Fixed getting event #1

[noamkush]

While writing a storage backend for a document database, I tested DjangoModelStorage to understand the expected behavior and I noticed a bug with get_events when trying to get event with id 1. After appending the first event, it's impossible to get it as calling get_events(channel, 0) raises an exception while get_events(channel, 1) returns an empty list. See example code:

from django_eventstream.storage import DjangoModelStorage
storage = DjangoModelStorage()
channel = 'my_channel'

data = {'a': 'b'}
s.append_event(channel, 'message', data)
s.get_current_id(channel) # returns 1
s.get_events(channel, 0) # raises an exception
s.get_events(channel, 1) # returns []

I added basic tests for the DjangoModelStorage class and implemented the fix that's required according to my understanding of the expected behavior.

[jkarneges]

Hi! Indeed you are correct that the expected behavior of calling get_events(channel, 0) is to return events with IDs > 0.

However, errors may go undetected in the proposed fix. If rows are trimmed (via e.g. trim_event_log), then get_events may return items that don't directly follow last_id. This is why the original code looks up the previous event and then ensures it matches the first event returned in the filter call. I'll think about this some more...

[jkarneges]

Fixed this in f70108b4f42381dc775badf96d9b569d04c6cd72. This should ensure queries against ID 0 will work, while ensuring events aren't silently missed due to time trimming. I confirmed with your tests. Can you update this PR to include only the tests, and then I'll merge?

[noamkush]

Okay, you can now merge

[jkarneges]

Great. Thank you. :)