Question

string connectionString = ConfigurationManager.AppSettings["AllRttpDBConnectionString"];
MySqlConnection connection = new MySqlConnection(connectionString);
MySqlCommand command = connection.CreateCommand();

command.CommandText = "Select * from test where ServiceName like 'T%' " ;

try
{
  connection.Open();
}
catch (Exception e)
{
  Console.WriteLine(e.ToString());
}

try
{
  MySqlDataReader reader;
  reader = command.ExecuteReader();

  while (reader.Read())
  {
    Player.Name = reader["Name"].ToString();
    Player.Number = Convert.ToInt32(reader["Number"].ToString());

    //push to list
    PlayerList.Add(Player);
  }

  connection.Close();
}
catch (Exception e)
{
  connection.Close();
  logger.Info(e.ToString());
}

上面是我用来从数据库中读取多行到列表的代码。但是，我的所有列表项都具有完全相同的数据（数据库的最后一行）。

我知道这可能是一个非常简单，愚蠢的错误，但我只是看不到它。

Answer 1

看起来您反复添加相同的对象，将值更改为从当前行读取的值。你需要使用：

Player player = new Player()
player.Name = reader["Name"].ToString(); 
player.Number = Convert.ToInt32(reader["Number"].ToString()); 

//push to list 
PlayerList.Add(player);

然后将其添加到集合中。

Answer 2

看起来您正在不断修改单个Player实例。

要修复它，请为每条记录创建一个新实例：

while (reader.Read())
{
    // I'm guessing about the type here
    Player player = new Player();
    player.Name = reader["Name"].ToString();
    player.Number = Convert.ToInt32(reader["Number"].ToString());

    //push to list
    PlayerList.Add(player);
}

Answer 3

所以发生的事情是，每次将其添加到列表中时，您都不会创建新的Player。

将项目添加到列表时，您的代码应如下所示。

PlayerClass NewPlayer = new PlayerClass;
NewPlayer.Name = reader["Name"].ToString();
NewPlayer.Number = Convert.ToInt32(reader["Number"].ToString());

//push to list
PlayerList.Add(NewPlayer);

Answer 4

我建议您稍微改进一下代码：

public IEnumerable<Player> GetPlayers()
{
    string connectionString = ConfigurationManager.AppSettings["AllRttpDBConnectionString"];
    using (var conn = new MySqlConnection(connectionString))
    using (var cmd = conn.CreateCommand())
    {
        conn.Open();
        cmd.CommandText = "SELECT Name, Number FROM test WHERE ServiceName LIKE 'T%';";
        using (var reader = cmd.ExecuteReader())
        {
            while (reader.Read())
            {
                yield return new Player 
                {
                    Name = reader.GetString(0),
                    Number = reader.GetInt32(1)
                };
            }
        }
    }
}

当你需要创建一个列表时：

List<Player> playersList = GetPlayers().ToList();

您还需要确保妥善处理所有可支配资源，如我的示例所示。

从数据库中读取多行 - 我哪里错了？

4 个答案: