Question

I have a table that has an Identity column and another column needs to have its value based on the computed identity column.

My EF code looks like this:

var context = new DBEntities();
var newTableRow = new TableRow();
newTableRow.Column1 = newTableRow.ComputedColumn;
context.TableRows.Add(newTableRow);
context.SaveChanges();

If ComputedColumn is an IDENTITY and Column1 is a nullable varchar(50) I would expect the value of Column1 to be the same as the ComputedColumn but it is null.
I have even tried this:

var context = new DBEntities();
var newTableRow = new TableRow();
context.TableRows.Add(newTableRow);
context.SaveChanges();
newTableRow.Column1 = newTableRow.ComputedColumn;
context.SaveChanges();

AND

var context = new DBEntities();
var newTableRow = new TableRow();
context.TableRows.Add(newTableRow);
context.SaveChanges();
var getTableRow = context.TableRows.Single(r => r.ComputedColumn == newTableRow.ComputedColumn);
getTableRow.Column1 = newTableRow.ComputedColumn.ToString();
context.SaveChanges();

Keep in mind that this is part of a larger transaction. What I don’t want to do is complete the transaction then in a separate transaction do another update. I would like to keep everything in one transaction. This had been working in an insert proc before.

Thanks,

Brett

Answer 1

Your second an third example should work if ComputedColumn has DatabaseGeneratedOption.Identity. But they have separate transactions, which you don’t want.

Your first example can’t work. When a column has DatabaseGeneratedOption.Identity, EF reads the identity value back when executing SaveChanges. It is not aware of any special instruction you might have tried to convey with

newTableRow.Column1 = newTableRow.ComputedColumn;

As for EF, it’s just an assignment with an empty value.

Maybe the best alternative is to add a computed column to your database table. You will kill two birds with one stone:

• It is transactional, because the computed column just re-displays the identity column
• You prevent redundancy and possible value conflicts.