NestedGenerators

Ruby on Rails generators for ServiceObject and QueryObject classes and their corresponding unit test files for RSpec framework. Easily extendable.

Introduction

Ruby on Rails enforces unique class names usage inside its app directory.

Following framework's convention to place different class patterns in their own folders, the gem extends autoloaded app directory with other types (like Sidekiq does with its app/workers and rails generate sidekiq:worker generator):

app
├── controllers
│   ├── application_controller.rb
│   └── concerns
├── jobs
│   └── application_job.rb
├── models
│   ├── application_record.rb
│   └── concerns
├── queries
└── services
    └── application_service.rb

ServiceObject Generator

As an old but gold article by CodeClimate states in their second point 2. Extract Service Objects, there are some criteria for when to use ServiceObject pattern - read it, its worth it.

Basic usage

The gem gives you an ability to generate file structure for your ServiceObject classes via CLI, with a single empty public method call.

The simplest:

$ rails generate service potato_peel

$ rails generate service PotatoPeel

results in following:

├── app
│   └── services
│       ├── application_service.rb
│       └── potato_peel_service.rb
├── spec
    └── services
        └── potato_peel_service_spec.rb

so it gives us three files in total:

file 1: app/services/application_service.rb

# frozen_string_literal: true

module Services
  class ApplicationService
    def self.call(*args)
      new(*args).call
    end
  end
end

The first file contains ApplicationService, which simply allows us to call the ServiceObject classes without invoking their .new method - simply pass all your wannabe instance variables to the .call method directly:

PotatoPeelService.call(difficulty: 'medium')

results in the new instance of PotatoPeelService with an instance variable @difficulty = 'medium'.

file 2: app/services/potato_peel_service.rb

# frozen_string_literal: true

module Services
  class PotatoPeelService < ApplicationService
    def initialize
    end

    def call
    end
  end
end

The second file contains PotatoPeelService, which inherits from the ApplicationService and has two empty methods: initialize and call.

As you have probably noticed, ServiceObjects are placed in Services module. I like to keep those that way (hence opinionated), but thankfully Rails is smart enough to find their invocation without Services:: prefix, so you can use both:

Services::PotatoPeelService.call
# and
PotatoPeelService.call

file 3: spec/services/potato_peel_service_spec.rb

# frozen_string_literal: true

RSpec.describe Services::PotatoPeelService do
  describe '#call' do
    pending 'add some examples to (or delete) spec/services/potato_peel_service_spec.rb#call'
  end
end

The third file contains almost empty struture to test our brand new PotatoPeelService, with single describe block for the call method.

Generating methods

The gem allows us to predefine methods for our ServiceObjects.

rails generate service potato_peel public:fast protected:deadline private:sharpen_knife

results in:

file 1: app/services/potato_peel_service.rb

# frozen_string_literal: true

module Services
  class PotatoPeelService < ApplicationService
    def initialize
    end
    
    def call
    end

    def fast
    end

    protected

    def deadline
    end

    private

    def sharpen_knife
    end
  end
end

which is the same file structure as before with additional class methods scoped accordingly.

file 2: spec/services/potato_peel_service_spec.rb

# frozen_string_literal: true

RSpec.describe Services::PotatoPeelService do
  describe '#call' do
    pending 'add some examples to (or delete) spec/services/potato_peel_service_spec.rb#call
  end
  
  describe '#fast' do
    pending 'add some examples to (or delete) spec/services/potato_peel_service_spec.rb#fast
  end
end

and the _spec.rb file contains an additional describe block for the public method passed.

Submodules

It is possible to generate service objects with additional namespaces - generator syntax is the same as with Rails controllers:

$ rails generate service peelers/potato

or even deeper, spearating your modules with backslashes /.

The command call above results in the following:

├── app
│   └── services
│       ├── application_service.rb
│       └── peelers
│           └── potato_service.rb
└── spec
     └── services
          └── peelers
               └── potato_service_spec.rb

file 1: app/services/peelers/potato_service.rb

# frozen_string_literal: true

module Services
  module Peelers
    class PotatoService < ApplicationService
      def initialize
      end

      def call
      end
    end
  end
end

file 2: spec/services/peelers/potato_service_spec.rb

# frozen_string_literal: true

RSpec.describe Services::Peelers::PotatoService do
  describe '#call' do  
    pending 'add some examples to (or delete) spec/services/peelers/potato_service_spec.rb#call
  end
end

And you can pass them public, protected and private methods too, as described in Generating methods section:

$ rails generate service peelers/potato public:fast

results in:

file 1: app/services/peelers/potato_service.rb

# frozen_string_literal: true

module Services
  module Peelers
    class PotatoService < ApplicationService
      def initialize
      end

      def call
      end

      def fast
      end
    end
  end
end

and corresponding:

file 2: spec/services/peelers/potato_service_spec.rb

# frozen_string_literal: true

RSpec.describe Services::Peelers::PotatoService do
  describe '#call' do
    pending 'add some examples to (or delete) spec/services/peelers/potato_service_spec.rb#call'
  end

  describe '#fast' do
    pending 'add some examples to (or delete) spec/services/peelers/potato_service_spec.rb#fast'
  end
end

QueryObject Generator

Quoting the golden article mentioned before:

For complex SQL queries littering the definition of your ActiveRecord subclass (either as scopes or class methods), consider extracting query objects.

Basic usage

The gem gives you an ability to generate classes structure for your QueryObject classes via CLI.

The simplest:

$ rails generate query rotten_potatoes

$ rails generate query rotten_potatoes

results in following:

├── app
│   └── queries
│        └── rotten_potatoes_query.rb
└── spec
     └── queries
          └── rotten_potatoes_query_spec.rb

so it gives us two files in total:

file 1: app/queries/rotten_potatoes_query.rb

# frozen_string_literal: true

module Queries
  class RottenPotatoesQuery < ApplicationService
    def initialize(relation)
      @relation = relation
    end
  end
end

The first file contains RottenPotatoesQuery which has single initialize method, with a single relation argument assigned to the @relation instance variable.

As you have probably noticed, QueryObjects are placed in Queries module, just like ServiceObjects are placed in the Services module. I like to keep those that way (hence opinionated), but thankfully Rails is smart enough to find their invocation without Queries:: prefix, so you can use both:

Queries::RottenPotatoesQuery.new
# and
RottenPotatoesQuery.new

file 2: spec/services/potato_peel_service_spec.rb

# frozen_string_literal: true

RSpec.describe Queries::RottenPotatoesQuery do
  pending 'add some examples to (or delete) spec/queries/rotten_potatoes_query_spec.rb'
end

The second file contains an empty struture to test our brand new RottenPotatoesQuery.

Generating methods

The gem allows us to predefine methods for our QueryObjects, same as for ServiceObjects.

rails generate query rotten_potatoes public:find protected:empty_bag private:out_of_date

results in:

file 1: app/queries/rotten_potatoes_query.rb

# frozen_string_literal: true

module Queries
  class RottenPotatoesQuery
    def initialize(relation)
      @relation = relation
    end

    def find
    end

    protected

    def empty_bag
    end

    private

    def out_of_date
    end
  end
end

which is the same file structure as before with additional class methods scoped accordingly.

file 2: spec/services/potato_peel_service_spec.rb

# frozen_string_literal: true

RSpec.describe Queries::RottenPotatoesQuery do
  describe '#find' do
    pending 'add some examples to (or delete) spec/queries/rotten_potatoes_query_spec.rb#find'
  end
end

and the _spec.rb file a describe block for the public method passed.

Submodules

It is possible to generate query objects with additional namespaces - generator syntax is the same as with Rails controllers or ServiceObjects:

$ rails generate query rotten_vegetables/potatoes

or even deeper, spearating your modules with backslashes /.

The command call above results in the following:

├── app
│   └── queries
│       └── rotten_vegetables
│           └── potatoes_query.rb
└── spec
     └── queries
          └── rotten_vegetables
              └── potatoes_query_spec.rb

file 1: app/queries/rotten_vegetables/potatoes_query.rb

# frozen_string_literal: true

module Queries
  module RottenVegetables
    class PotatoesQuery
      def initialize(relation)
        @relation = relation
      end
    end
  end
end

file 2: spec/queries/rotten_vegetables/potatoes_query_spec.rb

# frozen_string_literal: true

RSpec.describe Queries::RottenVegetables::PotatoesQuery do
  pending 'add some examples to (or delete) spec/queries/rotten_vegetables/potatoes_query_spec.rb'
end

And you can pass them public, protected and private methods too, as described in Generating methods section:

