Defining Column Value Calculations

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Calculation expression

Similar to constraint expressions (see Row and Column Level Constraints for more information), calculation expressions defined through the C1ViewColumn.CalculationExpression property are treated as the code of some class method. It returns a value of a type appropriate to a column data type and it is expressed in a specified .NET Framework programming language. Such a class has the following members which can be used in the calculation:

Members	Description
row	References a row on which column calculation is performed. If the expression is defined for a C1DataView the data type is C1ViewRow. If the expression is defined for a DataColumn the data type is type System.Data.DataRow.
column	References a column on which the value is calculated. If the expression is defined for a C1ViewColumn the data type is C1ViewColumn. If the expression is defined for a DataColumn in DataSetExtender the data type is System.Data.DataColumn.
baseValue	Contains the value before the calculation is applied which is the base value of a column.

Column value transformation process

In general, when a C1ViewColumn value in a certain C1ViewRow is being retrieved, the following chain of column value transformations occurs:

If C1ViewColumn represents a certain DataColumn:
1. A value of base DataColumn is retrieved.
2. A calculation expression (defined in the DataColumnExtender.CalculationExpression property) of the corresponding DataColumnExtender of DataSetExtender is evaluated. The value of the baseValue property accessible from this expression is set to the value produced in step 1.
If C1ViewColumn is calculated (that is, defined through expression in the View Definition statement):
1. A value of C1ViewColumn is calculated according its expression definition.

In any case:
1. A calculation expression defined in the CalculationExpression property of C1ViewColumn is evaluated. The baseValue property accessible from this expression is set to a value produced either in step 2 or step 3 (depending on the kind of C1ViewColumn).
2. If the RaiseCalculateColumnEvents property value is set to True then the CalculateColumn event is triggered. The value of event arguments Value property is set to a value produced in step 4; this property value can be changed in the event handler code and it becomes a value of the C1ViewColumn.

Note: A calculated column value is not stored in the base DataRow, the calculation is just a function on a base value stored in the row.