# 12. API: Advanced Queuing (AQ)

See Using Oracle Advanced Queuing (AQ) for more information about using AQ in python-oracledb.

Note

All of these objects are extensions to the DB API.

## 12.1. Queue Objects

These objects are created using the `Connection.queue()` method and are used to enqueue and dequeue messages.

### 12.1.1. Queue Methods

Queue.deqmany(maxMessages)

  Dequeues up to the specified number of messages from the queue and returns a list of these messages. Each element of the returned list is a message property object.

  For consistency and compliance with the PEP 8 naming style, the name of the method was changed from deqMany(). The old name will continue to work for a period of time.

Queue.deqone()

  Dequeues at most one message from the queue. If a message is dequeued, it will be a message property object; otherwise, it will be the value None.

  For consistency and compliance with the PEP 8 naming style, the name of the method was changed from deqOne(). The old name will continue to work for a period of time.

Queue.enqmany(messages)

  Enqueues multiple messages into the queue. The `messages` parameter must be a sequence containing message property objects which have all had their payload attribute set to a value that the queue supports.

  Warning

  Calling this function in parallel on different connections acquired from the same pool may fail due to Oracle bug 29928074. Ensure that this function is not run in parallel, use standalone connections or connections from different pools, or make multiple calls to `Queue.enqone()` instead. The function `Queue.deqmany()` call is not affected.

  For consistency and compliance with the PEP 8 naming style, the name of the method was changed from enqMany(). The old name will continue to work for a period of time.

Queue.enqone(message)

  Enqueues a single message into the queue. The message must be a message property object which has had its payload attribute set to a value that the queue supports.

  For consistency and compliance with the PEP 8 naming style, the name of the method was changed from enqOne(). The old name will continue to work for a period of time.

### 12.1.2. Queue Attributes

Queue.connection

  This read-only attribute returns a reference to the connection object on which the queue was created.

Queue.deqoptions

  This read-only attribute returns a reference to the options that will be used when dequeuing messages from the queue.

  For consistency and compliance with the PEP 8 naming style, the name of the attribute was changed from deqOptions. The old name will continue to work for a period of time.

Queue.enqoptions

  This read-only attribute returns a reference to the options that will be used when enqueuing messages into the queue.

  For consistency and compliance with the PEP 8 naming style, the name of the attribute was changed from enqOptions. The old name will continue to work for a period of time.

Queue.name

  This read-only attribute returns the name of the queue.

Queue.payload_type

  This read-only attribute returns the object type for payloads that can be enqueued and dequeued. If using a JSON queue, this returns the value `"JSON"`. If using a raw queue, this returns the value `None`.

  For consistency and compliance with the PEP 8 naming style, the name of the attribute was changed from payloadType. The old name will continue to work for a period of time.

## 12.2. Dequeue Options

Note

These objects are used to configure how messages are dequeued from queues. An instance of this object is found in the attribute `Queue.deqOptions`.

DeqOptions.condition

  This read-write attribute specifies a boolean expression similar to the where clause of a SQL query. The boolean expression can include conditions on message properties, user data properties and PL/SQL or SQL functions. The default is to have no condition specified.

DeqOptions.consumername

  This read-write attribute specifies the name of the consumer. Only messages matching the consumer name will be accessed. If the queue is not set up for multiple consumers this attribute should not be set. The default is to have no consumer name specified.

DeqOptions.correlation

  This read-write attribute specifies the correlation identifier of the message to be dequeued. Special pattern-matching characters, such as the percent sign (%) and the underscore (_), can be used. If multiple messages satisfy the pattern, the order of dequeuing is indeterminate. The default is to have no correlation specified.

DeqOptions.deliverymode

  This write-only attribute specifies what types of messages should be dequeued. It should be one of the values `MSG_PERSISTENT` (default), `MSG_BUFFERED` or `MSG_PERSISTENT_OR_BUFFERED`.

DeqOptions.mode

  This read-write attribute specifies the locking behaviour associated with the dequeue operation. It should be one of the values `DEQ_BROWSE`, `DEQ_LOCKED`, `DEQ_REMOVE` (default), or `DEQ_REMOVE_NODATA`.

DeqOptions.msgid

  This read-write attribute specifies the identifier of the message to be dequeued. The default is to have no message identifier specified.

DeqOptions.navigation

  This read-write attribute specifies the position of the message that is retrieved. It should be one of the values `DEQ_FIRST_MSG`, `DEQ_NEXT_MSG` (default), or `DEQ_NEXT_TRANSACTION`.

