I tried DI with Ruby

What is DI

Dependency injection

Avoiding dependencies by allowing objects to be passed to the constructor from the outside


I will write using Interactor as an example dry-container and dry-auto_inject I tried DI using

Version without DI


module Interactor
  class FindUser
    def initialize(params)
      @params = params

    def call
      user_repo = UserRepository.new

You can see that it depends on UserRepository

dry-container unused version


module Interactor
  class FindUser
    def initialize(params: {}, user_repo: UserRepository.new)
      @params = params
      @user_repo = user_repo

    def call

Initializd arguments tend to be huge and hard to read I have this

dry-container version


module Container
  module FindUser
    extend Dry::Container::Mixin

    #Register the object to be injected
    #You can declare a default object with block
    register "params"

    register "user_repo" do

module Interactor
  class FindUser
    Import = Dry::AutoInject(Container::FindUser)
    #You will be able to call what you include with method
    include Import["params", "user_repo"]

    def call

The code has increased, but the outlook has improved by separating the responsibilities.

Because the Interactor depends on the Container, and the caller (such as Controller) also depends on the Container. I was able to reverse the dependence in a nice way

before: controller -> interactor after: controller -> container <- interactor

What makes me happy

--The code is refreshing

Entrusting initialize to container reduces the responsibility of interactor I want to reduce the responsibilities per class

--Unit tests can be done easily

Interactor test can be done without preparing DB In the above example, you can pass an object that reacts to by_pk (id)


User = Struct.new(:id, :name, :age)

class TestUserRepo
  def by_pk(id)
    User.new(id, "tarou", 20)

params = { id: 1 }
user_repo = TestUserRepo.new
input = { params: params, user_repo: user_repo }


Can be done like

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