Chapter 13 Connector/Net FAQ

Questions

Questions and Answers

13.1: How do I obtain the value of an auto-incremented column?

When using CommandBuilder, setting ReturnGeneratedIdentifiers property to true no longer works, as CommandBuilder does not add last_insert_id() by default.

CommandBuilder hooks up to the DataAdapter.RowUpdating event handler, which means it will get called for every row. It examines the command object and, if it is the same referenced object, it essentially rebuilds the object, thereby destroying your command text changes.

One approach to solving this problem is to clone the command object so you have a different actual reference:

dataAdapter.InsertCommand = cb.GetInsertCommand().Clone()

This will work, but since the CommandBuilder is still connected to the DataAdapter, the RowUpdating event will still fire and performance will be hit. To stop that, once all your commands have been added you need to disconnect the CommandBuilder from the DataAdapter:

cb.DataAdapter = null;

The last requirement is to make sure the id that is returned by last_insert_id() has the correct name. For example:

SELECT last_insert_id() AS id

A complete working example is shown here:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

using System.Data;
using MySql.Data;
using MySql.Data.MySqlClient;

namespace GetAutoIncId
{
    class Program
    {
        static void Main(string[] args)
        {
            string connStr = "server=localhost;user=root;database=TestDB;port=3306;password=******;";
            MySqlConnection conn = new MySqlConnection(connStr);

            try
            {
                Console.WriteLine("Connecting to MySQL...");
                conn.Open();

                string sql = "SELECT * FROM TestTable";

                MySqlDataAdapter da = new MySqlDataAdapter(sql, conn);
                MySqlCommandBuilder cb = new MySqlCommandBuilder(da);

                MySqlCommand cmd = new MySqlCommand();
                cmd.Connection = conn;
                cmd.CommandText = sql;
                // use Cloned object to avoid .NET rebuilding the object, and 
                // thereby throwing away our command text additions.
                MySqlCommand insertCmd = cb.GetInsertCommand().Clone(); 
                insertCmd.CommandText = insertCmd.CommandText + ";SELECT last_insert_id() AS id";
                insertCmd.UpdatedRowSource = UpdateRowSource.FirstReturnedRecord;
                da.InsertCommand = insertCmd;
                cb.DataAdapter = null; // Unhook RowUpdating event handler

                DataTable dt = new DataTable();
                da.Fill(dt);

                DataRow row = dt.NewRow();
                row["name"] = "Joe Smith";

                dt.Rows.Add(row);
                da.Update(dt);

                System.Console.WriteLine("ID after update: " + row["id"]);
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex.ToString());
            }

            conn.Close();
            Console.WriteLine("Done.");
        }
    }
}