多个datagridview数据更新到数据库mysql - vb.net

Question

我创建了一个具有两个不同界面的购物系统。 管理界面用于向数据库添加/更新/删除项目，客户界面用于购买产品。 用户购买产品后，我在管理界面中更新数量时遇到问题。 管理界面中的数量会更新，直到值变为负数。

Try
    For Each row As DataGridViewRow In formPOS.ProductAddToCartDGV.Rows
        dbconnection()
        sql = "UPDATE products_database SET Product_Quantity = Product_Quantity - @ProductQuantity WHERE Product_Code = @ProductCode;"
        cmd = New MySqlCommand
        With cmd
            .Connection = conn
            .CommandText = sql
            .Parameters.Clear()
            .Parameters.AddWithValue("@ProductCode", row.Cells(0).Value)
            .Parameters.AddWithValue("@ProductQuantity", row.Cells(3).Value)
            result = .ExecuteNonQuery()

            If result = 0 Then
                MsgBox("Error in updating stocks")
            Else
                MsgBox("Successfully update stocks")
            End If
        End With
    Next
Catch ex As Exception
    MsgBox(ex.Message)
Finally
    conn.Close()
End Try

Answer 1

是否要确保客户输入的值小于或等于剩余总数？ 如果是这样，您可以在WHERE子句中添加条件Product_Quantity >= CAST(@ProductQuantity AS int) 。

For i As Integer = 0 To CustomerDGV.Rows.Count - 2
    Dim constr As String = "connection string"
    Dim sql As String = "UPDATE products_database SET Product_Quantity = Product_Quantity - @ProductQuantity WHERE Product_Code = CAST(@ProductCode AS int) AND Product_Quantity >= CAST(@ProductQuantity AS int)"

    Using conn As SqlConnection = New SqlConnection(constr)
        conn.Open()
        Dim cmd As SqlCommand = New SqlCommand()
        cmd.Connection = conn
        cmd.CommandType = CommandType.Text
        cmd.CommandText = sql
        cmd.Parameters.AddWithValue("@ProductCode", CustomerDGV.Rows(i).Cells(0).Value)
        cmd.Parameters.AddWithValue("@ProductQuantity", CustomerDGV.Rows(i).Cells(1).Value)
        Dim rows As Integer = cmd.ExecuteNonQuery()

        If rows = 0 Then
            MessageBox.Show($"Make sure {CustomerDGV.Rows(i).Cells(0).Value} ProductQuantity <= Product_Quantity")
        End If
    End Using
Next

注意：这是一个 SQL 服务器演示。