Eventstore: Question: How can I get a list of all categories in GetEventStore?

[Narvalex]

Sorry if it is a stupid question. What I want is:

From streams like these:

• sales-sale102
• sales-sale103
• sales-sale104
• users-8989
• users-8990

Get somethig like this:
[ "sales", "users"]

I already asked this in the Google Groups and even in Stackoverflow, but with no response.

[nissbran]

It is possible to write a transient projection (Query), or a regular projection in EventStore. This might be a good starting point:

fromAll().
when({
    $init: function() {
        return {
            categories : []
        }
    },
    $any: function(s, e) {
        var category = e.streamId.split("-")[0];

        if (s.categories.includes(category))
            return;

        s.categories.push(category);
    }
})

[Narvalex]

I thought that there is a built-in thing like $ce-category. But thanks @nissbran!

[Narvalex]

Would it be faster to go fromStream('$streams') instead of going fromAll()?

[nissbran]

That is faster. Good idea :)

$ce-category just "groups" all events from the same category. So $ce-users will contain link events to all events in users streams. Its very useful for projections and when you want to create subscriptions that only target one aggregate root type.

[devcrafting]

Hi, I implemented the same projection, but having truncated events, these events do not have any streamId property. I can check if streamId is defined, but still if first event of all streams of a category have been truncated, I do not get the category in the projection.

I tried looking at event object for truncated events, everything is null or empty...but we can still see a Name (nothing else) when looking at $streams in the UI. Also, we can get the Name string with C# API, from ResolvedEvent.Event.Data. why is there nothing in parameters given to handle functions ?

Thanks for your feedbacks.

[devcrafting]

Hello, sorry I tried with fromStream('$streams')...it works with fromAll(). Still, I don't understand why there is some properties in events with fromAll and nothing with fromStream('$streams') ?
Also, looks like fromAll return only events from non system streams, right ? (a bit vague in doc "Selects events from the $allstream")
I would be happy to PR docs with answers :).