataTableReader)
' Loop through all the rows in the DataTableReader.
Do While reader.Read()
For i As Integer = 0 To reader.FieldCount - 1
Console.Write(reader(i).ToString() & " ")
Next
Console.WriteLine()
Loop
End Sub
private static void TestConstructor()
{
// Create two data adapters, one for each of the two
// DataTables to be filled.
DataTable customerDataTable = GetCustomers();
DataTable productDataTable = GetProducts();
// Create the new DataTableReader.
using (DataTableReader reader = new DataTableReader(
new DataTable[] { customerDataTable, productDataTable }))
{
// Print the contents of each of the result sets.
do
{
PrintColumns(reader);
} while (reader.NextResult());
}
Console.WriteLine("Press Enter to finish.");
Console.ReadLine();
}
private static DataTable GetCustomers()
{
// Create sample Customers table, in order
// to demonstrate the behavior of the DataTableReader.
DataTable table = new DataTable();
// Create two columns, ID and Name.
DataColumn idColumn = table.Columns.Add("ID", typeof(int));
table.Columns.Add("Name", typeof(String[]));
// Set the ID column as the primary key column.
table.PrimaryKey = new DataColumn[] { idColumn };
table.Rows.Add(new object[] { 1, "Mary" });
table.Rows.Add(new object[] { 2, "Andy" });
table.Rows.Add(new object[] { 3, "Peter" });
table.Rows.Add(new object[] { 4, "Russ" });
return table;
}
private static DataTable GetProducts()
{
// Create sample Products table, in order
// to demonstrate the behavior of the DataTableReader.
DataTable table = new DataTable();
// Create two columns, ID and Name.
DataColumn idColumn = table.Columns.Add("ID", typeof(int));
table.Columns.Add("Name", typeof(String[]));
// Set the ID column as the primary key column.
table.PrimaryKey = new DataColumn[] { idColumn };
table.Rows.Add(new object[] { 1, "Wireless Network Card" });
table.Rows.Add(new object[] { 2, "Hard Drive" });
table.Rows.Add(new object[] { 3, "Monitor" });
table.Rows.Add(new object[] { 4, "CPU" });
return table;
}
private static void PrintColumns(DataTableReader reader)
{
// Loop through all the rows in the DataTableReader
while (reader.Read())
{
for (int i = 0; i < reader.FieldCount; i++)
{
Console.Write(reader[i] + " ");
}
Console.WriteLine();
}
}