我正在为我的 ShoppingCart 需要的每个项目从 Northwind 数据库打开一个数据库查询。它是从桌子上拿走ProductID
的。在我从数据库中取出两列以将数据保存到. 然后我比较以确保用户输入的数量小于数据库中库存的列单位。UnitsInStock
Products
DataTabel ds
theCart.Values
是 ICollections 的一部分。
我遇到错误:来自我的异常消息:“连接到数据库时出现问题:对象引用未设置为对象的实例。”
这是代码。
DataSet ds = new DataSet();
OleDbConnection conn = new OleDbConnection((string)Application["DBConnectionString"]);
foreach (OrderItem item in theCart.Values)
{
string selectionString =
"SELECT Products.ProductID, Products.UnitsInStock " +
"FROM Products" +
"WHERE Products.ProductID = " + item.ProductID + ";";
try
{
OleDbCommand cm = new OleDbCommand(selectionString, conn);
OleDbDataAdapter da = new OleDbDataAdapter();
da.SelectCommand = cm;
da.Fill(ds);
da.Dispose();
if (ds.Tables["Products"].Columns.Count != 0 &&
ds.Tables["Products"].Rows.Count != 0)
{
for (int index = 0; index < ds.Tables["Products"].Rows.Count; index++)
{
if (item.ProductID == int.Parse(ds.Tables["Products"].Rows[index][indexOfProductID].ToString()))
{
if (item.QuantityOrdered > int.Parse(ds.Tables["Products"].Rows[index][indexOfUnitsInStock].ToString()))
{
hasStock = false;
int inStock = int.Parse(ds.Tables["Products"].Rows[index][indexOfUnitsInStock].ToString());
txtUnderstockedItems.Text += "Sorry we do not have enough stock of item: " + item.ProductName +
"<br> Currently, " + item.ProductName + " (ID:" + item.ProductID + ") has " + inStock + " in stock.";
}
else
{//can output how many items in stock here.
hasStock = true;
}
}
}
}
catch (Exception ex)
{
txtUnderstockedItems.Text = "There was a problem connecting to the database: " + ex.Message;
}
finally
{
conn.Close();
}
}
}