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Event store using PostgreSQL for persistence.
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Files
lib/event_store/storage/appender.ex
defmodule EventStore.Storage.Appender do
@moduledoc """
Append-only storage of events to a stream
"""
require Logger
alias EventStore.Sql.Statements
@doc """
Append the given list of events to storage
Returns `{:ok, event_ids}` on success, where `event_ids` is a list of the ids assigned by the database.
"""
def append(conn, events) do
execute_using_multirow_value_insert(conn, events)
end
defp execute_using_multirow_value_insert(conn, events) do
statement = build_insert_statement(events)
parameters = [length(events) | build_insert_parameters(events)]
conn
|> Postgrex.query(statement, parameters, pool: DBConnection.Poolboy)
|> handle_response(events)
end
defp build_insert_statement(events) do
Statements.create_events(length(events))
end
defp build_insert_parameters(events) do
events
|> Enum.with_index(1)
|> Enum.flat_map(fn {event, index} ->
[
index,
event.stream_id,
event.stream_version,
event.correlation_id,
event.causation_id,
event.event_type,
event.data,
event.metadata,
event.created_at,
]
end)
end
defp handle_response({:ok, %Postgrex.Result{num_rows: 0}}, []) do
_ = Logger.warn(fn -> "failed to append any events to stream" end)
{:ok, []}
end
defp handle_response({:ok, %Postgrex.Result{num_rows: 0}}, events) do
_ = Logger.warn(fn -> "failed to append any events to stream id #{stream_id(events)}" end)
{:error, :failed_to_append_events}
end
defp handle_response({:ok, %Postgrex.Result{num_rows: num_rows, rows: rows}}, events) do
event_ids = List.flatten(rows)
_ = Logger.info(fn -> "appended #{num_rows} event(s) to stream id #{stream_id(events)} (event ids: #{Enum.join(event_ids, ", ")})" end)
{:ok, event_ids}
end
defp handle_response({:error, %Postgrex.Error{postgres: %{code: :foreign_key_violation, message: message}}}, events) do
_ = Logger.warn(fn -> "failed to append events to stream id #{stream_id(events)} due to: #{inspect message}" end)
{:error, :stream_not_found}
end
defp handle_response({:error, %Postgrex.Error{postgres: %{code: :unique_violation, message: message}}}, events) do
_ = Logger.warn(fn -> "failed to append events to stream id #{stream_id(events)} due to: #{inspect message}" end)
{:error, :wrong_expected_version}
end
defp handle_response({:error, reason}, events) do
_ = Logger.warn(fn -> "failed to append events to stream id #{stream_id(events)} due to: #{inspect reason}" end)
{:error, reason}
end
defp stream_id([event | _]), do: event.stream_id
end