Getting the original stream from events projected by $stream_by_category

[Arno den Uijl]

Hi,

I've found some posts regarding the $stream_by_category projection but I haven't been able to answer my question with these.

I have a bunch of streams in a category name connection. Now I want to get all the streams in that category. If I understand correct the $stream_by_category projection should create a stream named $category-connection that links all the first events in all the connection-* streams.

If I look in the $category-connection stream i see entries, but I have no idea how to get to the original source stream.

If I use the .Net client I both OriginalStreamId and Event.EventStreamId are "$category-connection" and I see no reference to the original connectoin-xxxx stream. Even if i set resolveLinkTos to true (I use ReadStreamEventsForwardAsync).

If i do a request on the HTTP api I see the following entries:

http://127.0.0.1:2113/streams/$category-connection
Accept:application/vnd.eventstore.atom+json
ES-ResolveLinkTo:true

    "entries": [
        {
            "title": "393221@$category-connection",
            "id": "http://127.0.0.1:2113/streams/%24category-connection/393221",
            "updated": "2018-05-22T08:04:59.738933Z",
            "author": {
                "name": "EventStore"
            },
            "summary": "$@",
            "links": [
                {
                    "uri": "http://127.0.0.1:2113/streams/%24category-connection/393221",
                    "relation": "edit"
                },
                {
                    "uri": "http://127.0.0.1:2113/streams/%24category-connection/393221",
                    "relation": "alternate"
                }
            ]
        }

How do I find a reference to the connection-xxxxx stream this?

kind regards,

Arno

[Greg Young]

The payload of the link event is $>1234@streamname  if you look. I believe this is also surfaced in the API but don't remember off the top of my head where (I will look through the api in a bit).

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[Arno den Uijl]

If I request a single event with embed=body I get the following. Hould it be in here?:

http://127.0.0.1:2113/streams/%24category-connection/9237?embed=body

{
    "eventId": "42f7d4f8-f49f-4e8b-a901-af5a405f92ae",
    "eventType": "$@",
    "eventNumber": 9237,
    "metaData": "{\"$v\":\"4:-1:1:3\",\"$c\":858258872,\"$p\":858258872,\"$causedBy\":\"0c480f70-acca-4af2-bd41-bdf4c3c5a7b2\"}",
    "streamId": "$category-connection",
    "isJson": false,
    "isMetaData": true,
    "isLinkMetaData": false,
    "positionEventNumber": 9237,
    "positionStreamId": "$category-connection",
    "title": "9237@$category-connection",
    "id": "http://127.0.0.1:2113/streams/%24category-connection/9237",
    "updated": "2018-05-22T12:12:34.823235Z",

    "author": {
        "name": "EventStore"
    },
    "summary": "$@",
    "links": [
        {

            "uri": "http://127.0.0.1:2113/streams/%24category-connection/9237",
            "relation": "edit"
        },
        {
            "uri": "http://127.0.0.1:2113/streams/%24category-connection/9237",
            "relation": "alternate"
        }
    ]
}

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[Arno den Uijl]

Thanks for the hint Greg. It indeed is in the payload (data).

I was able to get it out with:

Encoding.UTF8.GetString(e.Event.Data)

It's so simple once you know it. I was so used to events and links to events that I never realised there is something like a 'StreamReference' and that it is a bit different than a normal link event. I was just trying to get it out with 'e.OriginalStreamId' or 'e.Event.EventStreamId' and with resolveLinkTos to false and true.

Why isn't it 'just' a link event like in the '$ce-xxxx' streams? I think what would make it simpler. (i have just a basic understanding of how the eventstore works, so this might be weird thing to suggest.)