Update field by code behind

Question

I have an existing list with a text field and records in it. Now I want to change that text field into a calculated field to make it concat two other text fields in the list (possibly by changing the schema related to that field thru code behind). I've tried doing..

fieldThree.Type = SPFieldType.Calculated;
myList.Update();
SPFieldCalculated calcField = (SPFieldCalculated)fieldThree;
calcField.Formula = @"=CONCATENATE([fieldOne],"" "",[fieldTwo])";
calcField.Update();

As it seems.. I can't explicitly convert a text field to a calculated one.

Answer 1

As you've found, you can't convert a text field into a calculated one. What you'll have to do is add the calculated field as a new column.

If you want to do this through code you'll need to use the SPList.Fields.Add() method.