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Hiermee DataTableReader haalt u de inhoud van een of meer DataTable objecten op in de vorm van een of meer alleen-lezen resultatensets.

Een DataTableReader kan meerdere resultatensets bevatten als deze wordt gemaakt met behulp van de CreateDataReader methode. Wanneer er meer dan één resultatenset is, gaat de NextResult methode de cursor naar de volgende resultatenset. Dit is een proces voor alleen-doorsturen. Het is niet mogelijk om terug te keren naar een vorige resultatenset.

Opmerking

In het volgende voorbeeld maakt de TestConstructor methode twee DataTable exemplaren. Om deze constructor voor de DataTableReader klasse te demonstreren, maakt het voorbeeld een nieuwe DataTableReader op basis van een matrix die de twee DataTables bevat en voert een eenvoudige bewerking uit, waarbij de inhoud van de eerste paar kolommen naar het consolevenster wordt afgedrukt.

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(
               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();
}

static DataTable GetCustomers()
{
    // Create sample Customers table, in order
    // to demonstrate the behavior of the DataTableReader.
    DataTable table = new();

    // 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;
}

static DataTable GetProducts()
{
    // Create sample Products table, in order
    // to demonstrate the behavior of the DataTableReader.
    DataTable table = new();

    // 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;
}

static void PrintColumns(DataTableReader reader)
{
    // Loop through all the rows in the DataTableReader
    while (reader.Read())
    {
        for (var i = 0; i < reader.FieldCount; i++)
        {
            Console.Write(reader[i] + " ");
        }
        Console.WriteLine();
    }
}

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

Zie ook