Richer Service Objects with Hanami Interactors

Transcript

1. Richer Services with Hanami Interactors
   

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2. Services
   Objects used to orchestrate the business logic
   between your controllers (or any other business
   logic) and the persistence layer
   » Service Objects (Rails)
   » Use Case Objects/Interactor (Hanami)
   » Operations (Trailblazer)
   

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3. Hanami Interactors
   Hanami implementation of Service Objects
   » Part of hanami-utils gem
   » Small API
   » Configurable Result
   » Internal State Exposure
   

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4. Successful Example
   require 'hanami/interactor'
   class Signup
   include Hanami::Interactor
   expose :user, :params
   def initialize(params)
   @params = params
   @user = User.new(@params)
   @foo = 'bar'
   end
   def call
   @user = UserRepository.persist(@user)
   end
   end
   

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5. Successful Example
   result = Signup.new(name: 'Krombopulos Michael').call
   result.failure? # => false
   result.successful? # => true
   result.user # => #
   result.params # => { :name=>"Krombopulos Michael" }
   result.foo # => raises NoMethodError
   

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6. Failing Example
   require 'hanami/interactor'
   class Signup
   include Hanami::Interactor
   expose :user
   def initialize(params)
   @params = params
   @user = User.new(@params)
   end
   # THIS WON'T BE INVOKED BECAUSE #valid? WILL RETURN false
   def call
   @user = UserRepository.persist(@user)
   end
   private
   # super always return true
   # It's desined to be overriden in each child class
   def valid?
   false
   end
   end
   

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7. Failing Example
   result = Signup.new(name: "Krombopulous Michael").call
   result.successful? # => false
   result.failure? # => true
   result.user # => #
   

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8. Caveats
   As per current hanami-utils version (1.0.0),
   parameters cannot be passed to the #call method, only
   to #new.1
   » cause of very limited Dependecy Injection
   » Interactor instance cannot be reused with other
   parameters
   1 This will be changed in hanami-utils 1.1.0. See this PR for more details.
   

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9. Refactoring an Action with Interactor
   class TasksController < ApplicationController
   def assign_checklist
   checklist_details = params[:task][:checklist]
   checklist = current_user.organisation.checklists.find(checklist_details[:id])
   tasks = Task.transaction do
   checklist.items.map do |description|
   task = scope.new(resource_params.merge(description: description))
   authorize! :create, task
   unless task.save
   render_errors(task)
   raise ActiveRecord::Rollback.new
   end
   task
   end
   end
   if tasks.present?
   render json: TaskMapper.all_as_json(tasks, scope: current_user)
   end
   end
   end
   

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10. What we need to know about the application?
    » The application has a Cheklist and a Task model
    » A collection of Task can be created from a
    Checklist
    

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11. What does the action do?
    » Creates one Task per Checklist item
    » Authorize creation of each task
    » Task resources are all the same (passed on
    resource_params), except for description that is
    set to the Checklist item
    » Handles database transaction rollback if any Task
    fails to be saved
    » Handles rendering of errors or tasks depending if
    any error happened or not
    

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12. This
    action
    is doing
    too much
    

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13. What should this action be doing?
    » Check user authorization for whole action
    » Pass params, and any other argument necessary, to
    a service that handle the actual creation work
    » Handle rendering of errors or tasks based on
    service result
    

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14. Where should
    the creation
    code live?
    

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15. Enter
    Hanami
    Interactors
    

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16. Implementing the Interactor Class
    require 'hanami/interactor'
    class ChecklistTasksFactory
    include Hanami::Interactor
    def initialize(checklist_params, task_params, current_user)
    @checklist = current_user.organisation.checklists.find(checklist_params[:id])
    @task_params = task_params
    @scope = current_user.organisation.tasks
    @tasks = []
    end
    # ...
    end
    

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17. Refactoring the Controller Action
    class TasksController < ApplicationController
    def assign_checklist
    authorize! :create_from_checklist, Task
    # resource_params comes from our private API
    interactor = ChecklistTasksFactory.new(checklist_params, resource_params, current_user)
    # ...
    end
    private
    def checklist_params
    params.require(:task).permit(checklist: [:id])
    end
    end
    

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18. Implementing the Interactor Class
    require 'hanami/interactor'
    class ChecklistTasksFactory
    include Hanami::Interactor
    def initialize(checklist_params, task_params, current_user)
    @checklist = current_user.organisation.checklists.find(checklist_params[:id])
    @task_params = task_params
    @scope = current_user.organisation.tasks
    @tasks = []
    end
    def call
    @tasks = Task.transaction do
    @checklist.items.map do |description|
    build_task(description)
    save_task!
    @task
    end
    end
    end
    private
    def build_task(description)
    @task = @scope.new(@task_params.merge(description: description))
    end
    def save_task!
    return if @task.save
    add_error(@task)
    raise ActiveRecord::Rollback
    end
    end
    

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19. Refactoring the Controller Action
    class TasksController < ApplicationController
    def assign_checklist
    authorize! :create_from_checklist, Task
    # resource_params comes from our private API
    interactor = ChecklistTasksFactory.new(checklist_params, resource_params, current_user)
    result = interactor.call
    if result.successful?
    # result.tasks will raise NoMethodError as tasks is not exposed by the interactor
    render json: TaskMapper.all_as_json(result.tasks, scope: current_user)
    else
    # Interactor::Result exposes #errors by default
    render_errors(result.errors)
    end
    end
    private
    def checklist_params
    params.require(:task).permit(checklist: [:id])
    end
    end
    

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20. The complete Interactor
    require 'hanami/interactor'
    class ChecklistTasksFactory
    include Hanami::Interactor
    expose :tasks
    def initialize(checklist_params, task_params, current_user)
    @checklist = current_user.organisation.checklists.find(checklist_params[:id])
    @task_params = task_params
    @scope = current_user.organisation.tasks
    @tasks = []
    end
    def call
    @tasks = Task.transaction do
    @checklist.items.map do |description|
    build_task(description)
    save_task!
    @task
    end
    end
    end
    private
    def build_task(description)
    @task = @scope.new(@task_params.merge(description: description))
    end
    def save_task!
    return if @task.save
    add_error(@task)
    raise ActiveRecord::Rollback
    end
    end
    

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21. And that's
    How Interactors
    Can help you
    Organise your code
    

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22. Questions?
    

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