程序中有时会因要执行业务比较复杂, 运行时间长的一系统操作, 需要显示如 "执行中 .." 等用户友好提示,  可用ASP.NET AJAX 的 UpdatePanel & UpdateProgress 控件完成. 但若执行结果需要下载文件时, 则会出现执行完成但文件却下载不了的情况. 因为 UpdateProgress 是异步进行中.  解决方法可以建立一个 'DownloadFile.aspx' 页面作辅助, 请见如下主要代码片断  

-------  Data.aspx ----------- 

<asp:ScriptManager ID="ScriptManager" runat="server" /> 

<asp:UpdatePanel ID="UpdatePanel1" runat="server">
        <ContentTemplate> 

               <asp:UpdateProgress ID="UpdateProgress1" runat="server" DisplayAfter="2" DynamicLayout="true">
                            <ProgressTemplate>
                                <img src='<%=CommonUrl.Images %>wait_clock.gif' />
                                <span id='spanProgressNote'></span>
                            </ProgressTemplate>
              </asp:UpdateProgress>

         </ContentTemplate>
</asp:UpdatePanel>  

 <script language="javascript">

        Sys.WebForms.PageRequestManager.getInstance().add_initializeRequest(initializeRequestHandler);

        function initializeRequestHandler(sender, e) {
            var postBackElementId = e.get_postBackElement().id;

            switch (postBackElementId) {
                case '<%= btnSearch.ClientID %>':
                    spanProgressNote.innerHTML = 'Loading ..';
                    break;

                case '<%= imgExport.ClientID %>':
                    spanProgressNote.innerHTML = 'Exporting ..';
                    break;
              }                      

         }       

</script>

-------  Data.cs ----------- 

protected void imgExport_Click(object sender, ImageClickEventArgs e)
 {
        ...

       // SimpleWebUtils.DownloadFile(Response, filePath, Path.GetFileName(filePath));     // 不能直接在当前页下载文件 

        ScriptManager.RegisterStartupScript(this, this.GetType(), "RegisterStartupScript"
                                                , String.Format("window.navigate('../Control/'DownloadFile.aspx?path={0}');", Server.UrlEncode(filePath)), true);

        //ScriptManager.RegisterStartupScript(this, this.GetType(), "RegisterStartupScript"
        //                                       , String.Format("window.navigate('{0}');", fileUrl), true);      // 用这种方式可以不用 ''DownloadFile.aspx' 页面但下载文件直接打开是用网页方式而不是实际文件方式 (如: Excel)

 }

-------  DownloadFile.cs -----------

 protected void Page_Load(object sender, EventArgs e)
 {
        string path = Request.QueryString["path"];
        SimpleWebUtils.DownloadFile(Response, path, Path.GetFileName(path));
        ScriptManager.RegisterStartupScript(this, this.GetType(), "RegisterStartupScript", "window.close();", true);                                                
 }

在 Oracle Procedure 中使用 IN 参数似乎很好地对该参数起到保护作用, 其实不然! 请看如下 Code

-- Spec Part 

PACKAGE TEST
IS
   g1   NUMBER;

   PROCEDURE proc1;

   PROCEDURE proc2 (p1 IN NUMBER);
END;        

-- Body Part

 PACKAGE BODY TEST
IS
   PROCEDURE proc1
   IS
   BEGIN
      g1 := 1;
      proc2 (g1);
      DBMS_OUTPUT.put_line ('g1=' || g1);
   END;

   PROCEDURE proc2 (p1 IN NUMBER)
   IS
      c1   CONSTANT NUMBER := p1;
   BEGIN
      --p1 := p1 + 1;  这句是编译不通过的, 似乎已对 IN 参数保护了.
      DBMS_OUTPUT.put_line ('p1=' || p1);
      DBMS_OUTPUT.put_line ('c1=' || c1);
      g1 := g1 + 1;  -- 这句间接地改变了 IN 参数值!
      DBMS_OUTPUT.put_line ('after p1=' || p1);   -- 已经被改了!
      DBMS_OUTPUT.put_line ('after c1=' || c1); 
   END;
END;

运行 proc1 后输出:

p1=1
c1=1
after p1=2
after c1=1
g1=2

总结:

1) 若要确保过程内任意地方都能访问到 IN 参数的初始值, 需要使用附加常量

2) 尽可能少用全局变量 (风险很大)

3) 其它非 Oracle 数据库也可能出现该情况.

实现如下:

<smic:Note runat=server ID='NoteInfo'>
     <b>Development Tools</b>
     <br />
     C#, JAVA, PHP
</smic:Note>

代码片段:

[ToolboxBitmap(typeof(Label))]
[AspNetHostingPermission(SecurityAction.Demand, Level = AspNetHostingPermissionLevel.Minimal)]
[AspNetHostingPermission(SecurityAction.InheritanceDemand, Level = AspNetHostingPermissionLevel.Minimal)]
[ToolboxData("<{0}:Note runat=\"server\"></{0}:Note>"), DefaultProperty("Message"), ParseChildren(false), Designer("System.Web.UI.Design.WebControls.LabelDesigner, System.Design, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a")]
[ControlBuilder(typeof(LabelControlBuilder)), ControlValueProperty("Message"), DataBindingHandler("System.Web.UI.Design.TextDataBindingHandler, System.Design, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a")]
public class Note : WebControl
{

        [PersistenceMode(PersistenceMode.InnerDefaultProperty), Bindable(true), Localizable(true)]       
        public string Message
        {
            get { return ViewState["Message"] as string; }
            set { ViewState["Message"] = value; }
        }

        protected override void AddParsedSubObject(object obj)        // 必须 Override WebControl 的 AddParsedSubObject 方法
        {
            if (this.HasControls())
            {
                base.AddParsedSubObject(obj);
            }
            else if (obj is LiteralControl)
            {
                this.Message = ((LiteralControl)obj).Text;
            }
            else
            {
                string message = this.Message;
                if (message.Length != 0)
                {
                    this.Message = string.Empty;
                    base.AddParsedSubObject(new LiteralControl(message));
                }
                base.AddParsedSubObject(obj);
            }
        }

        protected override void Render(HtmlTextWriter output)
        {
            output.AddAttribute("class", "container");
            output.RenderBeginTag(HtmlTextWriterTag.Div);
            output.Write(this.Message);
            output.RenderEndTag();            
        }

}

今天将 Lambda 与 yield 结合起来使用, 结果编译不通过. (如下)

public IEnumerable<int> DeletedIDs
{
    get
    {
       
        var deletedIDs = new int[]{123, 456};

        Array.ForEach(deletedIDs, i => (yield return i));

    }
}

要写成如下:

public IEnumerable<int> DeletedIDs
{
    get
    {
        
       var deletedIDs = new int[]{123, 456};

       foreach (int deletedID in deletedIDs)
           yield return deletedID;
    }
}

某些系统可能对系统应付数据高并发的响应要求比较高 (如: 飞行航空订票系统). 本文采用 Oracle 的 lock table 解决之.

Procedure 中关键 code 如下:

-------------------------------------------------------------

lock table tb_book_ticket in share mode;

...

insert into tb_book_ticket (id, scheduled_flight, ticket_no, book_time) values (ID.nextval, v_scheduled_flight, v_ticket_no, SYSDATE);    -- mark1

...    -- mark2

select count(*) into v_book_count from tb_book_ticket where scheduled_flight = v_scheduled_flight;    -- mark3

if v_book_count <= v_book_max_count then

    v_result := 'book successfully';

    commit;

else

    v_result := 'book unsuccessfully';

    rollback;

end if;

return v_result;

-------------------------------------------------------------

以上有2个地方需注意:

1) 采用 lock table table_name in share mode 方式而非 lock table table_name in exclusive mode 提高并发性处理, 尽量减少不必要执行等待.

2) 按常规思路, 可能会将 mark1 与 mark3 顺序交换, 但此举不行

-------------------------------------------------------------

select count(*) into v_book_count from tb_book_ticket where scheduled_flight = v_scheduled_flight;    -- mark3

...    -- mark2

if v_book_count < v_book_max_count then

    insert into tb_book_ticket (id, scheduled_flight, ticket_no, book_time) values (ID.nextval, v_scheduled_flight, v_ticket_no, SYSDATE);    -- mark1

     -- mark4

    commit;

end if;

-------------------------------------------------------------

试想若 userA 执行到  mark4, 而同时 userB 执行到  mark3, 就可能会出现由于 userA  尚未commit 而导致 userB 订到机票但实际没有座位的情况.

若确希望使用常规逻辑来实现, 需要用到 Oracle 的表的读锁功能 (精细访问策略), 而此非本文范围, 且其对于SYS用户无效.

