ASP.NET网站数据库查询
--------------------编程问答-------------------- reader 返回的是一个集合列表，而你只读取了一次你应该循环读取
while(reader.Read())
{
//循环读取该用户选择的书ID
//然后根据ID得到该书的详细信息
}
其实你可以两个表做联合查询，然后读取该列表就可以了，包含订单和书的所有信息
select * from Order a inner join Book b on a.BookID=b.id --------------------编程问答-------------------- if (reader.Read())
改成while --------------------编程问答-------------------- OrderForm order = null;
if (reader.Read()) //这里要用While读取，reader.Read()每次 读取一条记录
{
order = new OrderForm();
order.BookID = (int)reader["BookID"];
}
IList<Book> book = BookManage.BookManager.GetBookBybookId(order .BookID );//order 是null的话，会出错，即使判断了，这里也只是最有一个order的book显示了。如果每个order只有一本书，放到前面的{}里面，否则的话可以用主从表，即先只显示Order，用户选择一个Order是，在显示Books
this.DataList1.DataSource = book;
this.DataList1.DataBind(); --------------------编程问答-------------------- 大神们说的是对的，+1 --------------------编程问答-------------------- if (reader.Read())这样是不行的
要用while 并且里面用List<T> .add 存起来 --------------------编程问答--------------------
假如说UserID对应的没有BookID,VS会报错,是因为 order.BookID = (int)reader["BookID"];你BookID为空的话，转换为整型肯定会报错的! --------------------编程问答-------------------- 错误说明楼上的几位说的都差不多，如果有疑问就接着问，闹明白儿的
上代码：
这是子查询方法，只访问一次数据库就可以了
Users user = (Users)Session["user"];
Users u = new Users();
u.UserID = user.UserID;
string sql = "select * from OrderForm where userID = '" + u.UserID + "'";
换成 string sql = "select BookID from OrderForm where userID = '" + u.UserID + "'";
//SqlDataReader reader = DBHelper.GetReader(sql);
//OrderForm order = null;
//if (reader.Read())
//{
//order = new OrderForm();
//order.BookID = (int)reader["BookID"];
//}
IList<Book> book = BookManage.BookManager.GetBookBybookId("-1 or BookID in("+sql+")" );
this.DataList1.DataSource = book;
this.DataList1.DataBind(); --------------------编程问答--------------------
--------------------编程问答--------------------
+1啊
或者楼主可以用dataset填充table啊 --------------------编程问答--------------------
错误提示不明显么？GetBookBybookId方法需要一个int型的ID，而你非要传一个字符串过去，要么重载方法，要么按该方法的传递参数来调用 --------------------编程问答--------------------
Users user = (Users)Session["user"];
Users u = new Users();
u.UserID = user.UserID;
string sql = "select * from OrderForm where userID = '" + u.UserID + "'";
SqlDataReader reader = DBHelper.GetReader(sql);
OrderForm order = null;
List<Book> booklist=new List<Book>();
while (reader.Read())
{
order = new OrderForm();
if(order.BookID!=null&&order.BookID.ToString()!="")
{
Book book=BookManage.BookManager.GetBookBybookId((int)reader["BookID"]; );
bookList.Add(book);
}
}
this.DataList1.DataSource = book;
this.DataList1.DataBind();
代码这么写 然后你在BookManage.BookManager.GetBookBybookId自己去写一个返回Book 的方法 --------------------编程问答--------------------
不好意思上面代码写错了：
这样子的：
--------------------编程问答-------------------- 得到一笔记录，是因为使用了等号：
Users user = (Users)Session["user"];
Users u = new Users();
u.UserID = user.UserID;
string sql = "select * from OrderForm where userID = '" + u.UserID + "'";
SqlDataReader reader = DBHelper.GetReader(sql);
List<Book> booklist=new List<Book>();
while (reader.Read())
{
if(reader["BookID"]!=null&&reader["BookID"].ToString()!="")
{
Book book=BookManage.BookManager.GetBookBybookId((int)reader["BookID"]; );
bookList.Add(book);
}
}
this.DataList1.DataSource = book;
this.DataList1.DataBind();
--------------------编程问答--------------------
调试运行后发现：我的DataList1中最多只能显示一条数据，想问下为什么呀？if 改成while
而且这个代码貌似还有一个问题就是，假如说UserID对应的没有BookID,VS会报错。
判断reader["BookID"]是否为空
--------------------编程问答--------------------
--------------------编程问答-------------------- 哦没看仔细，确实需要循环，这里只是读了一次而已 --------------------编程问答-------------------- Users user = (Users)Session["user"];
..
