DataTable の移動 (ADO.NET)
DataTableReader は、1 つ以上の DataTable オブジェクトの内容を、読み取り専用、前方参照専用の 1 つ以上の結果セットとして取得します。
CreateDataReader メソッドの呼び出しにより DataTableReader を作成した場合、DataTableReader に複数の結果セットが含まれる場合があります。 結果セットが複数ある場合、NextResult メソッドは、カーソルを次の結果セットに移動します。 これは前方参照専用です。 前の結果セットに戻ることはできません。
例
2 つの DataTable インスタンスを作成する TestConstructor メソッドの例を次に示します。 DataTableReader クラスを対象としたこのコンストラクターを示すために、この例では、2 つの DataTables が含まれる配列に基づいた新しい DataTableReader を作成し、単純な操作を実行して、最初の 2 ～ 3 列の内容をコンソール ウィンドウに表示します。
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();
}
}