Création d'un DataReader (ADO.NET)
Les classes DataTable et DataSet ont une méthode CreateDataReader qui retourne le contenu de la collection Tables de l'objet DataTable ou de l'objet DataSet sous la forme d'un ou plusieurs jeux de résultats en lecture seule et en avant uniquement.
Exemple
L'application console suivante crée une instance de l'objet DataTable. Cet exemple passe ensuite le DataTable rempli à une procédure qui appelle la méthode CreateDataReader qui itère au sein des résultats contenus dans DataTableReader.
Private Sub TestCreateDataReader(ByVal dt As DataTable)
' Given a DataTable, retrieve a DataTableReader
' allowing access to all the tables's data:
Using reader As DataTableReader = dt.CreateDataReader()
Do
If Not reader.HasRows Then
Console.WriteLine("Empty DataTableReader")
Else
PrintColumns(reader)
End If
Console.WriteLine("========================")
Loop While reader.NextResult()
End Using
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 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 TestCreateDataReader(DataTable dt)
{
// Given a DataTable, retrieve a DataTableReader
// allowing access to all the tables' data:
using (DataTableReader reader = dt.CreateDataReader())
{
do
{
if (!reader.HasRows)
{
Console.WriteLine("Empty DataTableReader");
}
else
{
PrintColumns(reader);
}
Console.WriteLine("========================");
} while (reader.NextResult());
}
}
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 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();
}
}
L'exemple affiche la sortie suivante dans la fenêtre de console :
1 Mary
2 Andy
3 Peter
4 Russ