Question

I have a table with an identity column whose value I would like to get after an INSERT. The following code, which does not use parameters, is working perfectly:

string query = "INSERT INTO aTable ([aColumn]) VALUES (42)";
SqlCommand command = new SqlCommand(query, connection);
command.ExecuteNonQuery();

query = "SELECT CAST(SCOPE_IDENTITY() AS bigint)";
command = new SqlCommand(query, connection);
object identity = command.ExecuteScalar();

If I change the INSERT part of the above code to use a parameterized query, ExecuteScalar() suddenly returns a System.DBNull value. This is how the parameterized query code looks like:

string query = "INSERT INTO aTable ([aColumn]) VALUES (@aColumn)";
SqlCommand command = new SqlCommand(query, connection);
command.Parameters.AddWithValue("@aColumn", 42);
command.ExecuteNonQuery();

I have tried to change the SCOPE_IDENTITY code so that it uses an output parameter and invokes ExecuteNonQuery(), but I still get a null value in the out parameter. I have also tried running the code against two different versions of SQL Server (2012 and 2008, both Express Edition), again with the same result.

Any ideas what I am doing wrong here?

Answer 1

Try combining your INSERT and SELECT into one statement

string query = "INSERT INTO aTable ([aColumn]) VALUES (@aColumn);SELECT CAST(SCOPE_IDENTITY() AS bigint)"; 
SqlCommand command = new SqlCommand(query, connection); 
command.Parameters.AddWithValue("@aColumn", 42); 
object identity = command.ExecuteScalar();