EventStore: Open-Source, Functional Database with Complex Event Processing in JS

Post by acemarke » Mon, Nov 05, 2018, 12:08 AM UTC

mattdeboard wrote: post #40

acemarke wrote: post #21

Earlier quoted context omitted.

Hi, I'm a Redux maintainer. Got any examples of this? Also, how do you feel it's better than a typical Redux app setup?

It seems like the main difference with a reducer is that the reducer just returns `state`, not `(state, action)`. I'm reading this for the first time but that's how I'm reading it. But y'all must be storing this `(point-in-time-state, action-that-produced-state)` somewhere, because the Redux Chrome plugin displays this data. Was I wrong in thinking the Chrome plugin was just visualizing data already stored by Redux?

    function createStore(reducer) {
        var state
        var listeners = []
        
        function getState() { return state  }
        
        function dispatch(action) {
            state = reducer(state, action)
            listeners.forEach(listener => listener())
        }
    }

Post by atoko » Mon, Nov 05, 2018, 12:49 AM UTC

arnioxux wrote: post #29

tobr wrote: post #16

I've played around recently with a Redux inspired frontend architecture where the complex, nested reducers are replaced with a single one that simply adds every action to an immutable linked list (i.e, `(state, action) => ({state, action})`. This means all the business logic that would normally live in reducers can be moved over to memoized selectors, which fixes the awkward difference in how reducers and selectors a…

I wrote a similar comment before, viewing redux as a realization of the event sourcing pattern: https://news.ycombinator.com/item?id=17061827 You can go even further and use the exact same "events" or "actions" for event sourcing on the server side too. You just need to save the list of actions to the server. This lets you do realtime sync and multiplayer really easily!

Post by manigandham » Mon, Nov 05, 2018, 4:03 AM UTC

root_axis wrote: post #34

stabbles wrote: post #31

Earlier quoted context omitted.

I've used a MySQL table `event_store` with fields `uuid`, `playhead`, `payload` and `recorded_on`; works fine.

How did you manage horizontal scaling with this approach?

Post by fulafel » Mon, Nov 05, 2018, 5:23 AM UTC

kyleperik wrote: post #11

lojack wrote: post #7

Earlier quoted context omitted.

It isn’t that contradictory. You can have data in a functional language. One of the common features of a functional language that separates it from imperative is data immutability. In this case it’s a database of immutable data. I personally understand exactly what they’re talking about when they call it a functional database.

I don't understand how this is useful. The purpose of functional programming isn't to make everything immutable, but to use immutability to prevent unnecessary change of state which can result in flaky code. So where's the usefulness in a functional Database? Also this still isn't functional. Is adding records to a set not mutation?

Post by rjbwork » Mon, Nov 05, 2018, 8:05 AM UTC

megakid wrote: post #9

We use this heavily in production and to good effect. It has its downsides (doesn't every product) but we have found it works well once you've grasped them. If you have a primarily .NET focused team, have plenty of event-driven applications and want to do CQRS / Event Sourcing for some of your applications I would recommend it as a starter step towards that. It gives you a lot 'out of the box' which is great when sta…