# Lite::Command
[](http://badge.fury.io/rb/lite-command)
[](https://travis-ci.org/drexed/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:
```ruby
gem 'lite-command'
```
And then execute:
$ bundle
Or install it yourself as:
$ gem install lite-command
## Table of Contents
* [Setup](#setup)
* [Simple](#simple)
* [Complex](#complex)
* [Procedure](#procedure)
* [Extensions](#extensions)
## Setup
`rails g command NAME` will generate the following file:
```erb
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**
```ruby
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**
```ruby
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**
```ruby
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**
```ruby
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**
```ruby
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**
```ruby
class SearchChannels < Lite::Command::Procedure; end
```
```ruby
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](https://github.com/drexed/lite-errors)
**Setup**
```ruby
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**
```ruby
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**
```ruby
# 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**
```ruby
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](https://github.com/drexed/lite-memoize)
**Setup**
```ruby
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**
```ruby
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](https://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](http://contributor-covenant.org) code of conduct.
## License
The gem is available as open source under the terms of the [MIT License](https://opensource.org/licenses/MIT).
## 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](https://github.com/[USERNAME]/lite-command/blob/master/CODE_OF_CONDUCT.md).