DataColumn.Expression 属性

public:
 property System::String ^ Expression { System::String ^ get(); void set(System::String ^ value); };

public string Expression { get; set; }

[System.Data.DataSysDescription("DataColumnExpressionDescr")]
public string Expression { get; set; }

member this.Expression : string with get, set

[<System.Data.DataSysDescription("DataColumnExpressionDescr")>]
member this.Expression : string with get, set

Public Property Expression As String

用来计算列的值，或创建聚合列的表达式。 表达式的返回类型由列的 DataType 来确定。

属性

DataSysDescriptionAttribute

以下示例在 中创建三列 DataTable。 第二列和第三列包含表达式：第二个使用可变税率计算税收，第三个将计算结果添加到第一列的值。 生成的表显示在 控件 DataGrid 中。

private void CalcColumns()
{
    DataTable table = new DataTable ();

    // Create the first column.
    DataColumn priceColumn = new DataColumn();
    priceColumn.DataType = System.Type.GetType("System.Decimal");
    priceColumn.ColumnName = "price";
    priceColumn.DefaultValue = 50;

    // Create the second, calculated, column.
    DataColumn taxColumn = new DataColumn();
    taxColumn.DataType = System.Type.GetType("System.Decimal");
    taxColumn.ColumnName = "tax";
    taxColumn.Expression = "price * 0.0862";

    // Create third column.
    DataColumn totalColumn = new DataColumn();
    totalColumn.DataType = System.Type.GetType("System.Decimal");
    totalColumn.ColumnName = "total";
    totalColumn.Expression = "price + tax";

    // Add columns to DataTable.
    table.Columns.Add(priceColumn);
    table.Columns.Add(taxColumn);
    table.Columns.Add(totalColumn);

    DataRow row = table.NewRow();
    table.Rows.Add(row);
    DataView view = new DataView(table);
    dataGrid1.DataSource = view;
}

Private Sub CalcColumns()
     Dim rate As Single = .0862
     Dim table As New DataTable()
 
     ' Create the first column.
     Dim priceColumn As New DataColumn()
     With priceColumn
         .DataType = System.Type.GetType("System.Decimal")
         .ColumnName = "price"
         .DefaultValue = 50
     End With
     
     ' Create the second, calculated, column.
     Dim taxColumn As New DataColumn()
     With taxColumn
         .DataType = System.Type.GetType("System.Decimal")
         .ColumnName = "tax"
         .Expression = "price * 0.0862"
     End With
     
    ' Create third column
     Dim totalColumn As New DataColumn()
     With totalColumn
         .DataType = System.Type.GetType("System.Decimal")
         .ColumnName = "total"
         .Expression = "price + tax"
     End With
 
     ' Add columns to DataTable
     With table.Columns
         .Add(priceColumn)
         .Add(taxColumn)
         .Add(totalColumn)
     End With
    
     Dim row As DataRow= table.NewRow
     table.Rows.Add(row)
     Dim view As New DataView
     view.Table = table
     DataGrid1.DataSource = view
 End Sub

有关此 API 的详细信息，请参阅 DataColumn.Expression 的补充 API 说明。

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