Cannot remove this column, because it is part of an expression: in C#

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I have dataable and iam masking one column by adding new column name as MASKEDSSN.
It has been masked. But i need to Remove Old Column name SSN. While Removing it throws an error as

Quote:
Quote:
Cannot remove this column, because it is part of an expression: MaskedSSN = 'XXX-XX-'+SUBSTRING(CONVERT(SSN, System.String),6,4).

DataTable employeeTable = new DataTable();
employeeTable.Rows.Add("123455789");
employeeTable.Rows.Add("123447789");
employeeTable.Rows.Add("823456719");
employeeTable.Columns.Add("SSN");

Below is the code i have tried

int index = employeeTable.Columns["SSN"].Ordinal;
               employeeTable.Columns.Add("MaskedSSN", typeof(string));
               employeeTable.Columns["MaskedSSN"].Expression = "'XXX-XX-'+SUBSTRING(CONVERT(SSN, System.String),6,4)";
               DataTable newsss = new DataTable();

               newsss = employeeTable.Copy();
               newsss.AcceptChanges();
               newsss.Columns.RemoveAt(index);
               newsss.Columns.Remove("SSN");

What I have tried:

<pre> int index = employeeTable.Columns["SSN"].Ordinal;
                employeeTable.Columns.Add("MaskedSSN", typeof(string));
                employeeTable.Columns["MaskedSSN"].Expression = "'XXX-XX-'+SUBSTRING(CONVERT(SSN, System.String),6,4)";
                DataTable newsss = new DataTable();

                newsss = employeeTable.Copy();
                newsss.AcceptChanges();
                newsss.Columns.RemoveAt(index);
                newsss.Columns.Remove("SSN");

Posted 20-Dec-18 20:54pm

Vinodh Muthusamy

Updated 20-Dec-18 21:17pm

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OriginalGriff · Accepted Answer · 2018-12-20T21:18:00

Solution 1

Well yes. What did you expect?
You create MASKEDSSN and set it's value to be a computed column based on SSN. Computer columns aren't "evaluate once and forget", they are evaluated when the value is needed: when a row is added, when a row is displayed. If you could remove the SSN column, the MASKEDSSN column would be unable to compute the value of rows!

So very understandably, the system complains and tells you "You can't do that".

Posted 20-Dec-18 21:18pm

OriginalGriff

Comments

Vinodh Muthusamy 21-Dec-18 3:26am

Is there any other way to mask, without adding new columns

Richard Deeming 21-Dec-18 10:57am

Loop through the rows and update the column value to the masked value.