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DataColumn.Expression Property

  • Reference

Definition

Namespace:
System.Data
Assembly:
System.Data.Common.dll
Assembly:
System.Data.dll
Assembly:
netstandard.dll
Source:
DataColumn.cs
Source:
DataColumn.cs
Source:
DataColumn.cs

Gets or sets the expression used to filter rows, calculate the values in a column, or create an aggregate column.

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

Property Value

String

An expression to calculate the value of a column, or create an aggregate column. The return type of an expression is determined by the DataType of the column.

Attributes
DataSysDescriptionAttribute

Exceptions

ArgumentException

The AutoIncrement or Unique property is set to true.

FormatException

When you are using the CONVERT function, the expression evaluates to a string, but the string does not contain a representation that can be converted to the type parameter.

InvalidCastException

When you are using the CONVERT function, the requested cast is not possible. See the Conversion function in the following section for detailed information about possible casts.

ArgumentOutOfRangeException

When you use the SUBSTRING function, the start argument is out of range.

-Or-

When you use the SUBSTRING function, the length argument is out of range.

Exception

When you use the LEN function or the TRIM function, the expression does not evaluate to a string. This includes expressions that evaluate to Char.

Examples

The following example creates three columns in a DataTable. The second and third columns contain expressions; the second calculates tax using a variable tax rate, and the third adds the result of the calculation to the value of the first column. The resulting table is displayed in a DataGrid control.

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

Remarks

For more information about this API, see Supplemental API remarks for DataColumn.Expression.

Applies to

See also