$ rails generate query rotten_vegetables/potatoes public:find

results in:

file 1: app/services/peelers/potato_service.rb

# frozen_string_literal: true

module Queries
  module RottenVegetables
    class PotatoesQuery
      def initialize(relation)
        @relation = relation
      end

      def find
      end
    end
  end
end

and corresponding:

file 2: spec/services/peelers/potato_service_spec.rb

# frozen_string_literal: true

RSpec.describe Queries::RottenVegetables::PotatoesQuery do
  describe '#find' do
    pending 'add some examples to (or delete) spec/queries/rotten_vegetables/potatoes_query_spec.rb#find'
  end
end

Advanced usage - creating your own generators

As you've probably noticed, ServiceObject generator and QueryObject generator are very similar. They both inherit from the NestedGeneratorsBaseGenerator class, which includes bunch of helpful methods to write your own generator, with support for nesting and passing method names via CLI.

Step by step guide

In this short guide, we will create our own ValueObject generator:

Step 1

In your lib directory, create generators/value/templates subdirectories:

mkdir -p lib/generators/value/templates

Step 2

Create our value_generator.rb, next to templates directory:

touch lib/generators/value/value_generator.rb

Step 3

In the lib/generators/value/templates directory, create two templates, one for the ValueObject class and second for its tests

touch lib/generators/templates/class_template.erb
touch lib/generators/templates/class_spec_template.erb

Step 4

Start with editing value_generator.rb file; open it in your text editor and paste the following code:

# frozen_string_literal: true

require 'generators/nested_generators_base_generator'

class ValueGenerator < NestedGeneratorsBaseGenerator
  source_root File.expand_path('templates', __dir__)

  def initialize(*args, &block)
    super
    @type = 'value'
  end

  def create_value_file
    create_class_file
    create_class_spec_file
  end
end

Step 5

Next, open the templates/class_template.erb and paste the following code:

# frozen_string_literal: true

<%= open_modules_nesting %><%= open_class %>
<%= code_indent %>include Comparable

<%= code_indent %>def initialize
<%= code_indent %>end

<%- SCOPES.each.with_index do |name, index| -%>
  <%- if index.zero? -%>
    <%- if scope?(name) -%>
      <%- scope_methods(name).each do |method| %>
<%= code_indent %>def <%= method.gsub("#{name}:", '') %>
<%= code_indent %>end
      <%- end -%>
    <%- end -%>
  <%- else -%>
    <%- if scope?(name) -%><%- %>
<%- %><%= code_indent %><%= name %>
      <%- scope_methods(name).each do |method| %>
<%= code_indent %>def <%= method.gsub("#{name}:", '') %>
<%= code_indent %>end
      <%- end -%>
    <%- end -%>
  <%- end -%>
<%- end -%>
<%= end_class %><%= close_modules_nesting %>

Step 6

And at last, edit the templates/class_spec_template.erb with:

# frozen_string_literal: true

RSpec.describe <%= @type.capitalize.pluralize %>::<%= class_name %><%= @type.capitalize %> do
  <%- if scope?('public') -%>
    <%- scope_methods('public').each do |method| -%>
  describe '#<%= strip_scope(method, 'public') %>' do
    <%= rspec_empty_message(strip_scope(method, 'public')) %>
  end
    
    <%- end -%>
  <%- else -%>
  <%= rspec_empty_message %>
  <%- end -%>
end

Step 7 - Use it!

Your done, congrats. Now, you can use:

rails generate value rating 'public:better_than?' 'public:<=>' public:hash 'public:eql?' public:to_s

resulting in

file 1: app/values/rating_value.rb

# frozen_string_literal: true

module Values
  class RatingValue
    include Comparable

    def initialize
    end

    def better_than?
    end

    def <=>
    end

    def hash
    end

    def eql?
    end

    def to_s
    end
  end
end

and

file 2: spec/values/rating_value_spec.rb

# frozen_string_literal: true

RSpec.describe Values::RatingValue do
  describe '#better_than?' do
    pending 'add some examples to (or delete) spec/values/rating_value_spec.rb#better_than?'
  end

  describe '#<=>' do
    pending 'add some examples to (or delete) spec/values/rating_value_spec.rb#<=>'
  end

  describe '#hash' do
    pending 'add some examples to (or delete) spec/values/rating_value_spec.rb#hash'
  end

  describe '#eql?' do
    pending 'add some examples to (or delete) spec/values/rating_value_spec.rb#eql?'
  end

  describe '#to_s' do
    pending 'add some examples to (or delete) spec/values/rating_value_spec.rb#to_s'
  end
end

And the nested version, like ServiceObject and QueryObject do.

License

The MIT License