alog

alog (Append-only Log) is an easy way to start using the Lambda/Kappa architecture in your Elixir/Phoenix Apps while still using PostgreSQL (with Ecto).

This module provides some helper functions to make it easy to insert and retrieve the data you need.

Usage

At the top of the schema you wish to use append only functions for, use this module:

use Alog

The append only functions will then be available to call as part of your schema.

Example

defmodule MyApp.User do
  use Ecto.Schema
  use Alog

  import Ecto.Changeset

  schema "users" do
    ...
  end

  def changeset(user, attrs) do
    ...
  end
end

Repo

You can set the repo you want Alog to use in a config file:

config :alog, Alog,
  repo: MyApp.Repo

If you do not explicitly set a Repo, Alog will try to find it using your application name. So if your app is MyApp and your schema is MyApp.User, or MyApp.Accounts.User, your Repo should be MyApp.Repo.

Uniqueness

Due to the append only manner in which Alog stores data, it is not compatible with tables that have Unique Indexes applied to any of their columns. If you wish to use alog, you will have to remove these indexes.

For example, the following in a migration file would remove a unique index on the email column from the users table.

drop(unique_index(:users, :email))

See https://hexdocs.pm/ecto_sql/Ecto.Migration.html#content for more details.

If you want to ensure each entry in your database has a unique field, you can use the Ecto.Changeset.unique_constraint/3 function as normal, and Alog will ensure there are no repeated fields, other than those of the same entry, returning an invalid changeset if there are.