MQRead() function

The MQRead() function returns a message from WMQ without removing the message from the queue.

Syntax


1  MQREAD (?  service_name?  , policy_name?  , correl_id  )
service_name
Optional parameter. Refers to the value in the servicename column of the "informix".mqiservice table. If service_name is not specified, IDS.DEFAULT.SERVICE is used as the service. The maximum size of service_name is 48 bytes.
policy_name
Optional parameter. Refers to the value in the policyname column of the "informix".mqipolicy table. If policy_name is not specified, IDS.DEFAULT.POLICY is used as the policy. The maximum size of policy_name is 48 bytes.
correl_id
Optional parameter. A string containing a correlation identifier to be associated with this message. The correl_id is often specified in request and reply scenarios to associate requests with replies. The maximum size of correl_id is 24 bytes. If not specified, no correlation ID is added to the message.

Usage

The MQRead() function returns a message from the WMQ queue specified by service_name, using the quality of service policy defined in policy_name. This function does not remove the message from the queue associated with service_name. If correl_id is specified, then the first message with a matching correlation ID is returned. If correl_id is not specified, then the message at the head of the queue is returned. The result of the function is a string of type LVARCHAR. If no messages are returned, this function returns NULL. This function only reads committed messages.

The following table describes how the arguments for the MQRead() function are interpreted.
Table 1. MQRead() argument interpretation
Usage Argument interpretation
MQRead() No arguments
MQRead(arg1) arg1 = service_name
MQRead(arg1, arg2) arg1 = service_name

arg2 = policy_name
MQRead(arg1, arg2, arg3) arg1 = service_name

arg2 = policy_name

arg3 = correl_id

Return codes

A string of type LVARCHAR
The operation was successful.
NULL
No Messages are available.
Error
The operation was unsuccessful.

Examples

Example 1
begin;
EXECUTE FUNCTION MQRead();
commit;
Alternatively, the following syntax can be used:
insert into my_order_table VALUES(MQRead());
This example reads the message at the head of the queue with the following parameters:
  • service_name: default service name
  • policy_name: default policy name
  • correl_id: None
Example 2
begin;
EXECUTE FUNCTION MQRead('MYSERVICE');
rollback;
Alternatively, the following syntax can be used:
insert into my_order_table VALUES(MQRead('MYSERVICE'));
This example reads the message at the head of the queue with the following parameters:
  • service_name: "MYSERVICE"
  • policy_name: default policy name
  • correl_id: None
Example 3
begin;
EXECUTE FUNCTION MQRead('MYSERVICE','MYPOLICY');
commit;
Alternatively, the following syntax can be used:
insert into my_order_table VALUES(MQRead('MYSERVICE', 'MYPOLICY'));
This example reads the message at the head of the queue with the following parameters:
  • service_name: "MYSERVICE"
  • policy_name: "MYPOLICY"
  • correl_id: None
Example 4
begin;
EXECUTE FUNCTION MQRead('MYSERVICE','MYPOLICY', 'TESTS');
commit;
Alternatively, the following syntax can be used:
insert into my_order_table VALUES(MQRead('MYSERVICE', 'MYPOLICY', 'TESTS'));
This example reads the message at the head of the queue with the following parameters:
  • service_name: "MYSERVICE"
  • policy_name: "MYPOLICY"
  • correl_id: "TESTS"