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Event store using PostgreSQL for persistence.
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lib/event_store/storage/reader.ex
defmodule EventStore.Storage.Reader do
@moduledoc """
Reads events for a given stream identity
"""
require Logger
alias EventStore.RecordedEvent
alias EventStore.Sql.Statements
alias EventStore.Storage.Reader
@doc """
Read events appended to a single stream forward from the given starting version
"""
def read_forward(conn, stream_id, start_version, count) do
case Reader.Query.read_events_forward(conn, stream_id, start_version, count) do
{:ok, []} = reply -> reply
{:ok, rows} -> map_rows_to_event_data(rows)
{:error, reason} -> failed_to_read(stream_id, reason)
end
end
@doc """
Read events appended to all streams forward from the given start event id inclusive
"""
def read_all_forward(conn, start_event_id, count) do
case Reader.Query.read_all_events_forward(conn, start_event_id, count) do
{:ok, []} = reply -> reply
{:ok, rows} -> map_rows_to_event_data(rows)
{:error, reason} -> failed_to_read_all_stream(reason)
end
end
defp map_rows_to_event_data(rows) do
{:ok, Reader.EventAdapter.to_event_data(rows)}
end
defp failed_to_read(stream_id, reason) do
_ = Logger.warn(fn -> "failed to read events from stream id #{stream_id} due to #{inspect reason}" end)
{:error, reason}
end
defp failed_to_read_all_stream(reason) do
_ = Logger.warn(fn -> "failed to read events from all streams due to #{inspect reason}" end)
{:error, reason}
end
defmodule EventAdapter do
@moduledoc """
Map event data from the database to `RecordedEvent` struct
"""
def to_event_data(rows) do
rows
|> Enum.map(&to_event_data_from_row/1)
end
def to_event_data_from_row([event_id, stream_id, stream_version, event_type, correlation_id, data, metadata, created_at]) do
%RecordedEvent{
event_id: event_id,
stream_id: stream_id,
stream_version: stream_version,
event_type: event_type,
correlation_id: correlation_id,
data: data,
metadata: metadata,
created_at: created_at
}
end
end
defmodule Query do
def read_events_forward(conn, stream_id, start_version, count) do
conn
|> Postgrex.query(Statements.read_events_forward, [stream_id, start_version, count])
|> handle_response
end
def read_all_events_forward(conn, start_event_id, count) do
conn
|> Postgrex.query(Statements.read_all_events_forward, [start_event_id, count])
|> handle_response
end
defp handle_response({:ok, %Postgrex.Result{num_rows: 0}}) do
{:ok, []}
end
defp handle_response({:ok, %Postgrex.Result{rows: rows}}) do
{:ok, rows}
end
defp handle_response({:error, %Postgrex.Error{postgres: %{message: reason}}}) do
_ = Logger.warn(fn -> "failed to read events from stream due to: #{inspect reason}" end)
{:error, reason}
end
end
end