Question

我是Programming and C＃的新手，尤其是我正在尝试创建一个连接到sql server的小应用程序，它可以让我保存客户名称，电话和地址。我面临的一个问题就是我的“检查数据是否已经存在”总是告诉它它不是空的而且无法保存。我很感激一些帮助。我知道这是非常的菜鸟，很抱歉打扰。

      //Create and Open Connection
        SqlConnection con = new SqlConnection("Data Source=KDC-LP\\SQLEXPRESS;Initial Catalog=ClientsDB;Integrated Security=True");
        SqlDataReader reader = null;
        con.Open();

        //Finding if data already exists
        SqlCommand cmd = new SqlCommand("select name from clients where name = @name or phone1 in (@phone1, @phone2, @phone3) ", con);
        cmd.Parameters.AddWithValue("@name", textbox1.Text);
        cmd.Parameters.AddWithValue("@phone1", textbox2.Text);
        cmd.Parameters.AddWithValue("@phone2", textbox3.Text);
        cmd.Parameters.AddWithValue("@phone3", textbox4.Text);            
        reader = cmd.ExecuteReader();

        //Saving or not ?
        MessageBoxResult msg = MessageBox.Show("Are you sure you want to save the new data", " Save", MessageBoxButton.YesNo, MessageBoxImage.Question);
        switch (msg)
        {
            case MessageBoxResult.Yes:

                if (reader != null) //Name, Phones already exists
                {
                    reader.Close();
                    MessageBoxResult notsaved = MessageBox.Show("Data already exists please check", "Save", MessageBoxButton.OK, MessageBoxImage.Warning);
                }
                else
                {
                    //Saving
                    reader.Close();
                    SqlCommand cmdins = new SqlCommand("INSERT INTO Clients (name,phone1,phone2,phone3,address) Values ('" + textbox1.Text + "', '" + textbox2.Text + "', '" + textbox3.Text + "', '" + textbox4.Text + "', '" + textbox5.Text + "')", con);
                    cmdins.ExecuteNonQuery();
                    textbox1.Clear();
                    textbox2.Clear();
                    textbox3.Clear();
                    textbox4.Clear();
                    textbox5.Clear();
                    MessageBoxResult saved = MessageBox.Show("Data is Saved", "Save", MessageBoxButton.OK, MessageBoxImage.Information);
                }
                break;

                //Not Saving
            case MessageBoxResult.No:
                {
                    MessageBoxResult msgno = MessageBox.Show("Data is not saved", "Save", MessageBoxButton.OK, MessageBoxImage.Warning);
                }
                break;
        }

        //Closing Connection 
        con.Close();

Answer 1

HasRows属性告诉您查询是否返回了行，您需要使用：

            if (reader.HasRows) //Name, Phones already exists
            {
                reader.Close();
                MessageBoxResult notsaved = MessageBox.Show("Data already exists please check", "Save", MessageBoxButton.OK, MessageBoxImage.Warning);
            }

Answer 2

ExecuteReader总是会让读者回复。如果查询未找到任何数据，则仍会返回读者。它只是不“包含”任何数据。这就是您需要检查的内容：

if (reader.HasRows) //Name, Phones already exists

c＃ - 查询永远不会为空？

2 个答案: