How to use Greg’s Event Store from ruby

I one of a previous blog’s post I mentioned that we have to create a some tool to communicate with Greg’s ES. We did it. We created HttpEventstore gem which is a HTTP connector to the Greg’s Event Store. The reason of creating such tool was that in our projects we already use Event Sourcing and we experiment with Greg’s tool.

How to use it

To communicate with ES you have to create instance of HttpEventstore::Connection class. After configuring a client, you can do the following things.

client = HttpEventstore::Connection.new do |config|
   #default value is '127.0.0.1'
   config.endpoint = 'your_endpoint'
   #default value is 2113
   config.port = 'your_port'
   #default value is 20 entries per page
   config.page_size = 'your_page_size'
end

Creating new event

Creating a single event:

stream_name = "order_1"
event_data = { event_type: "OrderCreated",
               data: { data: "sample" },
               event_id: "b2d506fd-409d-4ec7-b02f-c6d2295c7edd" }
client.append_to_stream(stream_name, event_data)

EventData = Struct.new(:data, :event_type)
stream_name = "order_1"
event_data = EventData.new({ data: "sample" }, "OrderCreated")
client.append_to_stream(stream_name, event_data)

You can pass event’s data as a Hash or Struct. As you can see in above example event_id is optional parameter. If you don’t set it we will generate it for you.

Creating a single event with optimistic locking:

stream_name = "order_1"
event_data = { event_type: "OrderCreated", data: { data: "sample" }}
expected_version = 1
client.append_to_stream(stream_name, event_data, expected_version)

The expected version is a number representing the version of the stream. It is a next expected identifier of event. So, if your last event’s position id is equal 40 that expected_version will be 41.

Deleting stream

The soft delete cause that you will be allowed to recreate the stream by creating new event. If you recreate soft deleted stream all events are lost. After an hard delete any try to load the stream or create event will result in a 410 response.

The soft delete of single stream:

stream_name = "order_1"
client.delete_stream("stream_name")

The hard delete of single stream:

stream_name = "order_1"
hard_delete = true
client.delete_stream("stream_name", hard_delete)

Reading stream’s event forward

Reading stream forward without Long Pooling

stream_name = "order_1"
start = 21
count = 40
client.read_events_forward(stream_name, start, count)

Reading stream forward using Long Pooling

stream_name = "order_1"
start = 21
count = 40
pool_time = 15
client.read_events_forward(stream_name, start, count, poll_time)

Long Pooling in ES works as when you want to load head of stream and no data is available the server will wait specified amount of time. So, if you want to fetch the a newest entries you can specify pool_time attribute to wait before returning with no result. The pool_time is time in seconds.

Reading stream’s event backward

stream_name = "order_1"
start = 21
count = 40
client.read_events_backward(stream_name, start, count)

Reading all stream’s event forward

stream_name = "order_1"
client.read_all_events_forward(stream_name)

This method allows us to load all stream’s events ascending.

Reading all stream’s event backward

stream_name = "order_1"
client.read_all_events_backward(stream_name)

This method allows us to load all stream’s events descending.

Example

One of my teammates has created sample application which uses Greg’s Event Store and our gem. You can find out it here. This project represents example of rails app based on CQRS/ES architecture.

How to use Greg's Event Store from ruby