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Event store using PostgreSQL for persistence.
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lib/event_store/storage/stream.ex
defmodule EventStore.Storage.Stream do
@moduledoc """
Streams are an abstraction around a stream of events for a given stream identity
"""
require Logger
alias EventStore.Sql.Statements
alias EventStore.Storage.{Appender,Reader,Stream}
def append_to_stream(conn, stream_uuid, expected_version, events) when expected_version == 0 do
case create_stream(conn, stream_uuid) do
{:ok, stream_id} -> Appender.append(conn, stream_id, expected_version, events)
response -> response
end
end
def append_to_stream(conn, stream_uuid, expected_version, events) when expected_version > 0 do
execute_with_stream_id(conn, stream_uuid, fn stream_id ->
Appender.append(conn, stream_id, expected_version, events)
end)
end
def read_stream_forward(conn, stream_uuid, start_version, count \\ nil) do
execute_with_stream_id(conn, stream_uuid, fn stream_id ->
Reader.read_forward(conn, stream_id, start_version, count)
end)
end
def read_all_streams_forward(conn, start_event_id, count \\ nil) do
Reader.read_all_forward(conn, start_event_id, count)
end
def latest_event_id(conn) do
Stream.Query.execute(conn)
end
defp execute_with_stream_id(conn, stream_uuid, execute_fn) do
case lookup_stream_id(conn, stream_uuid) do
{:ok, stream_id} -> execute_fn.(stream_id)
response -> response
end
end
defp create_stream(conn, stream_uuid) do
Logger.debug "attempting to create stream #{stream_uuid}"
conn
|> Postgrex.query(Statements.create_stream, [stream_uuid, "default"])
|> handle_create_response(stream_uuid)
end
defp handle_create_response({:ok, %Postgrex.Result{rows: [[stream_id]]}}, stream_uuid) do
Logger.debug "created stream #{stream_uuid} with id #{stream_id}"
{:ok, stream_id}
end
defp handle_create_response({:error, %Postgrex.Error{postgres: %{constraint: "ix_streams_stream_uuid"}}}, stream_uuid) do
Logger.warn "failed to create stream #{stream_uuid}, already exists"
{:error, :wrong_expected_version}
end
defp handle_create_response({:error, error}, stream_uuid) do
Logger.warn "failed to create stream #{stream_uuid}"
{:error, error}
end
defp lookup_stream_id(conn, stream_uuid) do
conn
|> Postgrex.query(Statements.query_stream_id, [stream_uuid])
|> handle_lookup_response(stream_uuid)
end
defp handle_lookup_response({:ok, %Postgrex.Result{num_rows: 0}}, stream_uuid) do
Logger.warn("attempted to access unknown stream #{stream_uuid}")
{:error, :stream_not_found}
end
defp handle_lookup_response({:ok, %Postgrex.Result{rows: [[stream_id]]}}, _) do
{:ok, stream_id}
end
defmodule Query do
def execute(conn) do
conn
|> Postgrex.query(Statements.query_latest_event_id, [])
|> handle_response
end
defp handle_response({:ok, %Postgrex.Result{num_rows: 0}}) do
{:ok, 0}
end
defp handle_response({:ok, %Postgrex.Result{rows: [[event_id]]}}) do
{:ok, event_id}
end
end
end