FService

Simpler, safer and more composable operations

FService is a small gem that provides a base class for your services (aka operations). The goal is to make services simpler, safer, and more composable. It uses the Result monad for handling operations.

Installation

Add this line to your application's Gemfile:

gem 'f_service'

And then execute:

$ bundle

Or install it yourself as:

$ gem install f_service

Usage

Creating your service

To start using it, you have to create your service class inheriting from FService::Base.

class User::Create < FService::Base
end

Now, define your initializer to setup data.

class User::Create < FService::Base
  def initialize(name:)
    @name = name
  end
end

The next step is writing the #run method, which is where the work should be done. Use the methods #Success and #Failure to handle your return values. You can optionally specify a list of types which represents that result and a value for your result.

class User::Create < FService::Base
  # ...
  def run
    return Failure(:no_name, :invalid_attribute) if @name.nil?

    user = UserRepository.create(name: @name)
    if user.save
      Success(:success, :created, data: user)
    else
      Failure(:creation_failed, data: user.errors)
    end
  end
end

Remember, you have to return an FService::Result at the end of your services.

Using your service

To run your service, use the method #call provided by FService::Base. We like to use the implicit call, but you can use it in the form you like most.

User::Create.(name: name)
# or
User::Create.call(name: name)

We do not recommend manually initializing and running your service because it will not type check your result (and you could lose nice features like pattern matching and service chaining)!

Using the result

Use the methods #successful? and #failed? to check the status of your result. If it is successful, you can access the value with #value, and if your service fails, you can access the error with #error.

A hypothetical controller action using the example service could look like this:

class UsersController < BaseController
  def create
    result = User::Create.(user_params)

    if result.successful?
      json_success(result.value)
    else
      json_error(result.error)
    end
  end
end

Note that you're not limited to using services inside controllers. They're just PORO's (Play Old Ruby Objects), so you can use in controllers, models, etc. (even other services!).

Pattern matching

The code above could be rewritten using the #on_success and #on_failure hooks. They work similar to pattern matching:

class UsersController < BaseController
  def create
    User::Create.(user_params)
                .on_success { |value| return json_success(value) }
                .on_failure { |error| return json_error(error) }
  end
end

Or else it is possible to specify an unhandled option to ensure that the callback will process that message anyway the error.

class UsersController < BaseController
  def create
    User::Create.(user_params)
                .on_success(unhandled: true) { |value| return json_success(value) }
                .on_failure(unhandled: true) { |error| return json_error(error) }
  end
end

class UsersController < BaseController
  def create
    User::Create.(user_params)
                .on_success { |value| return json_success(value) }
                .on_failure { |error| return json_error(error) }
  end
end

You can ignore any of the callbacks, if you want to.

Going further, you can match the Result type, in case you want to handle them differently:

class UsersController < BaseController
  def create
    User::Create.(user_params)
                .on_success(:user_created) { |value| return json_success(value) }
                .on_success(:user_already_exists) { |value| return json_success(value) }
                .on_failure(:invalid_data) { |error| return json_error(error) }
                .on_failure(:critical_error) do |error|
                  MyLogger.report_failure(error)

                  return json_error(error)
                end
  end
end

It's possible to provide multiple types to the hooks too. If the result type matches any of the given types, the hook will run.

class UsersController < BaseController
  def create
    User::Create.(user_params)
                .on_success(:user_created, :user_already_exists) { |value| return json_success(value) }
                .on_failure(:invalid_data) { |error| return json_error(error) }
                .on_failure(:critical_error) do |error|
                  MyLogger.report_failure(error)

                  return json_error(error)
                end
  end
end

Type precedence

FService matches the service's types from left to right, from more specific to more generic. For example, the following result Failure(:unprocessable_entity, :client_error, :http_response) will match in the following order:

:unprocessable_entity;
:client_error;
:http_response;
unmatched block;

Chaining services

Since all services return Results, you can chain service calls making a data pipeline. If some step fails, it will short circuit the call chain.

class UsersController < BaseController
  def create
    result = User::Create.(user_params)
                         .and_then { |user| User::Login.(user) }
                         .and_then { |user| User::SendWelcomeEmail.(user) }

    if result.successful?
      json_success(result.value)
    else
      json_error(result.error)
    end
  end
end

You can use the .to_proc method on FService::Base to avoid explicit inputs when chaining services:

class UsersController < BaseController
  def create
    result = User::Create.(user_params)
                         .and_then(&User::Login)
                         .and_then(&User::SendWelcomeEmail)
    # ...
  end
end

`Check` and `Try`

You can use Check to converts a boolean to a Result, truthy values map to Success, and falsey values map to Failures:

Check(:math_works) { 1 < 2 }
# => #<Success @value=true, @types=[:math_works]>

Check(:math_works) { 1 > 2 }
# => #<Failure @error=false, @types=[:math_works]>

Try transforms an exception into a Failure if some exception is raised for the given block. You can specify which exception class to watch for using the parameter catch.

class IHateEvenNumbers < FService::Base
  def run
    Try(:rand_int) do
      n = rand(1..10)
      raise "Yuck! It's a #{n}" if n.even?

      n
    end
  end
end

IHateEvenNumbers.call
# => #<Success @value=9, @types=[:rand_int]>

IHateEvenNumbers.call
# => #<Failure @error=#<RuntimeError: Yuck! It's a 4>, @types=[:rand_int]>

Testing

We provide some helpers and matchers to make ease to test code envolving Fservice services.

To make available in the system, in the file 'spec/spec_helper.rb' or 'spec/rails_helper.rb'

add the folowing require:

require 'f_service/rspec'

Mocking a result

mock_service(Uer::Create)
# => Mocks a successful result with all values nil

mock_service(Uer::Create, result: :success)
# => Mocks a successful result with all values nil

mock_service(Uer::Create, result: :success, types: [:created, :success])
# => Mocks a successful result with type created

mock_service(Uer::Create, result: :success, types: :created, value: instance_spy(User))
# => Mocks a successful result with type created and a value

mock_service(Uer::Create, result: :failure)
# => Mocs a failure with all nil values

mock_service(User::Create, result: :failure, types: [:unprocessable_entity, :client_error])
# => Mocs a failure with a failure type

mock_service(User::Create, result: :failure, types: [:unprocessable_entity, :client_error], value: { name: ["can't be blank"] })
# => Mocs a failure with a failure type and an error value

Matching a result

expect(User::Create.(name: 'Joe')).to have_succeed_with(:created)

expect(User::Create.(name: 'Joe')).to have_succeed_with(:created).and_value(an_instance_of(User))

expect(User::Create.(name: nil)).to have_failed_with(:invalid_attributes)

expect(User::Create.(name: nil)).to have_failed_with(:invalid_attributes).and_error({ name: ["can't be blank"] })

expect(User::Create.(name: nil)).to have_failed_with(:invalid_attributes).and_error(a_hash_including(name: ["can't be blank"]))

API Docs

You can access the API docs here.

Development

After checking out the repo, run bin/setup to install dependencies. Then, run rake spec to run the tests. You can also run bin/console for an interactive prompt that allows you to experiment.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and tags, and push the .gem file to rubygems.org.

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/Fretadao/f_service.

License

The gem is available as open-source under the terms of the MIT License.

f_service