# RailwayIpc

The purpose of Railway is to standardize a common set of API's and procedures for dealing with inter-process communication between applications via RabbitMQ. This projects implements the API's and procedures for Elixir based projects.

## Installation

If [available in Hex](https://hex.pm/docs/publish), the package can be installed by adding `railway_ipc` to your list of dependencies in `mix.exs`:

```elixir
def deps do
  [
    {:railway_ipc, "~> 0.3.2"}
  ]
end
```

## Getting Started

Configure Railway to work with your Repo. Add the following to your `config/config.exs`:

```elixir
config :railway_ipc,
  repo: ApplicationName.Repo
```

Run the mix task to generate the migrations to add the published messages and consumed messages tables to your app's DB:

```bash
mix railway_ipc.generate_migrations ./path/to/migration/directory
mix ecto.migrate
```

> Note: Path to migration directory defaults to `./priv/repo/migrations` if none is passed in.

**If there are issues running the migration or deploying the migration, try manually writing the name of the migration module (not the file) to avoid using interpolation.**

Documentation can be generated with [ExDoc](https://github.com/elixir-lang/ex_doc) and published on [HexDocs](https://hexdocs.pm).
Once published, the docs can be found at [https://hexdocs.pm/railway_ipc](https://hexdocs.pm/railway_ipc).

## Consuming the same message on multiple queues

Out of the box, Railway can handle storing the same messages multiple times if it's consumed on multiple queues. If you are upgrading Railway from 2.1 or earlier, you will need to run the following migration to make `uuid` and `queue` a combined primary key for the consumed messages table.

```elixir
defmodule YOUR_APP_NAME_HERE.Repo.Migrations.UpdateRailwayMessagePKey do
  use Ecto.Migration

  import Ecto.Query, only: [from: 2]
  alias Registrar.Repo

  def up do
    alter table(:railway_ipc_consumed_messages) do
      add :new_uuid, :uuid
    end

    flush()

    from(m in "railway_ipc_consumed_messages", update: [set: [new_uuid: m.uuid]])
    |> Repo.update_all([])

    alter table(:railway_ipc_consumed_messages) do
      remove :uuid
      modify :queue, :string, primary_key: true, null: false
      modify :new_uuid, :uuid, primary_key: true, null: false
    end

    rename(table(:railway_ipc_consumed_messages), :new_uuid, to: :uuid)

    create unique_index(
      "railway_ipc_consumed_messages",
      [:uuid, :queue],
      name: :railway_ipc_consumed_messages_uniqueness_index
    )
  end

  def down do
    alter table(:railway_ipc_consumed_messages) do
      add :old_uuid, :uuid
      add :old_queue, :string
    end

    flush()

    from(m in "railway_ipc_consumed_messages", update: [set: [old_uuid: m.uuid, old_queue: m.queue]])
    |> Repo.update_all([])

    alter table(:railway_ipc_consumed_messages) do
      remove :uuid
      remove :queue
      modify :old_uuid, :uuid, primary_key: true, null: false
      modify :old_queue, :string, null: false
    end

    rename(table(:railway_ipc_consumed_messages), :old_uuid, to: :uuid)
    rename(table(:railway_ipc_consumed_messages), :old_queue, to: :queue)
  end
end
```

For more information on this process, check out this blogpost: https://niallburkley.com/blog/changing-primary-keys-in-ecto/

## Development
### Setup
Requires Erlang, Elixir, a local RabbitMQ instance, a local PostgreSQL database. Clone the repo and run the `bin/setup` script.

### Tests / Linting
This project uses `ExUnit` for tests and Credo for linting code.

### CI Workflow
This project uses [CircleCI](https://app.circleci.com/pipelines/github/learn-co/railway_ipc). All pushes to any branch will trigger a build that runs specs and lints the code.

### Cutting a New Release
Steps for releasing a new version:

* update the version in `mix.exs` and `README.md`
* update the CHANGELOG
  - create a new release heading with the new version number and date
  - create an empty [Unreleased] section with empty headings
  - update links at the bottom to reflect new version
* commit the changes with a message like: "Prepping for release 0.3.0"
* tag the commit with `git tag x.x.x` where `x.x.x` is the new version number
* push the tag to GitHub `git push --tags`
* publish to hex using the command `mix hex.publish`