Navegar DataTables
O DataTableReader obtém o conteúdo de um ou mais objetos DataTable na forma de um ou mais conjuntos de resultados somente leitura de somente avanço.
Um DataTableReader poderá conter vários conjuntos de resultados se ele for criado com o método CreateDataReader. Quando há mais de um conjunto de resultados, o método NextResult avança o cursor para o próximo conjunto de resultados. Esse é um processo somente de encaminhamento. Não é possível retornar a um conjunto de resultados anterior.
Exemplo
No exemplo a seguir, o método TestConstructor cria duas instâncias de DataTable. Para demonstrar esse construtor para a classe DataTableReader, o exemplo cria um DataTableReader com base em uma matriz que contém as duas DataTables e executa uma operação simples, imprimindo o conteúdo das primeiras colunas na janela do console.
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