9. 客戶端/服務器

Now that we have seen how transactions work in db4o conceptually, we?are prepared to tackle concurrently executing transactions.
現在我們已經明白db4o中事務的概念了，本章講處理并行執行的事務。

現在按照以往熟悉的方法準備數據。
//?setFirstCar
Pilot?pilot?=?new?Pilot("Rubens?Barrichello",?99);
Car?car?=?new?Car("BMW");
car.Pilot?=?pilot;
db.Set(car);
//?setSecondCar
Pilot?pilot?=?new?Pilot("Michael?Schumacher",?100);
Car?car?=?new?Car("Ferrari");
car.Pilot?=?pilot;
db.Set(car);

9.1. 嵌入式服務器

• 從API角度看，分布式事務和單一VM上的事務沒有什么本質區別。在單機上使用事務，我們需要打開db4o服務器，指示它從0端口運行，從而其他的網絡程序不可以占用。
  
  

//?accessLocalServer
IObjectServer?server?=?Db4oFactory.OpenServer(Util.YapFileName,?0);
try
{
????IObjectContainer?client?=?server.OpenClient();
????//?Do?something?with?this?client,?or?open?more?clients
????client.Close();
}
finally
{
????server.Close();
}

• 再次委托打開和關閉數據庫的服務器作為運行環境，從而捕捉客戶端交互。

//?queryLocalServer
IObjectContainer?client?=?server.OpenClient();
ListResult(client.Get(new?Car(null)));
client.Close();

• 這個事務的級別在db4o里面被成為“read committed”。但是，每個客戶端維護它自己的已知對象緩存的引用。為了讓其他客戶端的變化快速執行，我們需要在服務器端直接引用已知的對象。我們將這個任務代理為一個專門的ListResult（）方法的版本。

public?static?void?ListRefreshedResult(IObjectContainer?container,?IObjectSet?items,?int?depth)
{
????Console.WriteLine(items.Count);
????foreach?(object?item?in?items)
????{????
????????container.Ext().Refresh(item,?depth);
????????Console.WriteLine(item);
????}
}
//?demonstrateLocalReadCommitted
IObjectContainer?client1?=server.OpenClient();
IObjectContainer?client2?=server.OpenClient();
Pilot?pilot?=?new?Pilot("David?Coulthard",?98);
IObjectSet?result?=?client1.Get(new?Car("BMW"));
Car?car?=?(Car)result.Next();
car.Pilot?=?pilot;
client1.Set(car);
ListResult(client1.Get(new?Car(null)));
ListResult(client2.Get(new?Car(null)));
client1.Commit();
ListResult(client1.Get(typeof(Car)));????????????
ListRefreshedResult(client2,?client2.Get(typeof(Car)),?2);
client1.Close();
client2.Close();
會滾也可以這樣工作，就像你預料的一樣：//?demonstrateLocalRollback
IObjectContainer?client1?=?server.OpenClient();
IObjectContainer?client2?=?server.OpenClient();
IObjectSet?result?=?client1.Get(new?Car("BMW"));
Car?car?=?(Car)result.Next();
car.Pilot?=?new?Pilot("Someone?else",?0);
client1.Set(car);
ListResult(client1.Get(new?Car(null)));
ListResult(client2.Get(new?Car(null)));
client1.Rollback();
client1.Ext().Refresh(car,?2);
ListResult(client1.Get(new?Car(null)));
ListResult(client2.Get(new?Car(null)));
client1.Close();
client2.Close();

9.2. 網絡

From here it's only a small step towards operating db4o over a TCP/IP network.?We just specify a port number greater than zero?and set up one or more accounts for our client(s).
到了這里，距離通過TCP/IP協議操作db4o沒有多少步驟了。我們需要專門指定一個大于0的端口號碼，為客戶端設置一個或者更多的帳戶。//?accessRemoteServer
IObjectServer?server?=?Db4oFactory.OpenServer(Util.YapFileName,?ServerPort);
server.GrantAccess(ServerUser,?ServerPassword);
try
{
????IObjectContainer?client?=?Db4oFactory.OpenClient("localhost",?ServerPort,?ServerUser,?ServerPassword);
????//?Do?something?with?this?client,?or?open?more?clients
????client.Close();
}
finally
{
????server.Close();
}


.
這個客戶端的連接需要提供一個主機、端口、用戶名和密碼。

//?queryRemoteServer
IObjectContainer?client?=?Db4oFactory.OpenClient("localhost",?port,?user,?password);
ListResult(client.Get(new?Car(null)));
client.Close();

