Question

I am using SQL broker to do some asynchronous tasks(In my case sending mails). But the problem I am having is the stored procedure which is run when the the value is inserted to the queue runs twice every time the XML message is passed from a Trigger to the queue.

I have a message type:

CREATE MESSAGE TYPE MailMessage
AUTHORIZATION dbo 
VALIDATION = WELL_FORMED_XML

I have a contract:

CREATE CONTRACT MailContract
AUTHORIZATION dbo 
(MailMessage SENT BY INITIATOR)

I have a Queue:

    CREATE QUEUE dbo.MessageQueue
WITH STATUS=ON, 
 ACTIVATION ( 
 PROCEDURE_NAME = MailExecuter , 
 MAX_QUEUE_READERS = 1,
 EXECUTE AS OWNER );

I have two services:

    CREATE SERVICE MailSendActivator  
AUTHORIZATION dbo  
ON QUEUE dbo.MessageQueue (MailContract) ; // I have removed this the contract to make it a initiator but it did not worked out  

-- Create target Service   
CREATE SERVICE MailSendExec  
AUTHORIZATION dbo   
ON QUEUE dbo.MessageQueue (MailContract);  

Here is my trigger:

 CREATE TRIGGER MailSendTrigOnMailQueue ON dbo.MailQueue
 FOR INSERT 
 As  
 SET NOCOUNT ON;   

DECLARE @MessageBody XML  
DECLARE @TableId int  


SET @MessageBody = (SELECT CreatedDateTime,[Subject], MailType FROM inserted  
FOR XML AUTO)  


If (@MessageBody IS NOT NULL)  
BEGIN  

DECLARE @Handle UNIQUEIDENTIFIER;   
BEGIN DIALOG CONVERSATION @Handle   
FROM SERVICE MailSendActivator   
TO SERVICE 'MailSendExec'   
ON CONTRACT MailContract   
WITH ENCRYPTION = OFF;   

SEND ON CONVERSATION @Handle MESSAGE TYPE MailMessage(@MessageBody);   

END 

I have a stored procedure:
In the stored procedure I am Inserting values to a test table whether the stored procedure is running.

Stored Procedure:

    CREATE PROCEDURE dbo.MailExecuter  
AS   
BEGIN   

DECLARE @msgBody XML    
DECLARE @dlgId uniqueidentifier 
Insert into TestTable(Name, Test) values('MEX','test'); 
WHILE (1 = 1)   
    BEGIN 

            WAITFOR ( RECEIVE TOP(1) @msgBody = CAST(message_body AS XML),     @dlgId = conversation_handle  FROM dbo.MessageQueue ), TIMEOUT 500    
            IF (@@ROWCOUNT = 0 OR @msgBody IS NULL) 
                BEGIN   
                    BREAK   
                END   
            ELSE   
                BEGIN 


                 DECLARE @Subject nvarchar(200), @CreatedDateTime datetime, @MailType nvarchar(50)


                ---EXEC dbo.SendMails 1,1;

                END  
            END CONVERSATION @dlgId

            END  

    END 

But the stored procedure is running twice and populate my test table twice. I think the problem is with the send conversation part in the trigger.

I have been struck on this for a long time. Please, Can some one help me on this

Answer 1

You need to add to the RECEIVEprojection list the message_type_name. You must look at what message type you received and only call the mailing routine when the message type is MailMessage. As things are, you will always get a second message, the one from your END DIALOG. You simply need to call END DIALOG again on that case, to close the sending side handle:

  WAITFOR ( 
      RECEIVE TOP(1) 
         @msgBody = CAST(message_body AS XML),     
         @dlgId = conversation_handle ,
          @msgType = message_type_name
       FROM dbo.MessageQueue ), TIMEOUT 500    
    IF (@@ROWCOUNT = 0 OR @msgBody IS NULL) 
       BREAK   
    ELSE IF @msgType = N'MailMessage'   
    BEGIN 
       DECLARE @Subject nvarchar(200), @CreatedDateTime datetime, @MailType nvarchar(50)
       ---EXEC dbo.SendMails 1,1;
    END  

    END CONVERSATION @dlgId;

Any particular reason you are re-inventing the wheel? This is pretty much how sp_send_dbmail already works (except is using external activation).