使用情况:

1) 用户在 [查询页] 选取所需的 DropDown 项或填写查询的 TextBox 值

2) 点击结果表格的一条记录链接进入 [编辑页] (不是弹出 Form 形式, 而是整个页面跳转)

3) 在 [编辑页] 中修改有关项后保存 (保存后可能又进行修改后又保存)

4) 按 [Close] button 回 [查询页]

5) 要求 [查询页] 保留之前的查询状态 (即各DropDown, TextBox 项保留用户刚才选取或录入的值), 而表格数据则要求自动刷新 (因为刚才在 [编辑页] 中可能作了某些修改)

注意事项:

1) 因为 HTTP 的无状态性, 所以采用 Session 保留页面间的信息传递 (注意: 不能使用 URL 传递方式, 如: window.location.href = 'Search.aspx?serverRefreshed=yes', 因为这样页面原状态将不可还原 )

2) 由于 window.history.go(-N)  后页面的 cs 代码不会执行, 故采用 Ajax 方式调用服务端代码

代码片断:

----------------------------------------------------

Edit.aspx:

<asp:HiddenField ID="hfPostCount" runat="server"/>
<asp:button id="btnSave" runat="server" Text="Save" OnClientClick="document.getElementById(hfDataSaved).value = 'Yes'" OnClick="btnSave_Click"></asp:button>
<input type=button id="btnClose" value="Close" onclick="FormClose();" />

function FormClose()
{  
    if (document.getElementById(hfDataSaved).value == 'Yes') RRSCore.SessionInfo.SetServerRefreshed("No");       
    var postCount = document.getElementById(hfPostCount).value;
    postCount++;
    window.history.go(-postCount);
}       

----------------------------------------------------

Edit.aspx.cs:

protected void Page_Load(object sender, EventArgs e)
{
   if (!this.IsPostBack)
       hfPostCount.Value = "0";
   else
       hfPostCount.Value = (int.Parse(hfPostCount.Value) + 1).ToString(); 

   Page.ClientScript.RegisterStartupScript(Page.GetType(), "SetClientVariable", "hfPostCount='" + this.hfPostCount.ClientID.ToString() + "';", true);  
}

----------------------------------------------------

Search.aspx  

window.onload = function () {
    if (RRSCore.SessionInfo.GetServerRefreshed().value == 'No') document.forms[0].submit();              
    RRSCore.SessionInfo.SetServerRefreshed("Yes");
}

----------------------------------------------------

SessionInfo.cs (Ajax Source)

namespace RRSCore
{ 

    public class SessionInfo
    { 

         [AjaxPro.AjaxMethod]
         public static void SetServerRefreshed(string serverRefreshed)
         {
              HttpContext.Current.Session["ServerRefreshed"] = serverRefreshed;
         }

         [AjaxPro.AjaxMethod]
         public static string GetServerRefreshed()
         {
               return HttpContext.Current.Session["ServerRefreshed"];
         }

    }

}

----------------------------------------------------

 注意事项:

1) 前提是开发者机器要装有Framework 3.5, 引入Reference : System.Core

2)  若发布服务器没装 Framework 3.5, 需手工把 System.Core.dll 加入到 bin 下再发布

=========================================== 

using System.Linq;

..

string[] list = new string[] { "mary", "tom", "david", "cathy", "tom" };    // 除数组外,  其它集合类也可 (如: List, Hashtable , Dictionary)
IEnumerable<string> result;

//
Console.WriteLine("--- 'FirstOrDefault' --");
result = Enumerable.Where<string>(list,
                 delegate(string item)
                 {
                     return item == "tom";
                 });
Console.WriteLine(Enumerable.FirstOrDefault(result));

//
Console.WriteLine("--- 'OrderBy' --");
result = Enumerable.OrderBy<string, string>(list,
                delegate(string item)
                {
                    return item;
                });
foreach (string str in result)
{
    Console.WriteLine(str);
}

//
Console.WriteLine("--- 'Min' --");
string result_str = Enumerable.Min<string, string>(list,
                 delegate(string item)
                 {
                     return item;
                 });
Console.WriteLine(result_str);

//
Console.WriteLine("--- 'Distinct' --");
result = Enumerable.Distinct<string>(list);
foreach (string str in result)
{
    Console.WriteLine(str);
}

//
Console.WriteLine("--- 'All' --");
bool result_bool = Enumerable.All<string>(list, delegate(string item)
                 {
                     return item.CompareTo("d") > 0;
                 });
Console.WriteLine(result_bool);

//
Console.WriteLine("--- 'Distinct' & 'OrderBy' & 'Where' --");
result = Enumerable.Distinct<string>(Enumerable.OrderBy<string, string>(Enumerable.Where<string>(list,
                delegate(string item)
                {
                    return item == "tom" || item == "david";
                }),
                delegate(string item)
                {
                    return item;
                }));
foreach (string str in result)
{
    Console.WriteLine(str);
}

===========================================

输出如下: 

