更新数据表中的值

本文关键字：数据表 更新 | 更新日期: 2023-09-27 18:33:27

当相同的书名插入购物车时，我试图更新我的数据表。 

public bool checkBook(DataTable dt, String title)
{
    bool returnval = false;
    try
    {
        foreach (DataRow dr in dt.Rows)
        {
            String checktitle = dr["Title"].ToString();
            if (title == checktitle)
            {
                int a = Convert.ToInt32(dr["quantity"].ToString());
                dr["quantity"] = a + 1;
                returnval = true;
            }
        }
    }
    catch (Exception ex)
    {
        //do something
    }
    return returnval;
}

数量中的初始值为 1，但提交按钮时，数量仍为 1，但当第三次输入时，数字才开始增加 1。我不明白错误在哪里？

编辑：： 

protected void ListView1_SelectedIndexChanged(object sender, EventArgs e)
{
    String title = ((Label)(ListView1.Items[ListView1.SelectedIndex].FindControl("Title"))).Text; ;
    decimal price = decimal.Parse(((Label)(ListView1.Items[ListView1.SelectedIndex].FindControl("Price"))).Text);
    cart cart = new cart(title, price);
    if (HttpContext.Current.Session["Cart"] != null)
    {
        DataTable shoppingcart = (DataTable)HttpContext.Current.Session["Cart"];
        bool check = checkBook(shoppingcart, title);
        if (check != true)
        {
            ShoppingCart.DataSource = cart.cartrow(shoppingcart);
            ShoppingCart.DataBind();
        }
        else
        {
            // if is true, it suppose to increase the quantity here 
            }
        }
    }
    else
    {
        HttpContext.Current.Session["Cart"] = cart.shoppingCart();
        ShoppingCart.DataSource = cart.shoppingCart();
        ShoppingCart.DataBind();
    }
}

.class：：

String title { get; set; }
decimal price { get; set; }
int quantity = 1;
DataTable CartTable;
DataRow tableRow;
public cart(String _title, decimal _price)
{
title = _title;
price = _price;
}
public DataTable shoppingCart()
{
CartTable = new DataTable("cart");
CartTable.Columns.Add("ID", typeof(Int32));
CartTable.Columns["ID"].AutoIncrement = true;
CartTable.Columns["ID"].AutoIncrementSeed = 1;
CartTable.Columns.Add("Title");
CartTable.Columns.Add("Price");
CartTable.Columns.Add("quantity");
CartTable.Columns["quantity"].DataType = typeof(Int32);
tableRow = CartTable.NewRow();
tableRow["Title"] = title;
tableRow["Price"] = price;
tableRow["quantity"] = quantity;
CartTable.Rows.Add(tableRow);
return CartTable;
}
public DataTable cartrow(DataTable _cart)
{
tableRow = _cart.NewRow();
tableRow["Title"] = title;
tableRow["Price"] = price;
tableRow["quantity"] = quantity;
_cart.Rows.Add(tableRow);
return _cart;
}

更新数据表中的值

您需要显示更多代码才能确定问题所在。是否绑定到数据表？单击按钮后是否重新创建它？

无论如何，下面是一些代码，以显示更新按预期工作。请注意使用System.Data.DataSetExtensions中的通用字段扩展方法。

namespace StackOverflowTestCode
{
    using System.Data;
    using Microsoft.VisualStudio.TestTools.UnitTesting;
    [TestClass]
    public class RandomTests
    {
        [TestMethod]
        public void DataTableUpdate_Test()
        {
            DataTable dataTable = new DataTable();
            dataTable.Columns.Add( "Title", typeof( string ) );
            dataTable.Columns.Add( "Quantity", typeof( int ) );
            dataTable.Rows.Add( "TitleOne", 0 );
            dataTable.Rows.Add( "TitleTwo", 0 );
            dataTable.Rows.Add( "TitleThree", 0 );
            DataRow[] rowsToUpdate = 
                dataTable.Select( "Title = 'TitleTwo'" );
            if( rowsToUpdate != null && rowsToUpdate.Length == 1 )
            {
                rowsToUpdate[ 0 ][ "Quantity" ] = 
                    rowsToUpdate[ 0 ].Field<int>( "Quantity" ) + 1;
            }
            // The right row was updated.
            Assert.AreEqual( 1, dataTable.Rows[ 1 ][ "Quantity" ] );
            // The other rows were not updated.
            Assert.AreEqual( 0, dataTable.Rows[ 0 ][ "Quantity" ] );
            Assert.AreEqual( 0, dataTable.Rows[ 2 ][ "Quantity" ] );
        }
    }
}

编辑

更新后，唯一立即跳出我的奇怪和可能的错误来源的是以下内容：

HttpContext.Current.Session["Cart"] = cart.shoppingCart(); 
ShoppingCart.DataSource = cart.shoppingCart();

你为什么要调用该方法两次？

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