使用列名称的变量选择查询返回的列。 （asp.net C＃）

Question

I have searched for most of the day and I believe I may just be not able to explain myself to a search engine. Please forgive me on this. I have one drop down list I use to get the column names with the code below.

MySQLDataSource.ConnectionString = matt.GetConnectionString();
MySQLDataSource.SelectCommand = "SELECT name FROM sys.syscolumns WHERE (id = 
      (SELECT id    FROM sys.sysobjects WHERE (name = 'tbl_EquipmentStock')))";
DropDownList1.DataValueField = "name";
DropDownList1.DataTextField = "name";

Now, the intention of my work is to use the selected item from this to create the sqldatasource of the next drop down.

   protected void DropDownList1_SelectedIndexChanged(object sender, EventArgs e)
{
    funtions matt = new funtions(); // funtions is the class that contains my connection string.
    string frank = DropDownList1.SelectedValue;
    a_c_instruction.Text = " Data filtered on: ";
    selectedItem.Text = frank;
    string sql = "SELECT " + frank + " FROM tbl_EquipmentStock"; 
    AnotherSqlDataSource.ConnectionString = matt.GetConnectionString();
    AnotherSqlDataSource.SelectCommand = sql;
    DropDownList2.DataValueField = frank;
    DropDownList2.DataTextField = frank;
    DropDownList2.Visible = true;
}

However, when I attempt to get this to work, the DropDownList2 doesn't populate. What could i be missing? Thank you for looking at my problem.

Answer 1

I tested your code and it works on my machine. I'm guessing that, in order for this to happen right after the column is selected, you need to make sure that the AutoPostBack option on DropDownList1 is set to true .