• 剛才的所有數據都通過上面的例子檢索出來了

//?demonstrateRemoteReadCommitted
IObjectContainer?client1?=?Db4oFactory.OpenClient("localhost",?port,?user,?password);
IObjectContainer?client2?=?Db4oFactory.OpenClient("localhost",?port,?user,?password);
Pilot?pilot?=?new?Pilot("Jenson?Button",?97);
IObjectSet?result?=?client1.Get(new?Car(null));
Car?car?=?(Car)result.Next();
car.Pilot?=?pilot;
client1.Set(car);
ListResult(client1.Get(new?Car(null)));
ListResult(client2.Get(new?Car(null)));
client1.Commit();
ListResult(client1.Get(new?Car(null)));
ListResult(client2.Get(new?Car(null)));
client1.Close();
client2.Close();
//?demonstrateRemoteRollback
IObjectContainer?client1?=?Db4oFactory.OpenClient("localhost",?port,?user,?password);
IObjectContainer?client2?=?Db4oFactory.OpenClient("localhost",?port,?user,?password);
IObjectSet?result?=?client1.Get(new?Car(null));
Car?car?=?(Car)result.Next();
car.Pilot?=?new?Pilot("Someone?else",?0);
client1.Set(car);
ListResult(client1.Get(new?Car(null)));
ListResult(client2.Get(new?Car(null)));
client1.Rollback();
client1.Ext().Refresh(car,2);
ListResult(client1.Get(new?Car(null)));
ListResult(client2.Get(new?Car(null)));
client1.Close();
client2.Close();

9.3. 消息傳輸

• 有時候客戶端需要請求服務器做一些事情，就要發送一個特殊的消息給服務器。服務器需要接受消息、發送消息到涉及的對象。

• 可以通過SETMESSAGERECIPIENT()方法，找到發送消息的對象。
  
  

public?void?RunServer()
{
????lock(this)
????{
????????IObjectServer?db4oServer?=?Db4oFactory.OpenServer(FILE,?PORT);
????????db4oServer.GrantAccess(USER,?PASS);
????????
????????//?Using?the?messaging?functionality?to?redirect?all
????????//?messages?to?this.processMessage
????????db4oServer.Ext().Configure().ClientServer().SetMessageRecipient(this);
????????try
????????{
????????????if?(!?stop)
????????????{
????????????????//?wait?forever?for?Notify()?from?Close()
????????????????Monitor.Wait(this);
????????????}
????????}
????????catch?(Exception?e)
????????{
????????????Console.WriteLine(e.ToString());
????????}
????????db4oServer.Close();
????}
}
消息已經接收到了，并且被PROCESSMESSAGE() 方法傳遞。




db4o允許一個客戶端以無格式的類的對象的形式發送一個任意的消息或者信號給服務器。服務器收到后會發回一個收到消息，包含從客戶發來的對象。服務器可以任意定義消息的格式。

9.4. 整合--一個簡單但是完整的db4oserver

• 讓我們將以上的信息整合，從而寫出一個帶有專門客戶端的簡單服務器，客戶端可以通知服務器關閉。
  
  

• 首先，服務器和客戶端都需要一些共享的設置信息。我們提供一個接口：

namespace?Db4objects.Db4o.Tutorial.F1.Chapter5
{
????/**////?<summary>
????///?Configuration?used?for?StartServer?and?StopServer.
????///?</summary>
????public?class?ServerConfiguration
????{
????????/**////?<summary>
????????///?the?host?to?be?used.
????????///?If?you?want?to?run?the?client?server?examples?on?two?computers,
????????///?enter?the?computer?name?of?the?one?that?you?want?to?use?as?server.?
????????///?</summary>
????????public?const?string?HOST?=?"localhost";??
????????/**////?<summary>
????????///?the?database?file?to?be?used?by?the?server.
????????///?</summary>
????????public?const?string?FILE?=?"formula1.yap";
????????/**////?<summary>
????????///?the?port?to?be?used?by?the?server.
????????///?</summary>
????????public?const?int?PORT?=?4488;
????????/**////?<summary>
????????///?the?user?name?for?access?control.
????????///?</summary>
????????public?const?string?USER?=?"db4o";
????
????????/**////?<summary>
????????///?the?pasword?for?access?control.
????????///?</summary>
????????public?const?string?PASS?=?"db4o";
????}
}

創建server：锘縰sing?System;
using?System.Threading;
using?Db4objects.Db4o;
using?Db4objects.Db4o.Messaging;
namespace?Db4objects.Db4o.Tutorial.F1.Chapter5
{
????/**////?<summary>
????///?starts?a?db4o?server?with?the?settings?from?ServerConfiguration.
????///?This?is?a?typical?setup?for?a?long?running?server.
????///?The?Server?may?be?stopped?from?a?remote?location?by?running
????///?StopServer.?The?StartServer?instance?is?used?as?a?MessageRecipient
????///?and?reacts?to?receiving?an?instance?of?a?StopServer?object.
????///?Note?that?all?user?classes?need?to?be?present?on?the?server?side
????///?and?that?all?possible?Db4oFactory.Configure()?calls?to?alter?the?db4o
????///?configuration?need?to?be?executed?on?the?client?and?on?the?server.
????///?</summary>
????public?class?StartServer?:?ServerConfiguration,?IMessageRecipient
????{
????????/**////?<summary>
????????///?setting?the?value?to?true?denotes?that?the?server?should?be?closed
????????///?</summary>
????????private?bool?stop?=?false;
????????/**////?<summary>
????????///?starts?a?db4o?server?using?the?configuration?from
????????///?ServerConfiguration.
????????///?</summary>
????????public?static?void?Main(string[]?arguments)
????????{
????????????new?StartServer().RunServer();
????????}
????????/**////?<summary>
????????///?opens?the?IObjectServer,?and?waits?forever?until?Close()?is?called
????????///?or?a?StopServer?message?is?being?received.
????????///?</summary>
????????public?void?RunServer()
????????{
????????????lock(this)
????????????{
????????????????IObjectServer?db4oServer?=?Db4oFactory.OpenServer(FILE,?PORT);
????????????????db4oServer.GrantAccess(USER,?PASS);
????????????????
????????????????//?Using?the?messaging?functionality?to?redirect?all
????????????????//?messages?to?this.processMessage
????????????????db4oServer.Ext().Configure().ClientServer().SetMessageRecipient(this);
????????????????try
????????????????{
????????????????????if?(!?stop)
????????????????????{
????????????????????????//?wait?forever?for?Notify()?from?Close()
????????????????????????Monitor.Wait(this);
????????????????????}
????????????????}
????????????????catch?(Exception?e)
????????????????{
????????????????????Console.WriteLine(e.ToString());
????????????????}
????????????????db4oServer.Close();
????????????}
????????}
????????/**////?<summary>
????????///?messaging?callback
????????///?see?com.db4o.messaging.MessageRecipient#ProcessMessage()
????????///?</summary>
????????public?void?ProcessMessage(IObjectContainer?con,?object?message)
????????{
????????????if?(message?is?StopServer)
????????????{
????????????????Close();
????????????}
????????}
????????/**////?<summary>
????????///?closes?this?server.
????????///?</summary>
????????public?void?Close()
????????{
????????????lock(this)
????????????{
????????????????stop?=?true;
????????????????Monitor.PulseAll(this);
????????????}
????????}
????}
}



最后但并不是最不重要的(一點)，客戶端停止服務器。
锘縰sing?System;
using?Db4objects.Db4o;
using?Db4objects.Db4o.Messaging;
namespace?Db4objects.Db4o.Tutorial.F1.Chapter5
{
????/**////?<summary>
????///?stops?the?db4o?Server?started?with?StartServer.
????///?This?is?done?by?opening?a?client?connection
????///?to?the?server?and?by?sending?a?StopServer?object?as
????///?a?message.?StartServer?will?react?in?it's
????///?processMessage?method.
????///?</summary>
????public?class?StopServer?:?ServerConfiguration
????{
????????/**////?<summary>
????????///?stops?a?db4o?Server?started?with?StartServer.
????????///?</summary>
????????///?<exception?cref="Exception"?/>
????????public?static?void?Main(string[]?args)
????????{
????????????IObjectContainer?IObjectContainer?=?null;
????????????try
????????????{
????????????????//?connect?to?the?server
????????????????IObjectContainer?=?Db4oFactory.OpenClient(HOST,?PORT,?USER,?PASS);
????????????}
????????????catch?(Exception?e)
????????????{
????????????????Console.WriteLine(e.ToString());
????????????}
????????????
????????????if?(IObjectContainer?!=?null)
????????????{
????????????????//?get?the?messageSender?for?the?IObjectContainer
????????????????IMessageSender?messageSender?=?IObjectContainer.Ext()
????????????????????.Configure().ClientServer().GetMessageSender();
????????????????//?send?an?instance?of?a?StopServer?object
????????????????messageSender.Send(new?StopServer());
????????????????
????????????????//?close?the?IObjectContainer
????????????????IObjectContainer.Close();
????????????}
????????}
????}
}

9.5. 總結

db4o已經是一個家族了。不，當然他不是。有太多db4o沒有覆蓋的內容：schema 進展，為你的對象定制持久層，書寫你自己的查詢對象。。等等。更多的文檔需要提供，你也可下載獲得。
我們希望這個教程已經幫助你開始使用db4o，你該怎么繼續呢？

你應該瀏覽剩下的章節。他們是從我們的網站http://forums.db4o.com/forums/.選擇的話題。



（只是交互版本），實際上，這個教程只是基本的步驟而已，試著在章節間來回，運行代碼片段，你便可以完全掌握db4o。有時候，你有了困難，甚至發生異常，但是隨時可以在命令窗口重置數據庫。


這些例子都有源代碼。所以你可以自由的實驗。

如果遇到困難，看看FAQ有沒有作用。?在我們的web site瀏覽信息,?看看你的問題是否被提交到 Jira?，或者訪問我們的論壇：http://forums.db4o.com/forums/.

轉載于:https://www.cnblogs.com/xxpyeippx/archive/2007/05/06/737302.html

總結

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