SQLDataReader not reading

Question

I am trying to make an alert system that checks a medications linked allergies with a patients linked allergies (see image below).

When I run the code it seems to just completely skip the SQLDataReader, I have performed checks on if(reader.HasRows) and it just shows there are no rows in the reader. All I want to do is show a message box with the selected allergy name at the end of the reader. I am using SQL Server 2014.Any help will be greatly appreciated.

private void button_addItem_Click(object sender, RoutedEventArgs e)
{
    if (!string.IsNullOrEmpty(comboBox_select_Item.Text.ToString()))
    {
        using (SqlConnection conn = new SqlConnection(connection))
        {
            try
            {
                SqlCommand sqlCmd2 = new SqlCommand("SELECT allergyName, allergyDescription FROM Allergies A INNER JOIN PatientAllergies PA ON A.allergyID = PA.allergyID WHERE A.allergyID = PA.allergyID AND PA.allergyID = (SELECT allergyID FROM Medication_Allergies MA WHERE MA.medID = " + comboBox_select_Item.SelectedValue.ToString() + ")", conn);
                conn.Open();
                SqlDataReader sqlReader = sqlCmd2.ExecuteReader();
                Allergies allergies = new Allergies();

                while (sqlReader.Read())
                {
                    allergies.allergyName = Convert.ToString(sqlReader["allergyName"]);
                    allergies.allergyDescription = Convert.ToString(sqlReader["allergyDescription"]);
                }

                MessageBox.Show(allergies.allergyName);
                sqlReader.Close();
                FillSalesItemGrid();
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.ToString(), ex.ToString());
            }
        }
    }
}

Answer 1

First of all your SqlCommand is vulnerable to sql injections attack - you should always use SqlParameter as it helps you to prevent sql injections. So your SqlCommand should looks like :

SqlCommand sqlCmd2 = new SqlCommand("SELECT allergyName, allergyDescription FROM Allergies A INNER JOIN PatientAllergies PA ON A.allergyID = PA.allergyID WHERE A.allergyID = PA.allergyID AND PA.allergyID = (SELECT allergyID FROM Medication_Allergies MA WHERE MA.medID = @medID)", conn);

and you can pass parameter:

  sqlCmd2.Parameters.AddWithValue("@medID",comboBox_select_Item.SelectedValue);

What is more, following statement in your query is redundant

WHERE A.allergyID = PA.allergyID 

because you have INNER JOIN on this field

FROM Allergies A INNER JOIN PatientAllergies PA ON A.allergyID = PA.allergyID 

so you can remove redundant statement from your query

SELECT allergyName, allergyDescription FROM Allergies A INNER JOIN PatientAllergies PA ON A.allergyID = PA.allergyID WHERE PA.allergyID = (SELECT allergyID FROM Medication_Allergies MA WHERE MA.medID = @medID)

I'm pretty sure that rest of your code is more or less fine. Please have a look if your query returns any rows. For example you can copy your query and replace @medID with value from your comboBox.