SQLDataReader無法讀取

Question

我正在嘗試創建一個警報系統，以檢查與葯物有關的過敏症與與患者有關的過敏症（請參見下圖）。

當我運行代碼時，似乎只是完全跳過了SQLDataReader，我對if（reader.HasRows）進行了檢查，它僅顯示讀取器中沒有行。 我要做的就是在閱讀器的最后顯示一個帶有所選過敏名稱的消息框。 我使用的是SQL Server 2014.任何幫助將不勝感激。

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

首先，您的SqlCommand容易受到sql注入攻擊-您應該始終使用SqlParameter，因為它有助於防止sql注入。 因此，您的SqlCommand應該看起來像：

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);

您可以傳遞參數：

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

而且，查詢中的以下語句是多余的

WHERE A.allergyID = PA.allergyID 

因為您在此字段上有INNER JOIN

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

因此您可以從查詢中刪除多余的語句

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)

我很確定您其余的代碼或多或少都可以。 請查看您的查詢是否返回任何行。 例如，您可以復制查詢並將@medID替換為comboBox中的值。