C＃SQL查询不返回任何内容

Question

I am trying to get my Winforms app to query a SQL Server CE database and return all rows that correspond to the column name specified by the user through a drop down list. When I run the programs it will return just a blank dataGrid. This is my first time working with SQL Server CE so any help would be appreciated.

My code is:

private void srchBTN_Click(object sender, EventArgs e)
{
   string conString = Properties.Settings.Default.CurricularChangeTrackerConnectionString;

   using (SqlCeConnection conn = new SqlCeConnection(conString))
   {
       string queryString = ("SELECT * FROM SecondaryEducation WHERE ProgramCode='" + PrgmCde.SelectedValue + "'");

       try
       {
          conn.Open();

          using (SqlCeDataAdapter adapter = new SqlCeDataAdapter(queryString, conn))
          {
              DataTable table = new DataTable();
              adapter.Fill(table);

              dataGridView1.DataSource = table;
              adapter.Dispose();
          }

          conn.Close();
       }
       catch (Exception ex)
       {
           MessageBox.Show(ex.Message);
       }
   }
}

Answer 1

You are declaring the data table inside the using statement, try this

private void srchBTN_Click(object sender, EventArgs e)
{
   string conString = Properties.Settings.Default.CurricularChangeTrackerConnectionString;
   DataTable table = new DataTable();
   using (SqlCeConnection conn = new SqlCeConnection(conString))
   {
     string queryString = ("SELECT * FROM SecondaryEducation WHERE ProgramCode='" + PrgmCde.SelectedValue + "'");

   try
   {
      conn.Open();

      using (SqlCeDataAdapter adapter = new SqlCeDataAdapter(queryString, conn))
      {

          adapter.Fill(table);
          dataGridView1.DataSource = table;
          adapter.Dispose();
      }

      conn.Close();
   }
   catch (Exception ex)
   {
       MessageBox.Show(ex.Message);
   }
  }
}

That way the table wont be disposed of when the scope of the using statement is ended.

Answer 2

If a property is not specified in ValueMember, SelectedValue returns the results of the ToString method of the object.

My point is you may not be getting what you think from the comboBox.

Try this:

string queryString = ("SELECT * FROM SecondaryEducation WHERE ProgramCode='" + PrgmCde.Items[PrgmCde.SelectedIndex].ToString() + "'");