sql-server-2008 - ExecuteScalar：连接属性尚未初始化

Question

为了运行executeScalar，我在 Internet 上尝试了很多建议，但我得到了错误ExecuteScalar: Connection property has not been initialized。我的INSERT查询工作正常，问题出在executeScalar.

conn.Open();
SqlCommand cmd = new SqlCommand(
    "INSERT INTO Products (Product_Name,Product_BarCode,Product_CP,Product_SP,
                           Product_Countainer,Product_Pcs,Product_MFGDate,
                           Product_ExpiryDate,Product_Grade)
     Values ('" + Name.Text + "','" + BarCode.Text + "','" + CostP.Value + "','" + 
             SellingP.Value + "','" + Countainer.Value + "','" + Pcs.Value + "','" + 
             MfgDate.Value + "','" + ExpDate.Value + "','" + Grade.SelectedItem + "')", 
     conn);
cmd.ExecuteNonQuery();
conn.Close();

conn.Open();
cmd.Connection = conn;
cmd = new SqlCommand("SELECT SUM(Product_CP) FROM Products AS Amount");
Amount = (double)cmd.ExecuteScalar();
MessageBox.Show(Amount.ToString());
conn.Close();

Answer 1

cmd = new SqlCommand(...);

正如错误明确指出的那样，此命令没有连接。

Answer 2

如果您使用 DBCommand 而不是 SQLCommand，这将无法解决问题，因为 DBCommand 是一个抽象类并且无法实例化..

对我有用的解决方案是：我在必须使用的地方使用 command.executeScalar()：DbCommand.executeScalar (command) // 效果很好！

Answer 3

这cmd.Connection = conn;

应该在声明之后

cmd = new SqlCommand("SELECT SUM(Product_CP) FROM Products AS Amount");
cmd.Connection = conn;