Purpose

AI assistants can accelerate Rails development when used effectively.

This document provides prompt patterns and workflows for using AI assistants in common Rails development tasks: model generation, API development, testing, debugging and refactoring.

Workflows

Model and Migration Generation

Purpose

Use AI to generate models and migrations from descriptions.

Prompt Pattern

Generate a Rails model and migration for:

Model: Product
Fields:
- name: string (required)
- sku: string (required, unique)
- description: text (optional)
- price: decimal (precision: 10, scale: 2)
- category: references (Category)
- active: boolean (default: true)

Validations:
- name must be present.
- sku must be present and unique.
- price must be greater than 0.

Associations:
- belongs_to :category
- has_many :order_items

Also generate the factory and model spec.

API Endpoint Development

Purpose

Use AI to generate API endpoints with request specs.

Prompt Pattern

Generate a Rails API controller and routes for:

Resource: Products (API::V1::ProductsController)
Actions: index, show, create, update, destroy

Requirements:
- index supports pagination (page, per_page).
- index supports filtering by category_id.
- show returns a single product with category name included.
- create requires authentication.
- Responses use JSON format with the following structure:
  { data: { id:, type:, attributes: {} }, errors: [] }

Also generate the request specs.

Test Generation

Purpose

Use AI to generate tests for existing code.

Prompt Pattern

Write RSpec tests for this Rails service object:

```ruby
class InviteUser
  def initialize(team:, email:, inviter:)
    @team = team
    @email = email
    @inviter = inviter
  end

  def call
    user = User.find_or_create_by!(email: @email)
    membership = @team.memberships.create!(user: user, inviter: @inviter)
    UserMailer.invitation(membership).deliver_later
    membership
  rescue ActiveRecord::RecordInvalid => e
    raise InvitationError, e.message
  end
end

Include tests for:

• Successful invitation.
• Duplicate email handling.
• Invalid team.
• Mailer delivery.

## Debugging

### Purpose

Use AI to diagnose Rails errors.

#### Prompt Pattern

I am getting this error in my Rails application:

[error message and stack trace]

Code context:

[relevant code]

Rails version: [version] Ruby version: [version]

What is the most likely cause and how should I fix it?

## Refactoring

### Purpose

Use AI to suggest Rails-specific refactorings.

#### Prompt Pattern

Help me refactor this Rails controller:

class OrdersController < ApplicationController
  def create
    @order = Order.new(order_params)
    @order.user = current_user
    @order.status = "pending"

    if @order.save
      InventoryService.deduct_stock(@order)
      PaymentService.charge(@order)
      OrderMailer.confirmation(@order).deliver_later
      redirect_to @order, notice: "Order created."
    else
      render :new, status: :unprocessable_entity
    end
  end
end

Goals:

• Extract business logic into a service object.
• Keep error handling consistent.
• Improve testability.

# Anti-patterns

## Rails-Specific Blind Spots

AI may suggest patterns that are not idiomatic Rails or that ignore
Rails conventions. Always verify that AI suggestions follow Rails
conventions.

## Over-Abstraction

AI may suggest extracting classes and modules where a simpler Rails
approach would suffice. Prefer Rails conventions unless there is a
clear reason to deviate.

## Ignoring Performance

AI-generated queries may introduce N+1 problems or inefficient
queries. Always review generated database access code.

# Related Documents

- [Rails Engineering Handbook](../handbooks/rails/)
- [Service Objects Guide](../guides/rails/service-objects/)
- [Testing Rails Applications Guide](../guides/rails/testing/)
- [Rails Upgrade Playbook](../playbooks/rails/upgrade/)
- [AI Workflows for Engineering](../prompts/engineering-ai-workflows/)