Documented how pymongo.monitoring can be used with MongoEngine

docs/guide/logging-monitoring.rst

@@ -0,0 +1,80 @@
+==================
+Logging/Monitoring
+==================
+
+It is possible to use `pymongo.monitoring <https://api.mongodb.com/python/current/api/pymongo/monitoring.html>`_ to monitor
+the driver events (e.g: queries, connections, etc). This can be handy if you want to monitor the queries issued by
+MongoEngine to the driver.
+
+To use `pymongo.monitoring` with MongoEngine, you need to make sure that you are registering the listeners
+**before** establishing the database connection (i.e calling `connect`):
+
+The following snippet provides a basic logging of all command events:
+
+.. code-block:: python
+
+    import logging
+    from pymongo import monitoring
+    from mongoengine import *
+
+    log = logging.getLogger()
+    log.setLevel(logging.DEBUG)
+    logging.basicConfig(level=logging.DEBUG)
+
+
+    class CommandLogger(monitoring.CommandListener):
+
+        def started(self, event):
+            log.debug("Command {0.command_name} with request id "
+                     "{0.request_id} started on server "
+                     "{0.connection_id}".format(event))
+
+        def succeeded(self, event):
+            log.debug("Command {0.command_name} with request id "
+                     "{0.request_id} on server {0.connection_id} "
+                     "succeeded in {0.duration_micros} "
+                     "microseconds".format(event))
+
+        def failed(self, event):
+            log.debug("Command {0.command_name} with request id "
+                     "{0.request_id} on server {0.connection_id} "
+                     "failed in {0.duration_micros} "
+                     "microseconds".format(event))
+
+    monitoring.register(CommandLogger())
+
+
+    class Jedi(Document):
+        name = StringField()
+
+
+    connect()
+
+
+    log.info('GO!')
+
+    log.info('Saving an item through MongoEngine...')
+    Jedi(name='Obi-Wan Kenobii').save()
+
+    log.info('Querying through MongoEngine...')
+    obiwan = Jedi.objects.first()
+
+    log.info('Updating through MongoEngine...')
+    obiwan.name = 'Obi-Wan Kenobi'
+    obiwan.save()
+
+
+Executing this prints the following output::
+
+    INFO:root:GO!
+    INFO:root:Saving an item through MongoEngine...
+    DEBUG:root:Command insert with request id 1681692777 started on server ('localhost', 27017)
+    DEBUG:root:Command insert with request id 1681692777 on server ('localhost', 27017) succeeded in 562 microseconds
+    INFO:root:Querying through MongoEngine...
+    DEBUG:root:Command find with request id 1714636915 started on server ('localhost', 27017)
+    DEBUG:root:Command find with request id 1714636915 on server ('localhost', 27017) succeeded in 341 microseconds
+    INFO:root:Updating through MongoEngine...
+    DEBUG:root:Command update with request id 1957747793 started on server ('localhost', 27017)
+    DEBUG:root:Command update with request id 1957747793 on server ('localhost', 27017) succeeded in 455 microseconds
+
+More details can of course be obtained by checking the `event` argument from the `CommandListener`.