Consumer Examples
=================
The following example illustrates a very simple consumer that simply logs each
message body as it's received.

.. code:: python

    from rejected import consumer
    import logging

    __version__ = '1.0.0'

    LOGGER = logging.getLogger(__name__)


    class ExampleConsumer(consumer.Consumer):

        def process(self):
            LOGGER.info(self.body)

All interaction with RabbitMQ with regard to connection management and message
handling, including acknowledgements and rejections are automatically handled
for you.

The ``__version__`` variable provides context in the rejected log files when
consumers are started and can be useful for investigating consumer behaviors in
production.

In this next example, a contrived ``ExampleConsumer._connect_to_database`` method
is added that will return ``False``. When ``ExampleConsumer.process`` evaluates
if it could connect to the database and finds it can not, it will raise a
:py:class:`rejected.consumer.ConsumerException` which will requeue the message
in RabbitMQ and increment an error counter. When too many errors occur, rejected
will automatically restart the consumer after a brief quiet period. For more
information on these exceptions, check out the :ref:`consumer API documentation <consumer_api>`.

.. code:: python

    from rejected import consumer
    import logging

    __version__ = '1.0.0'

    LOGGER = logging.getLogger(__name__)


    class ExampleConsumer(consumer.Consumer):

        def _connect_to_database(self):
            return False

        def process(self):
            if not self._connect_to_database:
                raise consumer.ConsumerException('Database error')

            LOGGER.info(self.body)

Some consumers are also publishers. In this next example, the message body will
be republished to a new exchange on the same RabbitMQ connection:

.. code:: python

    from rejected import consumer
    import logging

    __version__ = '1.0.0'

    LOGGER = logging.getLogger(__name__)


    class ExampleConsumer(consumer.PublishingConsumer):

        def process(self):
            LOGGER.info(self.body)
            self.publish('new-exchange', 'routing-key', {}, self.body)

Note that the previous example extends :py:class:`rejected.consumer.PublishingConsumer`
instead of :py:class:`rejected.consumer.Consumer`. For more information about what
base consumer classes exist, be sure to check out the :ref:`consumer API documentation <consumer_api>`.