Question

我在同一个打开的Connection上设置很多命令时遇到问题，它总是说有一个与命令关联的DataReader必须关闭，虽然我关闭了它仍然给我同样的问题，这是我的代码：

 protected void Afficher_click(object sender, EventArgs e)
    {
        using (SqlConnection con = new SqlConnection(cs))
        {
            SqlCommand cmd = new SqlCommand("select * from Consommation where idAbonnement = @ab and periode between @d1 and @d2 ",con);
            cmd.Parameters.AddWithValue("@ab", DropDownList1.SelectedValue);
            cmd.Parameters.AddWithValue("d1", TextBox1.Text);
            cmd.Parameters.AddWithValue("d2", TextBox2.Text);
            con.Open();
            GridView1.DataSource = cmd.ExecuteReader();
            GridView1.DataBind();
            //cmd.ExecuteReader().Close();
            cmd = new SqlCommand("select SUM(Qte) from Consommation where idAbonnement =" + DropDownList1.SelectedValue, con);
            Label2.Text = cmd.ExecuteScalar().ToString();
            cmd = new SqlCommand("select AVG(Qte) from Consommation where idAbonnement =" + DropDownList1.SelectedValue, con);
            Label4.Text = cmd.ExecuteScalar().ToString();
        }

您能否向我解释一下究竟是什么问题以及如何解决？先谢谢。

Answer 1

您应该关闭SqlDataReader。在这种情况下，最好的方法是使用：

GridView1.DataSource = cmd.ExecuteReader(System.Data.CommandBehavior.CloseConnection);

或使用其他方法，例如使用SqlDataAdapter和DataTable：

string sql = "select * from Consommation " +
             "where idAbonnement = @ab " +
             "and periode between @d1 and @d2 ";
using (SqlConnection con = new SqlConnection(cs))
using (SqlDataAdapter da = new SqlDataAdapter(sql, con))
{
    con.Open();
    var cmd = da.SelectCommand;
    cmd.Parameters.AddWithValue("@ab", DropDownList1.SelectedValue);
    cmd.Parameters.AddWithValue("d1", TextBox1.Text);
    cmd.Parameters.AddWithValue("d2", TextBox2.Text);
    DataTable dataSource = new DataTable();
    da.Fill(dataSource);
    GridView1.DataSource = dataSource;
    GridView1.DataBind();

   using (var cmdSumQte = new SqlCommand(
        "select SUM(Qte) from Consommation where idAbonnement = @idAbonnement", con))
    {
        cmdSumQte.Parameters.Add("@idAbonnement", SqlDbType.Int).Value =
            int.Parse(DropDownList1.SelectedValue);
        Label2.Text = cmdSumQte.ExecuteScalar().ToString();
    }

    using(var cmdAvgQte = new SqlCommand(
            "select AVG(Qte) from Consommation where idAbonnement = @idAbonnement", con))
    {
        cmdAvgQte.Parameters.Add("@idAbonnement", SqlDbType.Int).Value =
            int.Parse(DropDownList1.SelectedValue);
        Label4.Text = cmdAvgQte.ExecuteScalar().ToString();
    }
}

请注意，我还使用了其他命令的参数，也使用了多个。在这种情况下，你可以避免粗心的错误。

Answer 2

尝试为第二个命令使用不同的名称：

 using (SqlConnection con = new SqlConnection(cs))
        {
            SqlCommand cmd = new SqlCommand("select * from Consommation where idAbonnement = @ab and periode between @d1 and @d2 ",con);
            cmd.Parameters.AddWithValue("@ab", DropDownList1.SelectedValue);
            cmd.Parameters.AddWithValue("d1", TextBox1.Text);
            cmd.Parameters.AddWithValue("d2", TextBox2.Text);
            con.Open();
            GridView1.DataSource = cmd.ExecuteReader();
            GridView1.DataBind();
            cmd.Dispose();
            SqlCommand cmd2 = new SqlCommand("select SUM(Qte) from Consommation where idAbonnement =" + DropDownList1.SelectedValue, con);
            Label2.Text = cmd2.ExecuteScalar().ToString();
            SqlCommand cmd3 = new SqlCommand("select AVG(Qte) from Consommation where idAbonnement =" + DropDownList1.SelectedValue, con);
            Label4.Text = cmd3.ExecuteScalar().ToString();
        }

此外，非常重要：使用参数，您接触SQL注入

Answer 3

protected void Afficher_click(object sender, EventArgs e)
    {
        using (SqlConnection con = new SqlConnection(cs))
        {
            SqlCommand cmd = new SqlCommand("select * from Consommation where idAbonnement = @ab and periode between @d1 and @d2 ",con);
            cmd.Parameters.AddWithValue("@ab", DropDownList1.SelectedValue);
            cmd.Parameters.AddWithValue("d1", TextBox1.Text);
            cmd.Parameters.AddWithValue("d2", TextBox2.Text);
            con.Open();
            GridView1.DataSource = cmd.ExecuteReader(System.Data.CommandBehavior.CloseConnection);
            GridView1.DataBind();
            cmd.Dispose();
            cmd = null;
            cmd = new SqlCommand("select SUM(Qte) from Consommation where idAbonnement =" + DropDownList1.SelectedValue, con);
            Label2.Text = cmd.ExecuteScalar().ToString();
            cmd = new SqlCommand("select AVG(Qte) from Consommation where idAbonnement =" + DropDownList1.SelectedValue, con);
            Label4.Text = cmd.ExecuteScalar().ToString();
        }

Answer 4

由于您使用的是多个结果集，因此需要添加以下语句

MultipleActiveResultSets = TRUE;

在你的连接字符串中。

例如，

服务器= myServerAddress;数据库= MYDATABASE; Trusted_Connection = TRUE; MultipleActiveResultSets = TRUE;

Answer 5

这是我尝试过的解决方案，根据此处的帖子工作完美：https://blogs.msdn.microsoft.com/spike/2009/08/20/there-is-already-an-open-datareader-associated-with-this-command-which-must-be-closed-first-explained/

            using (SqlDataReader rd = cmd.ExecuteReader())
            {
                GridView1.DataSource = rd;
                GridView1.DataBind();
            }

错误：已经有一个与此命令关联的打开DataReader，必须先关闭它

5 个答案: