Service Broker实现发布-订阅（Publish-Subscribe）框架(2)
关于发布-订阅框架的介绍，请访问前一篇 Service Broker实现发布-订阅（Publish-Subscribe）框架(1) 。
应用发布者逻辑
应用发布者逻辑
在存储过程sp_PublisherService 中实现PublisherService服务的入口点（entry point）。当一有新的消息到达PublisherQueue队列是，sp_PublisherService存储过程自动激活，并开始处理消息。这一存储过程能够处理如下消息类型：
[http://ssb.csharp.at/SSB_Book/c10/PublishMessage]: 在存储过程开始发布article消息时，它需要从AuthorService接收该消息类型。这一消息包含有如下article消息相同的主题（Subject）。
[http://ssb.csharp.at/SSB_Book/c10/SubscribeMessage]: 在存储过程准备订阅一个主题时，它需要从订阅者服务方接收该消息类型。这一消息包含有订阅者请求的主题。
[http://ssb.csharp.at/SSB_Book/c10/ArticleMessage]: 在存储过程发布article消息时，它会从AuthorService方接收这一消息类型。
[http://schemas.microsoft.com/SQL/ServiceBroker/EndDialog]: 在存储过程准备关闭PublisherService打开的会话时，存储过程会从AuthorService或订阅方服务接收这一消息类型。
[http://schemas.microsoft.com/SQL/ServiceBroker/Error]: 在请求的主题不存在是，存储过程将从PublisherService接收这一消息类型。
下面的script显示sp_PublisherService存储过程如何处理这些消息类型。
sp_PublisherService
服务处理程序：
CREATE PROCEDURE sp_PublisherService
AS
BEGIN
DECLARE @Conversation UNIQUEIDENTIFIER;
DECLARE @Message VARBINARY(MAX);
DECLARE @MessageTypeName SYSNAME;
BEGIN TRANSACTION;
WAITFOR
(
RECEIVE TOP(1)
@Conversation = conversation_handle,
@Message = message_body,
@MessageTypeName = message_type_name
FROM PublisherQueue
), TIMEOUT 1000;
WHILE (@Conversation IS NOT NULL)
BEGIN
IF (@MessageTypeName = 'http://ssb.csharp.at/SSB_Book/c10/PublishMessage')
BEGIN
EXEC sp_ProcessPublicationRequest @Conversation, @Message;
END
ELSE IF (@MessageTypeName ='http://ssb.csharp.at/SSB_Book/c10/SubscribeMessage')
BEGIN
EXEC sp_ProcessSubscriptionRequest @Conversation, @Message;
END
ELSE IF (@MessageTypeName ='http://ssb.csharp.at/SSB_Book/c10/ArticleMessage')
BEGIN
EXEC sp_SendOnPublication @Conversation, @Message;
END
ELSE IF (@MessageTypeName IN (
N'http://schemas.microsoft.com/SQL/ServiceBroker/Error',
N'http://schemas.microsoft.com/SQL/ServiceBroker/EndDialog'))
BEGIN
END CONVERSATION @Conversation;
IF (EXISTS (SELECT * FROM Publications WHERE Publication = @Conversation))
BEGIN
EXEC sp_RemovePublication @Conversation;
END
IF (EXISTS (SELECT * FROM Subscribers))
BEGIN
EXEC sp_RemoveSubscriber @Conversation;
END
END
ELSE
BEGIN
-- Unexpected message
RAISERROR (N'Received unexpected message type: %s', 16, 1,
@MessageTypeName);
ROLLBACK;
RETURN;
END
COMMIT;
SELECT @Conversation = NULL;
BEGIN TRANSACTION;
WAITFOR
(
RECEIVE TOP(1)
@Conversation = conversation_handle,
@Message = message_body,
@MessageTypeName = message_type_name
FROM PublisherQueue
), TIMEOUT 1000;
END
COMMIT;
END
GO
在上面的存储过程中，先从PublisherQueue队列中接收一个新的消息。如下消息类型为[http://ssb.csharp.at/SSB_Book/c10/PublishMessage]，就调用sp_ProcessPublicationRequest 存储过程，将接收到的发布数据记录到Publications表中。如果为[http://ssb.csharp.at/SSB_Book/c10/SubscribeMessage] 消息类型，则调用sp_ProcessSubscriptionRequest 存储过程，负责将接收到的订阅数据记录到Subscriptions表中。最后，如果为 [http://ssb.csharp.at/SSB_Book/c10/ArticleMessage]消息类型，则sp_PublisherService存储过程负责调用sp_SendOnPublication 分发该消息给所有匹配的订阅者。
通过sp_ProcessPublicationRequest 和sp_ProcessSubscriptionRequest 存储过程来管理发布和订阅记录。这2个存储过程分别调用其他的存储过程，将接收到的消息插入到Publications 或 Subscriptions 表中。如下显示 the sp_ProcessPublicationRequest 存储过程。因为sp_ProcessSubscriptionRequest 存储过程比较相似，这里忽略该存储过程。
sp_ProcessPublicationRequest
存储过程脚本：
CREATE PROCEDURE sp_ProcessPublicationRequest
@Conversation UNIQUEIDENTIFIER,
@Message VARBINARY(MAX)
AS
BEGIN
DECLARE @Request XML;
DECLARE @Subject NVARCHAR(MAX);
SELECT @Request = CAST(@Message AS XML);
WITH XMLNAMESPACES (DEFAULT 'http://ssb.csharp.at/SSB_Book/c10/PublishSubscribe')
SELECT @Subject = @Request.value(N'(//Publish/Subject)[1]', N'NVARCHAR(MAX)');
IF (@Subject IS NOT NULL)
BEGIN
EXEC sp_PublishPublication @Conversation, @Subject, @Message;
END
ELSE
BEGIN
END CONVERSATION @Conversation
WITH ERROR = 1
DESCRIPTION = N'The publication is missing a subject';
EXEC sp_RemovePublication @Conversation;
END
END
GO
sp_ProcessPublicationRequest存储过程调用sp_PublishPublication，并传入@Conversation, @Subject, @Message 三个参数。如下是sp_PublishPublication 存储过程。
sp_PublishPublication
存储过程脚本：
CREATE PROCEDURE sp_PublishPublication
@Publication UNIQUEIDENTIFIER,
@Subject NVARCHAR(MAX),
@OriginalXml XML
AS
BEGIN
INSERT INTO
Publications (Publication, Subject, OriginalXml)
VALUES
(
@Publication,
@Subject,
@OriginalXml
)
END
GO
Publications 表中的Publication列和Subscriptions表中的Subscription 列都存放会话ID，你需要这些会话ID来发送article消息到订阅方。最后一个存储过程是sp_SendOnPublication，在有[http://ssb.csharp.at/SSB_Book/c10/ArticleMessage] 消息从 AuthorService接收到后，调用才存储过程。
sp_SendOnPublication
存储过程脚本：
CREATE PROCEDURE sp_SendOnPublication
@Publication UNIQUEIDENTIFIER,
@Article VARBINARY(MAX)
AS
BEGIN
DECLARE @Subscription UNIQUEIDENTIFIER;
DECLARE @cursorSubscriptions CURSOR;
SET @cursorSubscriptions = CURSOR LOCAL SCROLL FOR
SELECT Subscriber
FROM Subscriptions s
JOIN Publications p ON s.Subject = p.Subject
WHERE p.Publication = @Publication;
BEGIN TRANSACTION;
OPEN @cursorSubscriptions;
FETCH NEXT FROM @cursorSubscriptions
INTO @Subscription;
WHILE (@@fetch_status = 0)
BEGIN
IF (@Article IS NOT NULL)
BEGIN
SEND ON CONVERSATION @Subscription
MESSAGE TYPE [http://ssb.csharp.at/SSB_Book/c10/ArticleMessage] (@Article);
END
ELSE
BEGIN
SEND ON CONVERSATION @Subscription
MESSAGE TYPE [http://ssb.csharp.at/SSB_Book/c10/ArticleMessage];
END
FETCH NEXT FROM @cursorSubscriptions INTO @Subscription;
END
CLOSE @cursorSubscriptions;
DEALLOCATE @cursorSubscriptions;
COMMIT;
END
GO
sp_SendOnPublication 存储过程使用一个cusor，发送从AuthorService接收到的article消息，给匹配的订阅者。
SEND ON CONVERSATION @Subscription
MESSAGE TYPE [http://ssb.csharp.at/SSB_Book/c10/ArticleMessage] (@Article);
通过对Publications 和 Subscriptions 表的Subject 字段进行连接，进行匹配：
SELECT Subscriber
FROM Subscriptions s
JOIN Publications p ON s.Subject = p.Subject
WHERE p.Publication = @Publication;
当接收到的是[http://schemas.microsoft.com/SQL/ServiceBroker/EndDialog] 消息类型时（从AuthorService或从订阅者服务方），相应的发布或订阅数据则需要从Publications或Subscriptions表中删除。分别通过sp_RemovePublication 或 sp_RemoveSubscriptions 存储过程来实现。
sp_RemovePublication
存储过程脚本：
CREATE PROCEDURE sp_RemovePublication
@Publication UNIQUEIDENTIFIER
AS
BEGIN
DELETE FROM Publications
WHERE Publication = @Publication
END
GO
EntLib.com译者注：本文翻译Apress出版《Pro SQL Server 2005 Service Broker》的其中一个章节。后面的内容会尽快发布，欢迎交流、分享。谢谢！