Rails Conventions

Rails Conventions

Opinionated Rails patterns for clean, maintainable code.

Core Philosophy

1. Duplication > Complexity: Simple duplicated code beats complex DRY abstractions

   • "I'd rather have four simple controllers than three complex ones"

2. Testability = Quality: If it's hard to test, structure needs refactoring

3. Adding controllers is never bad. Making controllers complex IS bad.

Turbo Streams

Simple turbo streams MUST be inline in controllers:

# FAIL: Separate .turbo_stream.erb files for simple operations
render "posts/update"

# PASS: Inline array
render turbo_stream: [
  turbo_stream.replace("post_#{@post.id}", partial: "posts/post", locals: { post: @post }),
  turbo_stream.remove("flash")
]

Controller & Concerns

Business logic belongs in models or concerns, not controllers.

# Concern structure
module Dispatchable
  extend ActiveSupport::Concern

  included do
    scope :available, -> { where(status: "pending") }
  end

  class_methods do
    def claim!(batch_size)
      # class-level behavior
    end
  end
end

Service Extraction

Extract when you see MULTIPLE of:

• Complex business rules (not just "it's long")
• Multiple models orchestrated
• External API interactions
• Reusable cross-controller logic

Service structure:

• Single public method
• Namespace by responsibility (Extraction::RegexExtractor)
• Constructor takes dependencies
• Return data structures, not domain objects

Modern Ruby Style

# Hash shorthand
{ id:, slug:, doc_type: kind }

# Safe navigation
created_at&.iso8601
@setting ||= SlugSetting.active.find_by!(slug:)

# Keyword arguments
def extract(document_type:, subject:, filename:)
def process!(strategy: nil)

Enum Patterns

# Frozen arrays with validation
STATUSES = %w[processed needs_review].freeze
enum :status, STATUSES.index_by(&:itself), validate: true

Scope Patterns

# Guard with .present?, chainable design
scope :by_slug, ->(slug) { where(slug:) if slug.present? }
scope :from_date, ->(date) { where(created_at: Date.parse(date).beginning_of_day..) if date.present? }

def self.filtered(params)
  all.by_slug(params[:slug]).by_kind(params[:kind])
rescue ArgumentError
  all
end

Error Handling

# Domain-specific errors
class InactiveSlug < StandardError; end

# Log with context, re-raise for upstream
def handle_exception!(error:)
  log_error("Exception #{error.class}: #{error.message}", error:)
  mark_failed!(error.message)
  raise
end

Testing (Minitest + Fixtures)

test "describes expected behavior" do
  email = emails(:two)
  email.process
  email.reload
  assert_equal "finished", email.processing_status
end

Principles:

• Behavior-driven: Test what, not how
• Fixture-based: Use emails(:two) for setup
• Mock externals: Stub S3, APIs, PDFs
• State verification: .reload after operations
• Helper methods: build_valid_email, with_stubbed_download

Naming (5-Second Rule)

If you can't understand in 5 seconds:

# FAIL
show_in_frame
process_stuff

# PASS
fact_check_modal
_fact_frame

JavaScript & Importmap

Rails 7+ uses importmap for JS dependency management. Scope dependencies to the narrowest entrypoint.

Multiple Entrypoints

# config/importmap.rb
pin "application"                    # Public entrypoint
pin "@hotwired/turbo-rails", to: "turbo.min.js"
pin "@hotwired/stimulus", to: "stimulus.min.js"

# Admin-only dependencies - pinned but only imported in admin entrypoint
pin "chartkick", to: "chartkick.js"
pin "Chart.bundle", to: "Chart.bundle.js"

// app/javascript/application.js — public pages only
import "@hotwired/turbo-rails"
import "@hotwired/stimulus"
import "controllers"

// app/javascript/admin.js — imports public base + admin-only libs
import "application"
import "chartkick"
import "Chart.bundle"

<%# Admin layout %>
<%= javascript_importmap_tags("admin") %>

<%# All other layouts %>
<%= javascript_importmap_tags %>

Adding New JS Dependencies

1. Determine scope: public-facing or admin-only?
2. Pin in config/importmap.rb
3. Import in the correct entrypoint
4. Never add admin-only libraries to application.js

Performance

• Consider scale impact
• No premature caching
• KISS - Keep It Simple
• Indexes slow writes - add only when needed