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SQL Anywhere 10.0.1 » QAnywhere » QAnywhere SQL API Reference » Message management

ml_qa_getmessage Next Page

ml_qa_getmessagenowait


Returns the message ID of the next message that is currently queued for the given address.

Parameters

Item

Description

Remarks

1

Address

VARCHAR(128)

Return value

The message ID as VARCHAR(128).

Returns the message ID of the next message that is queued for the given address. Returns NULL if there is no queued message for this address.

Remarks

Use this stored procedure to check synchronously whether there is a message waiting for the specified QAnywhere message address. If you want a SQL procedure to be called asynchronously as soon as a message is available for a specified QAnywhere address, use the Listener.

For information on blocking until a message is available, see ml_qa_getmessage and ml_qa_getmessagetimeout.

The message corresponding to the returned message is not considered to be received until the current transaction is committed. Once the receive is committed, the message cannot be received again by this or any other QAnywhere API. Similarly, a rollback of the current transaction means that the message is not received, so subsequent calls to ml_qa_getmessage may return the same message ID.

The properties and content of the received message can be read by the various ml_qa_get stored procedures until a commit or rollback is executed on the current transaction. Once a commit or rollback is executed on the current transaction, the message data is no longer readable. Before committing, you should store any data you need from the message as tabular data or in SQL variables.

See also
Example

The following example displays the content of all messages that are queued at the address myaddress until all such messages are read (it is generally more efficient to commit after the last message has been read, rather than after each message is read):

begin
    declare @msgid varchar(128);
    loop
        set @msgid = ml_qa_getmessagenowait( 'myaddress' );
        if @msgid is null then leave end if;
        message 'a message with content ' || ml_qa_gettextcontent( @msgid ) || ' has been received';
    end loop;
    commit;
end