ado.net无法从我的数据库中读取

Question

This is a really noob-problem but im tearing my hair soon. I'm trying to read from my local database but it gives me nothing. Here is the code:

protected void readBtn2_Click(object sender, EventArgs e)
{
    string ConnString = "server=localhost; Trusted_Connection=yes; database=expreimentalDB";

    string SqlString  = ("SELECT * FROM tblCity WHERE city = '@city'");

    using (SqlConnection conn = new SqlConnection(ConnString))
    {
        using (SqlCommand cmd = new SqlCommand(SqlString, conn))
        {
            cmd.CommandType = CommandType.Text;
            cmd.Parameters.AddWithValue("city", cityTB.Text);

            conn.Open();
            using (SqlDataReader reader = cmd.ExecuteReader())
            {
                GridView1.DataSource = reader;
                GridView1.DataBind();
            }
        }
    }
}

The connectionstring should work (because if i rename the database part in the string it crashes).

The sql is working (tried it in sql manager)

reader (the SqlDataReader) is empty What is it I havnt tried out yet?

Answer 1

You need to remove the single quotes from around @city in your query so that it becomes

string SqlString  = "SELECT * FROM tblCity WHERE city = @city";

and then

cmd.Parameters.AddWithValue("city", cityTB.Text);

needs to be changed to

cmd.Parameters.AddWithValue("@city", cityTB.Text);

Answer 2

I'm not quite sure, but shouldn't you have to prefix the name of the parameter with the @-sign when adding it to your command? Like this:

cmd.Parameters.AddWithValue("@city", cityTB.Text);