Question

I have this below code to retrieve data from db and when I run the Code Analysis from Visual Studio, it suggests me to call dispose method on SqlConnection, DataTable and SqlDataAdapter objects.

        SqlConnection sqlconn = new SqlConnection(ConfigurationManager.ConnectionStrings["connstr"].ConnectionString);
        SqlCommand cmd = sqlconn.CreateCommand();
        cmd.CommandText = "SELECT * FROM tbl_serial WHERE serial = @serial";
        cmd.Parameters.AddWithValue("@serial", txtQuery.Text);
        DataTable dt = new DataTable();
        SqlDataAdapter da = new SqlDataAdapter();
        try
        {
            sqlconn.Open();
            da.SelectCommand = cmd;
            da.Fill(dt);

        }
        catch (SqlException ex)
        {
            lblStatus.Text = ex.Message;
        }
        finally
        {
            sqlconn.Close();
        }

        if (dt.Rows.Count > 0)
        {
            lblStatus.Text = "FOUND!";
        }
        else
        {
            lblStatus.Text = "NOT FOUND!";
        }

And this is my first time doing this, I called dispose method on sqlconn just like this –

        finally
        {
            sqlconn.Close();
            sqlconn.Dispose();
        }

But then, Visual Studio warns me like this –

CA2202 : Microsoft.Usage : Object ‘sqlconn’ can be disposed more than
once in method ‘test_search.Unnamed1_Click(object, EventArgs)’. To
avoid generating a System.ObjectDisposedException you should not call
Dispose more than one time on an object.: Lines: 41

So I would like to know when should I correctly call dispose methods.

Answer 1

Here is your code re-written without ever having to all Dispose/Close manually

using (var sqlconn = new SqlConnection(ConfigurationManager.ConnectionStrings["connstr"].ConnectionString))
using (var cmd = sqlconn.CreateCommand())
{
    cmd.CommandText = "SELECT * FROM tbl_serial WHERE serial = @serial";
    cmd.Parameters.AddWithValue("@serial", txtQuery.Text);
    using (var dt = new DataTable())
    using (var da = new SqlDataAdapter())
    {
        try
        {
            sqlconn.Open();
            da.SelectCommand = cmd;
            da.Fill(dt);

        }
        catch (SqlException ex)
        {
            lblStatus.Text = ex.Message;
        }

        lblStatus.Text = dt.Rows.Count > 0 ? "FOUND!" : "NOT FOUND!";
    } 
}