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Event store using PostgreSQL for persistence.
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lib/event_store/streams/stream.ex
defmodule EventStore.Streams.Stream do
@moduledoc """
An event stream
"""
use GenServer
require Logger
alias EventStore.{Storage,Writer}
alias EventStore.Streams.Stream
defstruct stream_uuid: nil, stream_id: nil, stream_version: 0
def start_link(stream_uuid) do
GenServer.start_link(__MODULE__, %Stream{stream_uuid: stream_uuid})
end
@doc """
Append the given list of events to the stream, expected version is used for optimistic concurrency
Each logical stream is a separate process; writes to a single stream will always be serialized.
"""
def append_to_stream(stream, expected_version, events) do
GenServer.call(stream, {:append_to_stream, expected_version, events})
end
def init(%Stream{stream_uuid: stream_uuid} = state) do
GenServer.cast(self, {:open_stream, stream_uuid})
{:ok, state}
end
def handle_cast({:open_stream, stream_uuid}, %Stream{} = state) do
{:ok, stream_id, stream_version} = Storage.stream_info(stream_uuid)
state = %Stream{state | stream_id: stream_id, stream_version: stream_version}
{:noreply, state}
end
def handle_call({:append_to_stream, expected_version, events}, _from, %Stream{stream_version: stream_version} = state) do
{:ok, state, persisted_events} = append_to_storage(expected_version, events, state)
state = %Stream{state | stream_version: stream_version + length(persisted_events)}
{:reply, {:ok, persisted_events}, state}
end
defp append_to_storage(expected_version, events, %Stream{stream_uuid: stream_uuid, stream_id: stream_id, stream_version: stream_version} = state) when expected_version == 0 and is_nil(stream_id) and stream_version == 0 do
with {:ok, stream_id} <- Storage.create_stream(stream_uuid),
{:ok, persisted_events} <- Writer.append_to_stream(events, stream_uuid, stream_id, stream_version),
do: {:ok, %Stream{state | stream_id: stream_id}, persisted_events}
end
defp append_to_storage(expected_version, events, %Stream{stream_uuid: stream_uuid, stream_id: stream_id, stream_version: stream_version} = state) when expected_version > 0 and not is_nil(stream_id) and stream_version == expected_version do
{:ok, persisted_events} = Writer.append_to_stream(events, stream_uuid, stream_id, stream_version)
{:ok, state, persisted_events}
end
defp append_to_storage(_expected_version, _events, _state) do
{:error, :wrong_expected_version}
end
end