--- 'FirstOrDefault' --
tom
--- 'OrderBy' --
cathy
david
mary
tom
tom
--- 'Min' --
cathy
--- 'Distinct' --
mary
tom
david
cathy
--- 'All' --
False
--- 'Distinct' & 'OrderBy' & 'Where' --
david
tom
 

------------------------------------------------------------------------------------------------------------- 

--  procedure part

FUNCTION IIF (p_bool IN BOOLEAN, p_result1 IN ANYDATA, p_result2 IN ANYDATA)
   RETURN ANYDATA
IS
   atype                ANYTYPE;
   data_type_argument   EXCEPTION;
BEGIN
   IF p_result1.gettype (atype) <> p_result2.gettype (atype)
   THEN
      RAISE data_type_argument;
   END IF;

   CASE p_result1.gettype (atype)
      WHEN DBMS_TYPES.typecode_number
      THEN
         RETURN CASE
            WHEN p_bool
               THEN ANYDATA.convertnumber (p_result1.accessnumber)
            ELSE ANYDATA.convertnumber (p_result2.accessnumber)
         END;
      WHEN DBMS_TYPES.typecode_varchar2
      THEN
         RETURN CASE
            WHEN p_bool
               THEN ANYDATA.convertnvarchar2 (p_result1.accessvarchar2)
            ELSE ANYDATA.convertnvarchar2 (p_result2.accessvarchar2)
         END;
      WHEN DBMS_TYPES.typecode_date
      THEN
         RETURN CASE
            WHEN p_bool
               THEN ANYDATA.convertdate (p_result1.accessdate)
            ELSE ANYDATA.convertdate (p_result2.accessdate)
         END;
   END CASE;
EXCEPTION
   WHEN data_type_argument
   THEN
      DBMS_OUTPUT.put_line
          ('The data type of the ''IIF'' function both result parameter is different');
      RETURN NULL;
END;

-------------------------------------------------------------------------------------------------------------

--  caller part 

v_str                   VARCHAR2 (50)
         := iif (1 > 2,
                 ANYDATA.convertvarchar2 ('Yes'),
                 ANYDATA.convertvarchar2 ('No')
                ).accessnvarchar2;         

-- 类似于 C# 使用 string v_str = iif<string> (1> 2, 'Yes', 'No');

v_num                NUMBER
         := iif (1 > 2, ANYDATA.convertnumber (1), ANYDATA.convertnumber (0)).accessnumber;   

-- 类似于 C# 使用 int v_num = iif<int> (1> 2, 1, 0);

DBMS_OUTPUT.put_line (v_str);       -- output 'No' 

DBMS_OUTPUT.put_line (v_num);     -- output '0'

                                                                                  

且看如下2例

     低效:　            

             for (int i=1; i<=100; i++)   

                sum += i;

  (2) 计算1加到10000，奇数和偶数的总和。

   低效:　

  高效:　                 

今天写了个 DownloadWebFile 函数,  采用 读取 --> 输出 方式.  但发现当第二次打开 Download 的文件时, 文件报已损坏错误. code 如下:

protected void DownloadFile(string url)
  {
   System.Net.HttpWebRequest Myrq = (System.Net.HttpWebRequest)System.Net.HttpWebRequest.Create(url); 
   System.Net.HttpWebResponse myrp = (System.Net.HttpWebResponse)Myrq.GetResponse();
   Stream respStream = myrp.GetResponseStream();

   Response.Expires = 0;
   Response.Clear();

   Response.ContentType = myrp.ContentType;

   const int BUFFER_SIZE = 16*1024;
   byte[] buffer = new byte[BUFFER_SIZE];
   int length;   
   
   length = respStream.Read(buffer, 0, BUFFER_SIZE);
   while(length > 0)
   {
      Response.BinaryWrite(buffer);   
      length = respStream.Read(buffer, 0, BUFFER_SIZE);
   }

   Response.AddHeader("content-disposition", String.Format("attachment;filename={0}", "Competitor's list.xls"));
   Response.AddHeader("pragma", "no-cache");
   Response.AddHeader("expires", "0");
   Response.AddHeader("cache-control", "must-revalidate, post-check=0, pre-check=0");   

   Response.Flush();
   Response.End();   
  }

 后在 Wicky 同志的帮助下,  采用 读取 --> 中传站存放 -> 输出 方式得已解决 !

protected void DownloadFile(string url)
  {
   System.Net.HttpWebRequest Myrq = (System.Net.HttpWebRequest)System.Net.HttpWebRequest.Create(url); 
   System.Net.HttpWebResponse myrp = (System.Net.HttpWebResponse)Myrq.GetResponse();
   Stream respStream = myrp.GetResponseStream();

