c# Windows 窗体数据库问题

Question

我正在尝试根据组合框中的名称从他们的表中获取制造商、供应商、项目组 ID。意味着我根据组合框中的名称将 id 传递给变量，然后将该 id 传递给数据库。但是当我运行这个应用程序时，我得到制造商、供应商和项目组变量的相同结果。这是为什么？

之前还可以，现在不行了！我想不通！

using (SqlConnection con = new SqlConnection(CS))
{
    con.Open();

    SqlCommand cmd = new SqlCommand("SELECT Manufact_Id from Manufacturer Where Name=@Name1", con);
    cmd.Parameters.AddWithValue("@Name1", combomanufacture_Createitem.Text);

    int a = Convert.ToInt32(cmd.ExecuteScalar());

    SqlCommand cmd2 = new SqlCommand("SELECT Supplier_Id from Supplier Where Supplier_Name=@Name2", con);
    cmd.Parameters.AddWithValue("@Name2", combo_supplierCreateitem.Text);

    int b = Convert.ToInt32(cmd.ExecuteScalar());

    SqlCommand cmd3 = new SqlCommand("SELECT ItemGroup_Id from ItemGroup Where Name=@Name3", con);
    cmd.Parameters.AddWithValue("@Name3", combo_itemgroupCreateitem.Text);

    int c = Convert.ToInt32(cmd.ExecuteScalar());

    try
    {
        SqlCommand cmd1 = new SqlCommand("INSERT INTO Items (Custom_Code, Name, Manufacturer, Supplier, Item_Group, Activate, Purchase_Rate, Landing_Cost, Profit_Percentage, Price_to_Customer, MRP,Opening_Stock, Manage_Stock, Description, Discount)  VALUES (@Customcode, @Name, @Manufacturer, @Supplier, @Itemgroup, @Activate, @Purchasedate, @Landingcost, @Profitpercentage, @PricetoCustomer, @MRP, @Openingstock, @Managestock, @Description1, @Discount)", con);

        cmd1.Parameters.AddWithValue("@Customcode", txt_customcode_Createitem.Text);
        cmd1.Parameters.AddWithValue("@Name", txt_nameCreateitem.Text);
        cmd1.Parameters.AddWithValue("@Manufacturer", a);
        cmd1.Parameters.AddWithValue("@Supplier", b);
        cmd1.Parameters.AddWithValue("@Itemgroup", c);
        cmd1.Parameters.AddWithValue("@Activate", combo_activateCreateitem.Text);
        cmd1.Parameters.AddWithValue("@Purchasedate", txt_purchasedateCreateitem.Text);
        cmd1.Parameters.AddWithValue("@Landingcost", txt_landingcosCreateitem.Text);
        cmd1.Parameters.AddWithValue("@Profitpercentage", txt_activateCreateitem.Text);
        cmd1.Parameters.AddWithValue("@PricetoCustomer", txt_PricetocustCreateitem.Text);
        cmd1.Parameters.AddWithValue("@MRP", txt_mrpCreateitem.Text);
        cmd1.Parameters.AddWithValue("@Openingstock", txt_openingstockCreateitem.Text);
        cmd1.Parameters.AddWithValue("@Managestock", combomanagestock_Createitem.Text);
        cmd1.Parameters.AddWithValue("@Description1", txt_descriptionCreateitem.Text);
        cmd1.Parameters.AddWithValue("@Discount", txt_DiscountCreateitem.Text);

        cmd1.ExecuteReader();

        MessageBox.Show("Items added Successfully");

        con.Close();
    }
    catch (Exception e1)
    {
        MessageBox.Show(e1 + "Please enter valid data");
    }
}

Answer 1

您正在创建新命令 (cmd2/cmd3) 但您设置了参数并执行旧实例.. (cmd)

所以你正在执行相同的 cmd，这就是你得到相同结果的原因：

SqlCommand cmd = new SqlCommand("SELECT Manufact_Id from Manufacturer Where Name=@Name1", con);
cmd.Parameters.AddWithValue("@Name1", combomanufacture_Createitem.Text);
int a = Convert.ToInt32(cmd.ExecuteScalar());

SqlCommand cmd2 = new SqlCommand("SELECT Supplier_Id from Supplier Where Supplier_Name=@Name2", con);
// HERE!!  cmd.Parameters... should be cmd2.Parameters
cmd.Parameters.AddWithValue("@Name2", combo_supplierCreateitem.Text);
int b = Convert.ToInt32(cmd.ExecuteScalar());

SqlCommand cmd3 = new SqlCommand("SELECT ItemGroup_Id from ItemGroup Where Name=@Name3", con);
// AND HERE  cmd.Parameters... should be cmd3
cmd.Parameters.AddWithValue("@Name3", combo_itemgroupCreateitem.Text);
// cmd.execute?  should be cmd3....
int c = Convert.ToInt32(cmd.ExecuteScalar());

复制/粘贴错误..

Answer 2

您正在为第二个和第三个命令执行第一个“cmd”。

SqlCommand cmd = new SqlCommand("SELECT Manufact_Id from Manufacturer Where Name=@Name1", con);
            cmd.Parameters.AddWithValue("@Name1", combomanufacture_Createitem.Text);
            int a = Convert.ToInt32(cmd.ExecuteScalar());

            SqlCommand cmd2 = new SqlCommand("SELECT Supplier_Id from Supplier Where Supplier_Name=@Name2", con);
            cmd.Parameters.AddWithValue("@Name2", combo_supplierCreateitem.Text);
            int b = Convert.ToInt32(cmd.ExecuteScalar());

            SqlCommand cmd3 = new SqlCommand("SELECT ItemGroup_Id from ItemGroup Where Name=@Name3", con);
            cmd.Parameters.AddWithValue("@Name3", combo_itemgroupCreateitem.Text);
            int c = Convert.ToInt32(cmd.ExecuteScalar());

应该是：

SqlCommand cmd = new SqlCommand("SELECT Manufact_Id from Manufacturer Where Name=@Name1", con);
            cmd.Parameters.AddWithValue("@Name1", combomanufacture_Createitem.Text);
            int a = Convert.ToInt32(cmd.ExecuteScalar());

            SqlCommand cmd2 = new SqlCommand("SELECT Supplier_Id from Supplier Where Supplier_Name=@Name2", con);
            cmd2.Parameters.AddWithValue("@Name2", combo_supplierCreateitem.Text); //UPDATED!
            int b = Convert.ToInt32(cmd2.ExecuteScalar()); //UPDATED!

            SqlCommand cmd3 = new SqlCommand("SELECT ItemGroup_Id from ItemGroup Where Name=@Name3", con);
            cmd3.Parameters.AddWithValue("@Name3", combo_itemgroupCreateitem.Text); //UPDATED!
            int c = Convert.ToInt32(cmd3.ExecuteScalar()); //UPDATED!

您可能复制/粘贴并忘记将 2 和 3 添加到 cmd 的末尾！