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Event store using PostgreSQL for persistence.
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lib/event_store/notifications/reader.ex
defmodule EventStore.Notifications.Reader do
@moduledoc false
# Reads events from storage by each event number range received.
use GenStage
alias EventStore.Notifications.Listener
alias EventStore.{RecordedEvent, Storage}
@conn EventStore.Notifications.Reader.Postgrex
def start_link(serializer) do
GenStage.start_link(__MODULE__, serializer, name: __MODULE__)
end
# Starts a permanent subscription to the listener producer stage which will
# automatically start requesting items.
def init(serializer) do
opts = [
dispatcher: GenStage.BroadcastDispatcher,
subscribe_to: [{Listener, max_demand: 1}]
]
{:producer_consumer, serializer, opts}
end
# Fetch events from storage and pass onwards to subscibers
def handle_events(events, _from, state) do
stream_events =
Enum.map(events, fn {stream_uuid, stream_id, first_stream_version, last_stream_version} ->
read_events(stream_uuid, stream_id, first_stream_version, last_stream_version, state)
end)
{:noreply, stream_events, state}
end
defp read_events(stream_uuid, stream_id, from_stream_version, to_stream_version, serializer) do
count = to_stream_version - from_stream_version + 1
with {:ok, events} <-
Storage.read_stream_forward(@conn, stream_id, from_stream_version, count),
deserialized_events <- deserialize_recorded_events(events, serializer) do
{stream_uuid, deserialized_events}
end
end
defp deserialize_recorded_events(recorded_events, serializer) do
Enum.map(recorded_events, &RecordedEvent.deserialize(&1, serializer))
end
end