   Response.Expires = 0;
   Response.Clear();

   Response.ContentType = myrp.ContentType;

   const int BUFFER_SIZE = 16*1024;
   byte[] buffer = new byte[BUFFER_SIZE];
   int length;   
   
   MemoryStream ms = new MemoryStream();
   
   length = respStream.Read(buffer, 0, BUFFER_SIZE);
   while(length > 0)
   {
      ms.Write(buffer, 0, length);
      length = respStream.Read(buffer, 0, BUFFER_SIZE);
   }

   Response.AddHeader("content-disposition", String.Format("attachment;filename={0}", "Competitor's list.xls"));
   Response.AddHeader("pragma", "no-cache");
   Response.AddHeader("expires", "0");
   Response.AddHeader("cache-control", "must-revalidate, post-check=0, pre-check=0");   

   Response.BinaryWrite(ms.GetBuffer());

   Response.Flush();
   Response.End();   
  }

数据库 FireBird 求指定行数记录的 sql 语法不是Oracle的rownum，也不是SQL Server的Top n.  而是使用以下比较特别的形式.

1)  select First 2 skip 3 * from table1 order by field1 desc     -- 取第4行到第5行

2)  select * from table1 order by field1 desc ROWS 2 TO 4   -- 取第2行到第4行

3)  select First 3 skip 0 * from table1 order by field1 desc     -- 同 SQL Server 的 Top 3 

First n skip m形式会在忽略掉m行后，取前n行；

而rows m to n形式，则是从第m行取到第n行。

设有如下表 T

A   B
-----------
1   01
1   02
1   03
2   04
2   05
3   06

执行如下 sql

select a,replace(max(sys_connect_by_path(b,';')),';','') b
 from (select a,b,
 (row_number() over(order by a,b)
 + dense_rank() over(order by a)) rn,
 min(b) over(partition by a) mb
 from t
 )
 start with b = mb
 connect by rn-1 = prior rn
 group by a

可得如下结果

A   B
--------------------
1   010203
2   0405
3   06

假设有如下表: SALE_AMOUNT

BU      AMOUNT

=============

CRD             100

SHK             200

RSJ               500

运行如下 sql

ORDER BY BU

可得如下结果

BU    AMOUNT           AMOUNT_RATIO

================================

CRD            100                               0.0125

RSJ              500                                 0.625

SHK            200                                   0.25

Total            800                                        1

当它们激情碰撞时, 有两点是需要注意的:

1)      ratio_to_report (SUM (AMOUNT)) OVER () 中的SUM () 须写于内层而不能写于外层. 如SUM (ratio_to_report (AMOUNT) OVER ())

2)      ratio_to_report 后须乘以 2, 因为ratio_to_report (SUM (AMOUNT)) OVER () 已除多一个 total 了. 即AMOUNT / (2  *  TOTAL_ AMOUNT )

      今天用 CultureInfo 结合 ToString("MMM")  硬是不能取得英文月份表示 (如: Mar) , 而是中文 '三月'    (本人OS为中文版本).             

            CultureInfo info = new CultureInfo("en-US", false);
            Calendar calendar = info.Calendar;
            DateTime t = new DateTime(year, month, day, calendar);
            return t.ToString("MMM") + " " + t.Year.ToString();    // return '三月 2007'

     兜了几个圈子, 后改用 DateTimeFormatInfo class 才得以解决. 

            DateTimeFormatInfo myDTFI = new CultureInfo( "en-US", false ).DateTimeFormat;
            DateTime t = new DateTime(year, month, day);
            return myDTFI.GetAbbreviatedMonthName(t.Month) + " " + t.Year.ToString();    // return 'Mar 2007'

     令外,  DateTimeFormatInfo class 还有好多实用转换方法.  如:  

             myDTFI.GetDayName(t.DayOfWeek) --> Thursday

前提在运行多线程前提下.

因为在大多数计算机上，增加变量操作不是一个原子操作，需要执行下列步骤：

1. 将实例变量中的值加载到寄存器中。
2. 增加或减少该值。
3. 在实例变量中存储该值。

如果不使用 Interlocked  类的 Increment 和 Decrement，线程会在执行完前两个步骤后被抢先。然后由另一个线程执行所有三个步骤。当第一个线程重新开始执行时，它改写实例变量中的值，造成第二个线程执行增减操作的结果丢失。

请见如下例子: 

using System;
using System.Threading;

class Test
{
    static void Main()
    {
        Thread thread1 = new Thread(new ThreadStart(ThreadMethod));
        Thread thread2 = new Thread(new ThreadStart(ThreadMethod));
        thread1.Start();
        thread2.S