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Event store using PostgreSQL for persistence.
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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 the given stream.
Returns `{:ok, count}` on success, where count indicates the number of appended events.
"""
def append(conn, stream_id, events) do
execute_using_multirow_value_insert(conn, stream_id, events)
end
defp execute_using_multirow_value_insert(conn, stream_id, events) do
statement = build_insert_statement(events)
parameters = build_insert_parameters(events)
conn
|> Postgrex.query(statement, parameters)
|> handle_response(stream_id)
end
defp build_insert_statement(events) do
Statements.create_events(length(events))
end
defp build_insert_parameters(events) do
events
|> Enum.map(fn(event) ->
[
event.event_id,
event.stream_id,
event.stream_version,
event.correlation_id,
event.event_type,
event.data,
event.metadata
]
end)
|> List.flatten
end
defp handle_response({:ok, %Postgrex.Result{num_rows: 0}}, stream_id) do
Logger.info(fn -> "failed to append any events to stream id #{stream_id}" end)
{:ok, 0}
end
defp handle_response({:ok, %Postgrex.Result{num_rows: num_rows}}, stream_id) do
Logger.info(fn -> "appended #{num_rows} events to stream id #{stream_id}" end)
{:ok, num_rows}
end
defp handle_response({:error, %Postgrex.Error{postgres: %{code: :foreign_key_violation, message: message}}}, stream_id) do
Logger.warn(fn -> "failed to append events to stream id #{stream_id} due to: #{inspect message}" end)
{:error, :stream_not_found}
end
defp handle_response({:error, %Postgrex.Error{postgres: %{code: :unique_violation, message: message}}}, stream_id) do
Logger.warn(fn -> "failed to append events to stream id #{stream_id} due to: #{inspect message}" end)
{:error, :wrong_expected_version}
end
defp handle_response({:error, reason}, stream_id) do
Logger.warn(fn -> "failed to append events to stream id #{stream_id} due to: #{inspect reason}" end)
{:error, reason}
end
end