Reverse of Calculated Field

[egsuh]

Is there a way that I can reverse the operation of calculated field?  To explain more detail, I'd like to save several options in a blob field in the form of name=value pair string (ie. StringList.Text). Let's say that there are three options for each record.

   min=1
   max=100
   step=5


I'd like to edit this one by one. Separation is simple. AStringList.Text:= db.fieldbyname('option').AsString; , and then AStringList.Values['min'] etc. will do.

And I can edit them using TEdit, etc. and save back at beforepost or beforescroll event handler of dataset.

As another way, I may make three calculated fields in the Lazarus dataset objects, and calculate the values at OnCalcField event handler. But calculated fields are read-only, I think.
Are there any way to change original field data through calculated field, or other thing?