IList<Book> book = new List<Book>(); //这里创建一个集合
if (reader.Read())
{
order = new OrderForm();
order.BookID = (int)reader["BookID"];
...
//这里必须往集合里加数据，而不是在外面加。否则你加的永远是最后一条记录
}
Users u = new Users();
u.UserID = user.UserID;
string sql = "select * from OrderForm where userID = '" + u.UserID + "'";
SqlDataReader reader = DBHelper.GetReader(sql);
OrderForm order = null;
if (reader.Read())
{
order = new OrderForm();
order.BookID = (int)reader["BookID"];
}
IList<Book> book = BookManage.BookManager.GetBookBybookId(order .BookID );
this.DataList1.DataSource = book;
this.DataList1.DataBind();
你这样写根本不对，你想获得Users user = (Users)Session["user"];
Users u = new Users();
u.UserID = user.UserID;
string sql = "select * from OrderForm where userID = '" + u.UserID + "'";
SqlDataReader reader = DBHelper.GetReader(sql);
OrderForm order = null;
if (reader.Read())
{
order = new OrderForm();
order.BookID = (int)reader["BookID"];
}
IList<Book> book = BookManage.BookManager.GetBookBybookId(order .BookID );
this.DataList1.DataSource = book;
this.DataList1.DataBind();
你这样写更本就不对，你想获得UserID下的BookID的信息。你可以这样修改：
Users user = (Users)Session["user"];
Users u = new Users();
u.UserID = user.UserID;
string sql = "select * from OrderForm where userID = '" + u.UserID + "'";
SqlDataReader reader = DBHelper.GetReader(sql);
OrderForm order = null;
if (reader.Read())
{
order = new OrderForm();
order.BookID = (int)reader["BookID"];
}
IList<Book> book = BookManage.BookManager.GetBookBybookId(order .BookID );
this.DataList1.DataSource = book;
this.DataList1.DataBind();
你这样写根本不对，你想获得Users user = (Users)Session["user"];
Users u = new Users();
u.UserID = user.UserID;
string sql = "select * from OrderForm where userID = '" + u.UserID + "'";
SqlDataReader reader = DBHelper.GetReader(sql);
OrderForm order = null;
IList<Book> book = new List<Book>();
if (reader.Read())
{
order = new OrderForm();
order.BookID = (int)reader["BookID"];
book.Add(order);
}
//IList<Book> book = BookManage.BookManager.GetBookBybookId(order .BookID );
this.DataList1.DataSource = book;
this.DataList1.DataBind();
这样应该就可以了。
--------------------编程问答--------------------
IList<Book> booklist=new new List<Book>();
while(reader.Read())
{
Book book=new Book();
order = new OrderForm();
order.BookID = (int)reader["BookID"];
book = BookManage.BookManager.GetBookBybookId(order .BookID );
booklist.add(book);
｝
this.DataList1.DataSource = booklist;
this.DataList1.DataBind();
--------------------编程问答--------------------
Users user = (Users)Session["user"];
Users u = new Users();
u.UserID = user.UserID;
string sql = "select * from OrderForm where userID = '" + u.UserID + "'";
SqlDataReader reader = DBHelper.GetReader(sql);
OrderForm order = null;
while (reader.Read())
{
order = new OrderForm();
order.BookID = (int)reader["BookID"];
}
IList<Book> book = BookManage.BookManager.GetBookBybookId(order .BookID );
if(book!=null)
{
this.DataList1.DataSource = book;
this.DataList1.DataBind();
}
补充：.NET技术 , ASP.NET
