How to Add Expression Fields

27 Mar 20181 minute to read

To add an expression field to the data in the Grouping Engine, you must first create an instance of an ExpressionFieldDescriptor and add it to the ExpressionFields collection in the TableDescriptor. The ExpressionFieldDescriptor will allow you to specify a string that holds an algebraic expression using any of the other fields that are in the record.

The following code snippet illustrates this.

C#

// Add an expression property that multiplies field B by 2.1 and adds 3.2
ExpressionFieldDescriptor expressionFieldDescriptor = new ExpressionFieldDescriptor("MultipleOfB", "2.1 * [B] + 3.2");
this.groupingEngine.TableDescriptor.ExpressionFields.Add(expressionFieldDescriptor);
 
// Assumes the datasource to be an IList, holding objects of type MyObject.
MyObject o = this.groupingEngine.Table.Records[2].GetData() as MyObject;
       
// MultipleOfB is an expression field name and B is a property in MyObject.
object someValue = this.groupingEngine.Table.Records[2].GetValue("B");
object someExpressionValue = this.groupingEngine.Table.Records[2].GetValue("MultipleOfB");

VB

' Add an expression property that multiplies field B by 2.1 and adds 3.2
Dim expressionFieldDescriptor As New ExpressionFieldDescriptor("MultipleOfB", "2.1 * [B] + 3.2")
Me.groupingEngine.TableDescriptor.ExpressionFields.Add(expressionFieldDescriptor)
 
' Assumes the datasource to be an IList, holding objects of type MyObject.
Dim o As MyObject = CType(Me.groupingEngine.Table.Records(2).GetData(), MyObject)
 
' MultipleOfB is an expression field name and B is a Property in MyObject.
Dim someValue As Object = Me.groupingEngine.Table.Records(2).GetValue("B")
Dim someExpressionValue As Object = Me.groupingEngine.Table.Records(2).GetValue("MultipleOfB")