Polist  

This gem is no longer actively maintained. As a replacement, you can use Resol as well as gems from smart-rb family.

Polist is a set of simple tools for creating business logic layer of your applications:

• Polist::Service is a simple class designed for creating service classes.
• Polist::Builder is a builder system based on Uber::Builder.
• Polist::Struct is a small utility that helps generating simple Struct-like object initializers.

Simply add gem "polist" to your Gemfile.

class MyService < Polist::Service
  def call
    if params[:ok]
      success!(code: :cool)
    else
      fail!(code: :not_cool)
    end
  end
end

service = MyService.run(ok: true)
service.success? #=> true
service.response #=> { code: :cool }

service = MyService.run(ok: false)
service.success? #=> false
service.response #=> { code: :not_cool }

The only parameter that is passed to the service is called params by default. If you want more params, feel free to define your own initializer and call the service accordingly:

class MyService < Polist::Service
  def initialize(a, b, c)
    # ...
  end
end

MyService.call(1, 2, 3)

Unlike .run, .call will raise Polist::Service::Failure exception on failure:

begin
  MyService.call(ok: false)
rescue Polist::Service::Failure => error
  error.response #=> { code: :not_cool }
end

Note that .run and .call are just shortcuts for MyService.new(...).run and MyService.new(...).call with the only difference that they always return the service instance instead of the result of #run or #call. Unlike #call though, #run is not intended to be overwritten in subclasses.

You can use yield in #call. And then call ::run or ::call class methods with block. For example, we have the class:

class BlockFun < Polist::Service
  def call
    success!(yield(1, 2))
  end
end

Then we can use it like this:

service = BlockFun.call { |a, b| a + b }

p service.response # => 3

Behind the scenes it just catches passed block in class methods ::run and ::call, converts it to proc and then passes proc to instance method #call and #run by converting it back to block. So, for example, if you want to pass this block to private methods, you can write code like this:

class AnotherBlockFun < Polist::Service
  def call(&block)
    success!(block_caller(&block))
  end

  private

  def block_caller
    yield 1, 2
  end
end

service = AnotherBlockFun.call { |a, b| a + b }

p service.response # => 3

Sometimes you want to use some kind of params parsing and/or validation, and you can do that with the help of Polist::Service::Form class. It uses tainbox gem under the hood.

class MyService < Polist::Service
  class Form < Polist::Service::Form
    attribute :param1, :String
    attribute :param2, :Integer
    attribute :param3, :String, default: "smth"
    attribute :param4, :String

    validates :param4, presence: true
  end

  def call
    p form.valid?
    p [form.param1, form.param2, form.param3]
  end

  # The commented code is just the default implementation and can be simply overwritten
  # private

  # def form
  #   @form ||= self.class::Form.new(form_attributes.to_snake_keys)
  # end

  # def form_attributes
  #   params
  # end
end

MyService.call(param1: "1", param2: "2") # prints false and then ["1", 2, "smth"]

The #form method is there just for convinience and by default it uses what #form_attributes returns as the attributes for the default form class which is the services' Form class. You are free to use as many different form classes as you want in your service.

The build logic is based on Uber::Builder but it allows recursive builders. See the example:

Can be used with Polist::Service or any other Ruby class.

class User
  include Polist::Builder

  builds do |role|
    case role
    when /admin/
      Admin
    end
  end

  attr_accessor :role

  def initialize(role)
    self.role = role
  end
end

class Admin < User
  builds do |role|
    SuperAdmin if role == "super_admin"
  end

  class SuperAdmin < Admin
    def super?
      true
    end
  end

  def super?
    false
  end
end

User.build("user") # => #<User:... @role="user">

User.build("admin") # => #<Admin:... @role="admin">
User.build("admin").super? # => false

User.build("super_admin") # => #<Admin::SuperAdmin:... @role="super_admin">
User.build("super_admin").super? # => true

Admin.build("smth") # => #<Admin:... @role="admin">
SuperAdmin.build("smth") # => #<Admin::SuperAdmin:... @role="admin">

Works pretty much the same like Ruby Struct class, but you don't have to subclass it.

Can be used with Polist::Service or any other class that don't have initializer specified.

class Point
  include Polist::Struct

  struct :x, :y
end

a = Point.new(15, 25)
a.x # => 15
a.y # => 25

b = Point.new(15, 25, 35) # raises ArgumentError: struct size differs

c = Point.new(15)
c.x # => 15
c.y # => nil

If you have some common things to be done in more than one service, you can define a middleware and register it inside the said services. Every middleware takes the service into it's constructor and executes #call. Thus every middleware has to implement #call method and has a #service attribute reader. Middlewares delegate #success!, #fail!, #error!, #form, #form_attributes to the service class they are registered in. Every middleware should be a subclass of Polist::Service::Middleware. Middlewares are run before the service itself is run.

To register a middleware one should use .register_middleware class method on a service. More than one middleware can be registered for one service.

For example:

class MyMiddleware < Polist::Service::Middleware
  def call
    fail!(code: :not_cool) if service.fail_on_middleware?
  end
end

class MyService < Polist::Service
  register_middleware MyMiddleware

  def call
    success!(code: :cool)
  end

  def fail_on_middleware?
    true
  end
end

service = MyService.run
service.success? #=> false
service.response #=> { code: :not_cool }

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

Released under MIT License.

Created by Yuri Smirnov.