Allin

Example application how to use a single Ecto Repo that supports multiple DB engines.

Features:

• uses MaxoAdapt for dynamic DB adapter switching + great dev experience
• seamless runtime switching between DB engines possible, while still using the same main Repo module
• support for database-specific migrations, when needed
• migrations for all databases are kept together, to simplify code reuse as much as possible
• same ExUnit tests can be run for different DB engines via ENV variable switch
• Mix Ecto commands work as usual

Setup

Please start postgres / mysql with the included docker-compose file!

$ docker compose up

Now try the Elixir app without any options:

$ iex -S mix
** (Mix) Could not start application allin: exited in: Allin.Application.start(:normal, [])
    ** (EXIT) an exception was raised:
        ** (RuntimeError) PLEASE PROVIDE `DBTYPE` ENV variable - psql / mysql / sqlite!
            (allin 0.1.0) lib/allin/setup.ex:13: Allin.Setup.assert_correct_db_type!/0
            (allin 0.1.0) lib/allin/setup.ex:18: Allin.Setup.setup_repo!/0
            (allin 0.1.0) lib/allin/application.ex:8: Allin.Application.start/2
            (kernel 8.5.3) application_master.erl:293: :application_master.start_it_old/4

It fails, because we did not provide the desired DB type to be configured. Let's do it now:

With SQLITE:

$ DBTYPE=sqlite iex -S mix
iex(1)> Allin.Repo.query("select 2 + 2")
{:ok,
 %Exqlite.Result{
   command: :execute,
   columns: ["2 + 2"],
   rows: [[4]],
   num_rows: 1
 }}

With MySQL:

$ DBTYPE=mysql iex -S mix
iex(1)> Allin.Repo.query("select 2 + 2")
{:ok,
 %MyXQL.Result{
   columns: ["2 + 2"],
   connection_id: 109,
   last_insert_id: nil,
   num_rows: 1,
   rows: [[4]],
   num_warnings: 0
 }}

And with Postgres

$ DBTYPE=psql iex -S mix
iex(1)> Allin.Repo.query("select 2 + 2")
{:ok,
 %Postgrex.Result{
   command: :select,
   columns: ["?column?"],
   rows: [[4]],
   num_rows: 1,
   connection_id: 779,
   messages: []
 }}

Enjoy! 💜

Details

• Allin.Repos.Setup

  • single module to contain most of the logic for (re-) configuration of repos

  • Allin.Repos.Setup.setup_repo!(true)

    • used in mix tasks to start the rep

  • Allin.Repos.Setup.setup_env()

    • used in config/runtime.exs to configure the :ecto_repos list dynamically
    • is also ran on any live re-configuration of the repo

  • Allin.Repos.Setup.to_mysql()

    • runtime switching to MySQL DB

  • Allin.Repos.Setup.to_psql()

    • runtime switching to Postgres DB

  • Allin.Repos.Setup.to_sqlite()

    • runtime switching to Sqlite DB

• Allin.Repos.RepoSupervisor

  • dynamic supervisor for repositories
  • allows clean switching between different DB-specific adapter repos
  • starting and stopping them accordingly

• mix app.config (used in mix.exs / aliases)

  • needed to make config/runtime.exs work with Repo config for Mix tasks
  • https://elixirforum.com/t/config-runtime-exs-not-loaded-on-mix-tasks/38034