Lite::Command

Lite::Command provides an API for building simple and complex command based service objects. It provides extensions for handling errors and memoization to improve your object workflow productivity.

Installation

Add this line to your application's Gemfile:

gem 'lite-command'

And then execute:

$ bundle

Or install it yourself as:

$ gem install lite-command

Table of Contents

• Setup
• Simple
• Complex
• Procedure
• Extensions

Setup

rails g command NAME will generate the following file:

app/commands/[NAME]_command.rb

If a ApplicationCommand file in the app/commands directory is available, the generator will create file that inherit from ApplicationCommand if not it will fallback to Lite::Command::Complex.

Simple

Simple commands are a traditional command service call objects. It only exposes a call method that returns a value.

Setup

class CalculatePower < Lite::Command::Simple

  # NOTE: This `execute` class method is required to use with call
  def self.execute(a, b)
    a**b
  end

end

Callers

CalculatePower.execute(2, 2) #=> 4

# - or -

CalculatePower.call(2, 3) #=> 8

Complex

Complex commands are powerful command service call objects. It can be extended to use error, memoization, and propagation mixins.

Setup

class SearchMovies < Lite::Command::Complex

  attr_reader :name

  def initialize(name)
    @name = name
  end

  # NOTE: This `execute` instance method is required to use with call
  def execute
    { generate_fingerprint => movies_by_name }
  end

  private

  def movies_by_name
    HTTP.get("http://movies.com?title=#{name}")
  end

  def generate_fingerprint
    Digest::MD5.hexdigest(movies_by_name)
  end

end

Caller

SearchMovies.execute('Toy Story') #=> { 'fingerprint_1' => [ 'Toy Story 1', ... ] }

# - or -

command = SearchMovies.new('Toy Story')
command.called? #=> false
command.call    #=> { 'fingerprint_1' => [ 'Toy Story 1', ... ] }
command.called? #=> true

# - or -

command = SearchMovies.call('Toy Story')
command.called? #=> true
command.call    #=> { 'fingerprint_1' => [ 'Toy Story 1', ... ] }

Result

command = SearchMovies.new('Toy Story')
command.result  #=> nil

command.call    #=> { 'fingerprint_1' => [ 'Toy Story 1', ... ] }
command.result  #=> { 'fingerprint_1' => [ 'Toy Story 1', ... ] }

command.recall! #=> Clears the `call`, `cache`, `errors` variables and then re-performs the call
command.result  #=> { 'fingerprint_2' => [ 'Toy Story 2', ... ] }

Procedure

Procedures are used to run a collection of commands. It uses the the complex procedure API so it has access to all the methods. The execute method is already defined to handle most common procedure steps. It can be use directly or subclassed.

Setup

class SearchChannels < Lite::Command::Procedure; end

commands = [DisneyChannel.new, EspnChannel.new(current_station), MtvChannel.new]

procedure = SearchChannels.call(*commands)
procedure.result #=> ['disney: #3', 'espn: #59', 'mtv: #212']
procedure.steps  #=> [<DisneyChannel  @result="...">, <EspnChannel @result="...">, <MtvChannel  @result="...">]

# - or -

# If the errors extension is added you can stop the procedure at first failure.
procedure = SearchChannels.new(*commands)
procedure.exit_on_failure = true
procedure.call
procedure.result #=> ['disney: #3']
procedure.failed_steps #=> [{ index: 1, step: 2, name: 'ErrorChannel', args: [current_station], errors: ['field error message'] }]

Extensions

Extend complex (and procedures) base command with any of the following extensions:

Errors (optional)

Learn more about using Lite::Errors

Setup

class SearchMovies < Lite::Command::Complex
  include Lite::Command::Extensions::Errors

  # ... ommited ...

  private

  # Add a explicit and/or exception errors to the error pool
  def generate_fingerprint
    if movies_by_name.nil?
      errors.add(:fingerprint, 'invalid md5 request value')
    else
      Digest::MD5.hexdigest(movies_by_name)
    end
  rescue ArgumentError => exception
    merge_exception!(exception, key: :custom_error_key)
  end

end

Instance Callers

command = SearchMovies.call('Toy Story')
command.errors    #=> Lite::Errors::Messages object

command.validate! #=> Raises Lite::Command::ValidationError if it has any errors
command.valid?    #=> Alias for validate!

command.errored?  #=> false
command.success?  #=> true
command.failure?  #=> Checks that it has been called and has errors
command.status    #=> :failure

command.result!   #=> Raises Lite::Command::ValidationError if it has any errors, if not it returns the result

# Use the following to merge errors from other commands or models
# with the default direction being `:from`
command.merge_errors!(command_2)
user_model.merge_errors!(command, direction: :to)

Block Callers

# Useful for controllers or actions that depend on states.
SearchMovies.perform('Toy Story') do |result, success, failure|
  success.call { redirect_to(movie_path, notice: "Movie can be found at: #{result}") }
  failure.call { redirect_to(root_path, notice: "Movie cannot be found at: #{result}") }
end

Propagation (optional)

Propagation methods help you perform an action on an object. If successful is returns the result else it adds the object errors to the form object. Available propagation methods are:

• assign_and_return!(object, params)
• create_and_return!(klass, params)
• update_and_return!(object, params)
• destroy_and_return!(object)
• archive_and_return!(object) (if using Lite::Archive)
• save_and_return!(object)

Setup

class SearchMovies < Lite::Command::Complex
  include Lite::Command::Extensions::Errors
  include Lite::Command::Extensions::Propagation

  # ... ommited ...

  def execute
    create_and_return!(User, name: 'John Doe')
  end

end

Memoize (optional)

Learn more about using Lite::Memoize

Setup

class SearchMovies < Lite::Command::Complex
  include Lite::Command::Extensions::Memoize

  # ... ommited ...

  private

  # Sets the value in the cache
  # Subsequent method calls gets the cached value
  # This saves you the extra external HTTP.get call
  def movies_by_name
    cache.memoize { HTTP.get("http://movies.com?title=#{name}") }
  end

  # Gets the value in the cache
  def generate_fingerprint
    Digest::MD5.hexdigest(movies_by_name)
  end

end

Callers

command = SearchMovies.call('Toy Story')
command.cache #=> Lite::Memoize::Instance object

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 will allow 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/[USERNAME]/lite-command. This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the Contributor Covenant code of conduct.

License

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

Code of Conduct

Everyone interacting in the Lite::Command project’s codebases, issue trackers, chat rooms and mailing lists is expected to follow the code of conduct.