DataTableReader.HasRows 属性

定义

命名空间:

System.Data

程序集:

System.Data.Common.dll

Source:

DataTableReader.cs

获取一个值，该值指示 DataTableReader 是否包含一行还是多行。

public:
 virtual property bool HasRows { bool get(); };

public override bool HasRows { get; }

member this.HasRows : bool

Public Overrides ReadOnly Property HasRows As Boolean

属性值

Boolean

如果 DataTableReader 包含一行或多行，则为 true；否则为 false。

例外

InvalidOperationException

尝试检索有关已关闭的 DataTableReader 的信息。

示例

以下示例使用数据填充两个 DataTable 实例。 第一个 DataTable 包含一行，第二个包含没有行。 然后，该示例创建一个包含这两DataTable个 DataTableReader 对象的 ，并调用 PrintData 方法来显示每个对象的内容，在HasRows调用 PrintData 之前检查每个 对象的 属性值。

private static void TestHasRows()
{
    DataTable customerTable = GetCustomers();
    DataTable productTable = GetProducts();

    using (DataTableReader reader = new DataTableReader(
               new DataTable[] { customerTable, productTable }))
    {
        do
        {
            if (reader.HasRows)
            {
                PrintData(reader);
            }
        } while (reader.NextResult());
    }

    Console.WriteLine("Press Enter to finish.");
    Console.ReadLine();
}

private static void PrintData(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();
    }
}

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" });
    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 };
    return table;
}

Private Sub TestHasRows()
   'Retrieve one row from the Store table:
   Dim customerTable As DataTable = GetCustomers()
   Dim productsTable As DataTable = GetProducts()

   Using reader As New DataTableReader( _
      New DataTable() {customerTable, productsTable})

      Do
         If reader.HasRows Then
            PrintData(reader)
         End If
      Loop While reader.NextResult()
   End Using

   Console.WriteLine("Press Enter to finish.")
   Console.ReadLine()
End Sub

Private Sub PrintData( _
   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("{0} ", reader(i))
      Next
      Console.WriteLine()
   Loop
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"})
   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}

   Return table
End Function

注解

属性 HasRows 返回有关当前结果集的信息。 DataTableReader如果 包含多个结果集，则可以在调用 NextResult 方法后立即检查 属性的值HasRows，以确定新结果集是否包含行。

HasRows使用 属性可避免在当前结果集中没有行时调用 Read 的 方法DataTableReader的要求。

另请参阅

• NextResult()
• Read()