Ecto Release Migrations

Ecto Release Migrations Setup

Overview

In Elixir releases, Mix is not available. This skill creates a Release module that handles database creation, migration, and rollback via bin/app_name eval commands.

Workflow

1. Detect app name and repos

   • Check mix.exs for app name
   • Check config/config.exs or config/runtime.exs for Ecto repos

2. Create Release module

   • Location: lib/<app_name>/release.ex
   • Must handle multiple repos if present

3. Verify config

   • Ensure config/runtime.exs has production database config
   • Check for DATABASE_URL or explicit config

Implementation

Release Module Template

defmodule <AppName>.Release do
  @moduledoc """
  Release tasks for database management.
  
  Usage in production:
    bin/<app_name> eval "<AppName>.Release.migrate()"
    bin/<app_name> eval "<AppName>.Release.rollback(<AppName>.Repo, 20240101000000)"
  """

  @app :<app_name>

  def migrate do
    load_app()

    for repo <- repos() do
      {:ok, _, _} = Ecto.Migrator.with_repo(repo, &Ecto.Migrator.run(&1, :up, all: true))
    end
  end

  def rollback(repo, version) do
    load_app()
    {:ok, _, _} = Ecto.Migrator.with_repo(repo, &Ecto.Migrator.run(&1, :down, to: version))
  end

  def create do
    load_app()

    for repo <- repos() do
      case repo.__adapter__().storage_up(repo.config()) do
        :ok -> IO.puts("Database created for #{inspect(repo)}")
        {:error, :already_up} -> IO.puts("Database already exists for #{inspect(repo)}")
        {:error, term} -> raise "Failed to create database: #{inspect(term)}"
      end
    end
  end

  def seed do
    load_app()
    
    for repo <- repos() do
      {:ok, _, _} = Ecto.Migrator.with_repo(repo, fn _repo ->
        seed_file = Application.app_dir(@app, "priv/repo/seeds.exs")
        if File.exists?(seed_file) do
          Code.eval_file(seed_file)
        end
      end)
    end
  end

  defp repos do
    Application.fetch_env!(@app, :ecto_repos)
  end

  defp load_app do
    Application.ensure_all_started(:ssl)
    Application.load(@app)
  end
end

For Phoenix Projects with Multiple Repos

If multiple repos exist (e.g., Repo and ReadRepo), ensure config.exs has:

config :<app_name>, ecto_repos: [<AppName>.Repo, <AppName>.ReadRepo]

Verification Steps

After creating the module:

1. Compile: mix compile
2. Test locally: mix run -e "<AppName>.Release.migrate()"
3. Build release: MIX_ENV=prod mix release
4. Test release: _build/prod/rel/<app_name>/bin/<app_name> eval "<AppName>.Release.migrate()"

Usage Documentation

Add to project README or deployment docs:

# Create database (first deploy only)
bin/<app_name> eval "<AppName>.Release.migrate()"

# Run migrations
bin/<app_name> eval "<AppName>.Release.migrate()"

# Rollback to specific version
bin/<app_name> eval "<AppName>.Release.rollback(<AppName>.Repo, 20240101000000)"

# Seed database
bin/<app_name> eval "<AppName>.Release.seed()"

Common Issues

• SSL not started: Ensure Application.ensure_all_started(:ssl) is called before repo operations
• App not loaded: Always call Application.load(@app) first
• Missing ecto_repos config: Verify config :app_name, ecto_repos: [...] exists