DataColumn.Expression in with DateTime

[SavantMan]

I'm trying to do something that seems like it should be pretty simple, but haven't found a solution. I am trying to add a datacolumn to a datatable that adds or subtracts a number of days based on another datetime column in the table. See sample below. How do I do this? Any help would be greatly appreciated. Thanks

   Private Sub CreateDataTable()
      dt = New DataTable

      Dim IntegerColumn As New DataColumn
      IntegerColumn.DataType = GetType(Integer)
      IntegerColumn.ColumnName = "IntegerColumn"
      dt.Columns.Add(IntegerColumn)

      Dim ComputedIntegerColumn As New DataColumn
      ComputedIntegerColumn.DataType = GetType(Integer)
      ComputedIntegerColumn.ColumnName = "ComputedIntegerColumn"
      ComputedIntegerColumn.Expression = "IntegerColumn + 2"
      dt.Columns.Add(ComputedIntegerColumn)

      Dim DateColumn As New DataColumn
      DateColumn.DataType = GetType(System.DateTime)
      DateColumn.ColumnName = "DateColumn"
      dt.Columns.Add(DateColumn)

      Dim ComputedDateColumn As New DataColumn
      ComputedDateColumn.DataType = GetType(System.DateTime)
      ComputedDateColumn.ColumnName = "ComputedDateColumn"
      ComputedDateColumn.Expression = "DateColumn.AddDays(2)"  ' this doesn't work
      ComputedDateColumn.Expression = "DateColumn + 2"         ' this doesn't work either
      dt.Columns.Add(ComputedDateColumn)

      Dim r As DataRow = dt.NewRow
      r.Item("IntegerColumn") = 5
      r.Item("DateColumn") = Date.Today

      dt.Rows.Add(r)

   End Sub

 

[RonRepp]

try this:

Dim ComputedDateColumn As New DataColumn
      ComputedDateColumn.DataType = GetType(System.DateTime)
      ComputedDateColumn.ColumnName = "ComputedDateColumn"
      ComputedDateColumn.Expression = DateAdd("d",2,cdate("DateColumn"))       
      dt.Columns.Add(ComputedDateColumn)

I hope this works.

Ron Repp

If gray hair is a sign of wisdom, then I'm a genius.

 

[SavantMan]

Ron,

The expression property is a string so :

ComputedDateColumn.Expression = DateAdd("d",2,cdate("DateColumn"))

must actually be:

ComputedDateColumn.Expression = "DateAdd(DateInterval.Day, 2, DateColumn)"

The problem is when this is run an error of: "The expression contains undefined function call DateAdd()." is returned.