register-provider

Use this skill when registering external dependencies (database, mailer, cache, third-party APIs) in the Hanami 2.x DI container.

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Core Rules

1. Generate a provider using the Hanami CLI:

   hanami generate provider mailer

   This creates config/providers/mailer.rb.

2. Implement the provider using lifecycle hooks: Use prepare for requiring dependencies and start for component initialization. Keep providers focused on a single external dependency or library.

   # config/providers/mailer.rb
   # frozen_string_literal: true
   
   Hanami.app.register_provider(:mailer) do
     prepare do
       require "mail"
     end
   
     start do
       client = Mail.new do
         delivery_method :smtp, {
           address: target[:settings].smtp_host,
           port: target[:settings].smtp_port
         }
       end
   
       register("mailer.client", client)
     end
   end

   Validation checkpoint: After implementing the provider, verify it loads correctly before writing consuming code:

   # In `hanami console`
   Hanami.app["mailer.client"]   # => should return the registered instance without errors

   If this raises or returns nil, fix the provider before proceeding.

3. Access provided components via Deps:

   # app/mailers/welcome.rb
   module MyApp
     module Mailers
       class Welcome
         include Deps["mailer.client"]
   
         def deliver(user)
           client.deliver do
             to user.email
             subject "Welcome!"
           end
         end
       end
     end
   end

4. Use the built-in database provider: The ROM container is automatically registered at boot by the framework:

   include Deps["db.rom"]

5. Register third-party API clients using settings: Always load keys and URLs through target[:settings]. Do not reference raw environment variables via ENV in providers.

6. Rescue and log errors in start to control boot failure behavior. Choose one of two strategies:

   • Swallow the error (register a null/fallback object) if the service is optional and the app should still boot without it.
   • Re-raise the error if the service is required and a missing provider should halt boot.

   # config/providers/storage.rb
   Hanami.app.register_provider(:storage) do
     prepare do
       require "aws-sdk-s3"
     end
   
     start do
       client = Aws::S3::Client.new(
         access_key_id: [REDACTED:API key param],
         secret_access_key: target[:settings].cloud_storage_secret,
         region: target[:settings].cloud_storage_region
       )
       register("storage.client", client)
     rescue StandardError => e
       target[:logger].error("[provider:storage] failed to start: #{e.message}")
       # Re-raise if this provider is required for the app to function:
       raise
       # Or register a null object and swallow if the service is optional:
       # register("storage.client", NullStorageClient.new)
     end
   end

7. Test components that depend on providers by stubbing the provided dependency:

   stub_mailer = double("mailer", deliver: true)
   welcome = MyApp::Mailers::Welcome.new(mailer__client: stub_mailer)

8. Verify a provider is correctly registered using the Hanami console or a smoke test:

   # In `hanami console`
   Hanami.app["mailer.client"]   # => returns the registered instance

   For a lightweight smoke test in specs:

   it "registers the mailer client" do
     expect(Hanami.app["mailer.client"]).to be_a(Mail::Message)
   end

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Integration