c# - 比较数据集值

Question

在 winform 中，我试图将返回的数据集值与定义的值进行比较，但出现以下错误。

在下面的代码中，我将字符串从列表框传递给 GetStock 方法

public bool checkStock()
        {
            foreach (var listBoxItem in listBox1.Items)
            {
                if (Convert.ToInt32(GetStock(listBoxItem.ToString())) == 0)
                {
                    MessageBox.Show(listBoxItem.ToString() + " not in Stock!. Please delete the item before proceeding");
                    return false;
                }
            }
            return true;
        }

GetStock() 的代码

 public DataSet GetStock(string product)
        {
            DataSet dataSet = new DataSet();
            OleDbConnection oleConn = new OleDbConnection(connString);

            try
            {
                oleConn.Open();
                string sql = "SELECT [Quantity] FROM [Product] WHERE [Product Name]='" + product + "'";
                OleDbDataAdapter dataAdapter = new OleDbDataAdapter(sql, oleConn);
                dataAdapter.Fill(dataSet, "Product");
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex.ToString());
            }
            finally
            {
                oleConn.Close();
            }
            if (dataSet.Tables["Product"].Rows.Count <= 0)
                return null;

            return dataSet;
        }

    }
}

在数据库中，“数量”是字符串格式。

Answer 1

GetStock 返回一个 DataSet 但您将其传递给 Convert.ToInt32:

if (Convert.ToInt32(GetStock(listBoxItem.ToString())) == 0)

你可能想要这样的东西:

int stockCount = GetStockQuantity(listBoxItem.ToString());
if (stockCount == 0)
{
    MessageBox.Show(listBoxItem.ToString() + " not in Stock!. Please delete the item before proceeding");
}

这里是修改后的方法(注意我用的是参数)

public int GetStockQuantity(string product)
{
    int quantity = 0;
    string sql = "SELECT TOP 1 [Quantity] FROM [Product] WHERE [Product Name] = ?";
    using(var oleConn = new OleDbConnection(connString))
    using(var cmd = new OleDbCommand(sql , oleConn))
    {
        cmd.Parameters.AddWithValue("?", product);
        try
        {
            oleConn.Open();
            object obj_quantity = cmd.ExecuteScalar();
            if(obj_quantity != null)
                // "In database the "Quantity" is in string format." 
                // Change it to int if possible
                int.Parse((string)obj_quantity);
        }
        catch (Exception ex)
        {
            Console.WriteLine(ex.ToString());
        }
    }
    return quantity;
}