Question

I have a query – “SELECT PK1 FROM users“;

I also have a datatable named myTable with three fields of type int;

-----------
| myTable |
-----------
| field1  |
| field2  |
| field3  |
-----------

For each row returned from my query, I would like to put the PK1 value into field2 in myTable leaving field1 and field3 null.

Here’s some sample code I have tried so far, but it doesn’t seem to be working. Instead, the field PK1 is appended to the end of myTable as a new field.

class Program
    {
        static void Main(string[] args)
        {
            string SQL = "SELECT PK1 FROM users";
            SqlConnection connection = new SqlConnection([my connection string]);
            DataTable myTable = new DataTable();
            SqlDataAdapter adapter = new SqlDataAdapter();

            adapter.SelectCommand = new SqlCommand(SQL, connection);
            myTable.Columns.Add("field1", typeof(Int32));
            myTable.Columns.Add("field2", typeof(Int32));
            myTable.Columns.Add("field3", typeof(Int32));
            DataTableMapping dataMapping = adapter.TableMappings.Add("myTable", "users");
            dataMapping.ColumnMappings.Add("PK1", "field2");

            adapter.Fill(myTable);

            foreach (DataRow row in myTable.Rows)
            {
                Console.WriteLine("------------");
                foreach (DataColumn column in myTable.Columns)
                {
                    Console.WriteLine(column.ColumnName + " : " + row[column]);
                }
            }


            Console.ReadKey();
        }
    }

Is there an issue in my code, or is there another way I can map the fields across?

This is a simplified example for the purposes of this question, as such mapping the field names would be ideal rather than inserting the value at a given position.

Answer 1

I think if it is your requirement then there is nothing wrong with this approach.
Change your query to the following, and you don’t need the mapping.

string SQL = "SELECT PK1 as field2 FROM users";