ex_operation

# ExOperation
A library for making domain operations wrapped in a single database transaction.
**WARNING:** This library is in active development state. Breaking changes are possible between minor releases.
## Example
An operation definition:
```elixir
defmodule MyApp.Book.Update do
  use ExOperation, params: %{
    id!: :integer,
    title!: :string,
    author_id: :integer
  }
  def validate_params(changeset) do
    changeset
    |> Ecto.Changeset.validate_length(:title, min: 5)
  end
  def call(operation) do
    operation
    |> find(:book, schema: MyApp.Book, preload: [:author])
    |> find(:author, schema: MyApp.Author, id_path: [:author_id], optional: true)
    |> step(:result, &do_update(operation.context, &1, operation.params))
    |> after_commit(&send_notifcation(&1))
  end
  defp do_update(context, txn, params) do
    txn.book
    |> Ecto.Changeset.cast(params, [:title])
    |> Ecto.Changeset.put_assoc(:author, txn.author)
    |> Ecto.Changeset.put_assoc(:updated_by, context.current_user)
    |> MyApp.Repo.update()
  end
  defp send_notification(txn) do
    # …
    {:ok, txn}
  end
end
```
The call:
```elixir
context = %{current_user: current_user}
with {:ok, %{result: book}} <- MyApp.Book.Update |> ExOperation.run(context, params) do
  # …
end
```
### Usage with Phoenix
An example Phoenix app can be found here: [ex_operation_phoenix_example](https://github.com/feymartynov/ex_operation_phoenix_example).
## Features
* [Railway oriented](https://fsharpforfunandprofit.com/rop/) domain logic pipeline.
* Running all steps in a single database transaction. It uses [Ecto.Multi](https://hexdocs.pm/ecto/Ecto.Multi.html) inside.
* Params casting & validation with `Ecto.Changeset`. Thanks to [params](https://github.com/vic/params) library.
* Convenient fetching of entitites from the database.
* Context passing. Useful for passing current user, current locale etc.
* Composable operations: one operation can call another through `suboperation/3` function.
* Changing operation scenario based on previous steps results with `defer/2`.
* After commit hooks for scheduling asynchronous things.
## Installation
Add the following to your `mix.exs` and then run `mix deps.get`:
```elixir
def deps do
  [
    {:ex_operation, "~> 0.4.0"}
  ]
end
```
Add to your `config/config.exs`:
```elixir
config :ex_operation,
  repo: MyApp.Repo
```
where `MyApp.Repo` is the name of your Ecto.Repo module.