We recently introduced a new feature in autoki called the social feed. It’s basically a yellow box displaying any events on the platform relevant to the current user, like a friend has posted a new photo, or a new interesting car was uploaded. The data model behind this is pretty straightforward, we have a FeedEvent class and all kinds of subclasses, e.g. a MessageReceivedEvent. Each event belongs to a user and an event source, in this example the user would be the user who received the message and the event source would be the message itself. For each user, we simply display all the events that belong to him or her.

Now the question was this: How do we create these events? The most straightforward way would probably have been to create them in the models, so the Message model would have an after_create callback that created the event. What we didn’t like about this solution was that we would put a whole bunch of logic into the models that didn’t really belong there. Why would a Message care if there was some kind of event feed? Plus these events would be all around in our unit tests and make the bloated and probably sloooow (again). So we wanted to use the observer pattern to remove the creation of the event from the models.

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