如何修复ExecuteReader错误

本文关键字：错误 ExecuteReader 何修复 | 更新日期: 2023-09-27 18:05:55

Error异常类型为" System.Data.SqlClient. sql "。在System.Data.dll中发生了SqlException'，但未在用户代码中处理。如何解决这个问题?图片:https://i.stack.imgur.com/7Sibc.png 

    private void Form1_Load(object sender, EventArgs e)
    {
        SqlConnection conn = new SqlConnection(@"Data Source=QEAG1YU4664IBKF'HUYNHBAO;Initial Catalog=TonghopDB;User ID=sa;Password=koolkool7");
        conn.Open();
        SqlCommand sc = new SqlCommand("select Title from TongHopDB", conn);
        SqlDataReader reader;
        reader = sc.ExecuteReader();
        DataTable dt = new DataTable();
        dt.Columns.Add("Title", typeof(string));
        dt.Load(reader);
        cboxDB.ValueMember = "Title";
        cboxDB.DisplayMember = "Title";
        cboxDB.DataSource = dt;
        conn.Close();
    }
    private void cboxDB_SelectedIndexChanged(object sender, EventArgs e)
    {
        string sql = "Select Title, Post from TongHopDB where Title = " + cboxDB.SelectedValue.ToString(); // câu query có thể khác với kiểu dữ liệu trong database của bạn
        SqlConnection conn = new SqlConnection(@"Data Source=QEAG1YU4664IBKF'HUYNHBAO;Initial Catalog=TonghopDB;User ID=sa;Password=koolkool7");
        conn.Open();
        SqlCommand cmd = new SqlCommand(sql, conn);
        SqlDataReader sdr = cmd.ExecuteReader();
        textBox1.Text = sdr.GetValue(0).ToString();
        textBox2.Text = sdr.GetValue(1).ToString();
        sdr.Close();
        sdr.Dispose();
        conn.Close();
        conn.Dispose();
    }

如何修复ExecuteReader错误

 string sql = "Select Title, Post from TongHopDB where Title = '" + cboxDB.SelectedValue.ToString()+"'";

但是我强烈建议使用参数:

 string sql = "Select Title, Post from TongHopDB where Title = @Title";
cmd.Paramaters.Add( "@Title",cboxDB.SelectedValue.ToString());

我强烈怀疑你的Title是字符类型的，这就是为什么它需要用单引号作为;

where Title = '" + cboxDB.SelectedValue.ToString() + "'";

但不要这样用。

您应该始终使用参数化查询。这种字符串连接容易受到SQL注入攻击。

还可以使用using语句自动处理SqlConnection, SqlCommand和SqlDataReader对象，而不是手动调用Close或Dispose方法。

using(var conn = new SqlConnection(@"Data Source=QEAG1YU4664IBKF'HUYNHBAO;Initial Catalog=TonghopDB;User ID=sa;Password=koolkool7"))
using(var cmd = conn.CreateCommand())
{
   cmd.CommandText = "Select Title, Post from TongHopDB where Title = @title";
   cmd.Parameters.Add("@title", SqlDbType.NVarChar).Value = cboxDB.SelectedValue.ToString();
   // I assumed your column type is nvarchar.
   conn.Open();
   using(SqlDataReader sdr = cmd.ExecuteReader())
   {
      if(dr.Read())
      {
         textBox1.Text = sdr.GetValue(0).ToString();
         textBox2.Text = sdr.GetValue(1).ToString();
      }
   }
}

cboxDB。根据屏幕截图中显示的错误，SelectedValue是Apple。你的SQL语句用简单的英语说:

选择标题(列)等于Apple(列)的TongHopDB(表)中的Title(列)和Post(列)

Apple不是一个有效的列!

虽然可以简单地在cboxDB的值周围添加单引号，但您应该使用参数而不是连接字符串。http://blog.codinghorror.com/give-me-parameterized-sql-or-give-me-death/

相关文章：