Pushing data into streams in the EventStore

I'm playing with the EventStore and I need to push some data into it in the form of streams.

What does this look like? Well I'm using NodeJS, and naturally that means using JSON and object literals:

So, if I have an event

// An Event
{
  Data: {
    PonyName: "Rainbow Dash",
    TrampStamp: "Rainbow",
    Date: "January 2013"
  },
  EventType: "PonyBorn"
}

And I want to get this into a stream, well first I want to package it up

// A package with the event in it
{
  CorrelationId: "something-i-know",
  ExpectedVersion: "last-version-i-knew-about",
  Events: [ ev ]
}

And serialise it

var body = JSON.stringify(package)

I can POST it to the event store with the following code

var req = http.request({
  host: "127.0.0.1",
  port: 2113,
  path: "/streams/ponies",
  method: "POST",
  headers: {
    "Accept": "application/json",
    "Content-Type": "application/json",
    "Content-Length": body.length
  }
}, function(res) {
  // Handle this
})

req.write(body)
req.end()

What do we notice about the data?

• We can supply a correlation id for our own convenience
• We supply an expected version so our event can be rejected if things are not as they should be
• We can send a collection of events to be committed all as one
• EventType can be sent in alongside the event data

And what do we notice about the request?

• We choose which stream to post to as part of the URL
• We specify the content types we expect and are sending (because it can accept XML etc)

What happens once I've done this?

Well, we'll see that I have a ponies stream

/streams

{
  title: "ponies",
  uri: "http://127.0.0.1:2113/streams/ponies",
  accepts: [
    {
      type: "text/xml"
    },
    {
      type: "application/atom+xml"
    },
    {
      type: "application/json"
    },
    {
      type: "application/atom+x.json"
    }
  ]
},

And that if we go to this ponies stream via the URI specified we'll see

/streams/ponies

[
  {
    title: "ponies #1",
    id: "http://127.0.0.1:2113/streams/ponies/1",
    updated: "2013-03-01T22:30:11.790066Z",
    author: {
      name: "EventStore"
    },
    summary: "Entry #1",
    links: [
      {
        uri: "http://127.0.0.1:2113/streams/ponies/1",
        relation: "edit"
      },
      {
        uri: "http://127.0.0.1:2113/streams/ponies/event/1?format=text",
        type: "text/plain"
      },
      {
        uri: "http://127.0.0.1:2113/streams/ponies/event/1?format=json",
        relation: "alternate",
        type: "application/json"
      },
      {
        uri: "http://127.0.0.1:2113/streams/ponies/event/1?format=xml",
        relation: "alternate",
        type: "text/xml"
      }
    ]
  },
  {
    title: "ponies #0",
    id: "http://127.0.0.1:2113/streams/ponies/0",
    updated: "2013-03-01T22:30:11.79004Z",
    author: {
      name: "EventStore"
    },
    summary: "Entry #0",
    links: [
      {
        uri: "http://127.0.0.1:2113/streams/ponies/0",
        relation: "edit"
      },
      {
        uri: "http://127.0.0.1:2113/streams/ponies/event/0?format=text",
        type: "text/plain"
      },
      {
        uri: "http://127.0.0.1:2113/streams/ponies/event/0?format=json",
        relation: "alternate",
        type: "application/json"
      },
      {
        uri: "http://127.0.0.1:2113/streams/ponies/event/0?format=xml",
        relation: "alternate",
        type: "text/xml"
      }
    ]
  }
]

We have two events, navigating to them we can see that one of them is for the creation of the stream

/streams/ponies/event/0?format=json

{
  eventStreamId: "ponies",
  eventNumber: 0,
  eventType: "$stream-created-implicit",
  data: "",
  metadata: ""
}

And the other one is the event we pushed

/streams/ponies/event/1?format=json

{
  eventStreamId: "ponies",
  eventNumber: 1,
  eventType: "PonyBorn",
  data: {
    PonyName: "Rainbow Dash",
    TrampStamp: "Rainbow",
    Date: "January 2013"
  },
  metadata: ""
}

Neato, I guess we notice a few things here then

• The stream doesn't contain the actual events, just links to the events
• The stream is pageable, and contains the links to the pages (well, it's AtomPub)
• Each event has its own unique uri, because events are immutable these can be cached by any intermdiate proxy

And indeed, if we look at the header on a HTTP request for one of these events we'll see

Cache-Control:max-age=31556926

That's cool, we've discovered that

• We can throw events into the event store with a default partitioning (the stream name specified)
• We can get them back out again by paging through the links in that stream
• Events are infinitely cacheable
• Everything is AtomPub
• Everything is easily navigable

Now, if we were building a standard event sourced model we'd be able to page through these streams to build up our snapshots/viewmodels and that's all very neat and tidy and that would be the end of our story.

Next up however, it's more interesting to go and have a look at projections now, and see what questions we can ask of those streams in the event store itself.