我正在为一个叫做OTServer的游戏服务器编程一个数据库管理器,第二次使用executereader()时遇到了问题。代码如下:
private void button1_Click(object sender, EventArgs e)
{
Form1 f = new Form1();
MySqlConnection conn = new MySqlConnection();
conn.ConnectionString = "Server=" + f.GetText1().Text + ";Username=" + f.GetText2().Text + ";Pwd=" + f.GetText3().Text + ";Database=" + f.GetText4().Text + ";";
conn.Open();
MySqlCommand cmd = new MySqlCommand("SELECT * FROM `players` WHERE name = @Name", conn);
cmd.Parameters.AddWithValue("@Name", textBox1.Text);
MySqlDataReader Reader = cmd.ExecuteReader(CommandBehavior.SingleRow);
while (Reader.Read())
{
label7.Text = (string)Reader[1];
label7.Show();
label8.Text = Reader[5].ToString();
label8.Show();
if ((int)Reader[6] == 1)
{
label9.Text = "Sorcerer (1)";
}
if ((int)Reader[6] == 2)
{
label9.Text = "Druid (2)";
}
if ((int)Reader[6] == 3)
{
label9.Text = "Paladin (3)";
}
if ((int)Reader[6] == 4)
{
label9.Text = "Knight (4)";
}
if ((int)Reader[6] == 0)
{
label9.Text = "None (0)";
}
label9.Show();
if ((int)Reader[3] == 1)
{
label10.Text = "Player";
}
if ((int)Reader[3] == 2)
{
label10.Text = "Tutor";
}
if ((int)Reader[3] == 3)
{
label10.Text = "Senior Tutor";
}
if ((int)Reader[3] == 4)
{
label10.Text = "Gamemaster";
}
if ((int)Reader[3] == 5)
{
label10.Text = "Community Manager";
}
if ((int)Reader[3] == 6)
{
label10.Text = "God";
}
if ((int)Reader[3] < 1 || (int)Reader[3] > 6)
{
label10.Text = "Unknown";
}
label10.Show();
label13.Text = "Account: " + Reader[4].ToString();
label13.Show();
}
Reader.Close();
cmd = new MySqlCommand("SELECT * FROM accounts WHERE id = @Account_ID", conn);
cmd.Parameters.AddWithValue("@Account_ID", label13.Text);
Reader = cmd.ExecuteReader(CommandBehavior.SingleRow);
while (Reader.Read())
{
label11.Text = (string)Reader[0];
label11.Show();
}
Reader.Close();
}
最佳答案
建议的解决方案:尝试在using
周围放置一个DataReader
块,或在上面调用Dispose
:
using (DataReader Reader = cmd.ExecuteReader(CommandBehavior.SingleRow))
{
// ...do something with your data reader... then finish by:
Reader.Close();
} // <-- Reader.Dispose() called automatically at the end of using block.
// ...prepare second command...
// the same again for the second command:
using (DataReader Reader = cmd.ExecuteReader(CommandBehavior.SingleRow))
{
// ...
Reader.Close();
}
问题的假定原因:DB connection对象可能会执行一些内部记帐以跟踪数据读取器。我发现在类似的情况下,一次只允许一个
DataReader
。所以我认为你的代码的问题是,当你在执行第二个数据读取器时,你没有显式地将它写下来,所以连接对象认为第一个数据读取器仍然在使用。另外。。。为什么不简化此代码:
if ((int)Reader[6] == 1)
{
label9.Text = "Sorcerer (1)";
}
if ((int)Reader[6] == 2)
{
label9.Text = "Druid (2)";
}
...
对于
Close
语句?: int x = (int)(Reader[6]);
string label9Text = string.Empty;
switch (x)
{
case 1: label9Text = "Sorcerer (1)"; break;
case 2: label9Text = "Druid (2)"; break;
...
}
label9.Text = label9Text;
(这样你就省去了很多重复的打字。)