EctoAutoMigrator

Ecto documentation proposes a way to run migrations outside of using mix here:

• https://hexdocs.pm/phoenix/releases.html#ecto-migrations-and-custom-commands

However, in a number of cases, eg whole system apps such as Nerves and the like, we actually want to run the migrations at app startup.

The solution to this is to create a genserver compatible module, which itself runs the migrations and we can then insert this into our children (just after we start the Repo perhaps) in application.ex (or wherever we start the repo)

However, we likely still want control over when we run the migrations, eg while developing some new migrations you don't want every invocation of mix running your migrations, nor watchers helpers, or editor plugins continuously causing the migrations to fire. So we conditionally run the migrations based on a config entry "run_migrations", which itself would be recommended to be set based on an environment variable

eg:

  config :my_app, run_migrations: System.get_env("RUN_MIGRATIONS")

To implement our module it should generally be sufficient to create a new Migrator module. Optionally any of the callback functions can be overridden, eg the original use case for this module was where the migrations absolutely must not fail. To achieve this a custom "migrate()" function could be used which performs some sensible recovery action on migration failure, eg destroying the database and migrating from scratch, or restoring a backup, or ignoring the migration and raising an error, etc.

eg it's often sufficient to do

defmodule MyApp.Repo.Migrator
  use Ecto.AutoMigrator
end

and then in application.ex add "MyApp.Repo.Migrator" to your list of children, somewhere after the Repo is started

Installation

If available in Hex, the package can be installed by adding ecto_auto_migrator to your list of dependencies in mix.exs:

def deps do
  [
    {:ecto_auto_migrator, "~> 0.1"}
  ]
end

Documentation can be generated with ExDoc and published on HexDocs. Once published, the docs can be found at https://hexdocs.pm/ecto_auto_migrator.