DeqOptions.transformation

  This read-write attribute specifies the name of the transformation that must be applied after the message is dequeued from the database but before it is returned to the calling application. The transformation must be created using dbms_transform. The default is to have no transformation specified.

DeqOptions.visibility

  This read-write attribute specifies the transactional behavior of the dequeue request. It should be one of the values `DEQ_ON_COMMIT` (default) or `DEQ_IMMEDIATE`. This attribute is ignored when using the `DEQ_BROWSE` mode. Note the value of `autocommit` is always ignored.

DeqOptions.wait

  This read-write attribute specifies the time to wait, in seconds, for a message matching the search criteria to become available for dequeuing. One of the values `DEQ_NO_WAIT` or `DEQ_WAIT_FOREVER` can also be used. The default is `DEQ_WAIT_FOREVER`.

## 12.3. Enqueue Options

Note

These objects are used to configure how messages are enqueued into queues. An instance of this object is found in the attribute `Queue.enqOptions`.

EnqOptions.deliverymode

  This write-only attribute specifies what type of messages should be enqueued. It should be one of the values `MSG_PERSISTENT` (default) or `MSG_BUFFERED`.

EnqOptions.transformation

  This read-write attribute specifies the name of the transformation that must be applied before the message is enqueued into the database. The transformation must be created using dbms_transform. The default is to have no transformation specified.

EnqOptions.visibility

  This read-write attribute specifies the transactional behavior of the enqueue request. It should be one of the values `ENQ_ON_COMMIT` (default) or `ENQ_IMMEDIATE`. Note the value of `autocommit` is ignored.

## 12.4. Message Properties

Note

These objects are used to identify the properties of messages that are enqueued and dequeued in queues. They are created by the method `Connection.msgproperties()`. They are used by the methods `Queue.enqone()` and `Queue.enqmany()` and returned by the methods `Queue.deqone()` and `Queue.deqmany()`.

MessageProperties.attempts

  This read-only attribute specifies the number of attempts that have been made to dequeue the message.

MessageProperties.correlation

  This read-write attribute specifies the correlation used when the message was enqueued.

MessageProperties.delay

  This read-write attribute specifies the number of seconds to delay an enqueued message. Any integer is acceptable but the constant `MSG_NO_DELAY` can also be used indicating that the message is available for immediate dequeuing.

MessageProperties.deliverymode

  This read-only attribute specifies the type of message that was dequeued. It will be one of the values `MSG_PERSISTENT` or `MSG_BUFFERED`.

MessageProperties.enqtime

  This read-only attribute specifies the time that the message was enqueued.

MessageProperties.exceptionq

  This read-write attribute specifies the name of the queue to which the message is moved if it cannot be processed successfully. Messages are moved if the number of unsuccessful dequeue attempts has exceeded the maximum number of retries or if the message has expired. All messages in the exception queue are in the `MSG_EXPIRED` state. The default value is the name of the exception queue associated with the queue table.

MessageProperties.expiration

  This read-write attribute specifies, in seconds, how long the message is available for dequeuing. This attribute is an offset from the delay attribute. Expiration processing requires the queue monitor to be running. Any integer is accepted but the constant `MSG_NO_EXPIRATION` can also be used indicating that the message never expires.

MessageProperties.msgid

  This read-only attribute specifies the id of the message in the last queue that enqueued or dequeued the message. If the message has never been dequeued or enqueued, the value will be None.

MessageProperties.payload

  This read-write attribute identifies the payload that will be enqueued or the payload that was dequeued when using a queue. When enqueuing, the value is checked to ensure that it conforms to the type expected by that queue. For RAW queues, the value can be a bytes object or a string. If the value is a string it will first be converted to bytes by encoding in the encoding identified by the attribute `Connection.encoding`.

MessageProperties.priority

  This read-write attribute specifies the priority of the message. A smaller number indicates a higher priority. The priority can be any integer, including negative numbers. The default value is zero.

MessageProperties.state

  This read-only attribute specifies the state of the message at the time of the dequeue. It will be one of the values `MSG_WAITING`, `MSG_READY`, `MSG_PROCESSED` or `MSG_EXPIRED`.

Messageproperties.recipient

  This read-write attribute specifies a list of recipient names that can be associated with a message at the time of enqueuing the message. This allows a limited set of recipients to dequeue each message. The recipient list associated with the message overrides the queue subscriber list, if there is one. The recipient names need not be in the subscriber list but can be, if desired.

  To dequeue a message, the consumername attribute can be set to one of the recipient names. The original message recipient list is not available on dequeued messages. All recipients have to dequeue a message before it gets removed from the queue.