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From Ruby on Rails to Nexy

In Nexy a Rails route and its controller action become one file under src/routes/: ERB views become .nexy pages with Jinja2, strong parameters become Pydantic models, and before_action becomes a dependencies.py.

Each section below shows a Rails habit, then the same thing in Nexy.

A route and its action

config/routes.rb

get "/api/hello", to: "hello#show"

app/controllers/hello_controller.rb

class HelloController < ApplicationController  def show    render json: { message: "Hello" }  endend

There is no routes.rb: the file path is the URL, the function name is the HTTP method.

src/routes/api/hello.py

async def GET():    return {"message": "Hello"}

`resources`

config/routes.rb

resources :notes, only: [:index, :create, :show, :destroy]

The seven REST actions are spread over two files, one per URL:

src/routes/api/notes/index.py

from pydantic import BaseModel NOTES: dict[int, str] = {}  class NewNote(BaseModel):    title: str  async def GET():    return [{"id": id, "title": title} for id, title in NOTES.items()]  async def POST(note: NewNote):    id = max(NOTES, default=0) + 1    NOTES[id] = note.title    return {"id": id, "title": note.title}

src/routes/api/notes/[id].py

from nexy.http import HTTPException from .index import NOTES  async def GET(id: int):    if id not in NOTES:        raise HTTPException(status_code=404, detail="No such note")    return {"id": id, "title": NOTES[id]}  async def DELETE(id: int):    NOTES.pop(id, None)    return {"deleted": id}

Rails action	Nexy
`index`, `create`	`GET`, `POST` in `notes/index.py`
`show`, `update`, `destroy`	`GET`, `PATCH`, `DELETE` in `notes/[id].py`
`new`, `edit`	`.nexy` pages, `notes/new.nexy` and `notes/[id]/edit.nexy`

`params` and strong parameters

app/controllers/items_controller.rb

def create  item = params.require(:item).permit(:name, :price)  render json: item, status: :createdend

The model is the permit list and the validation: unknown fields are dropped, wrong ones answer 422.

src/routes/api/items.py

from pydantic import BaseModel, Field from nexy.http import JSONResponse  class NewItem(BaseModel):    name: str    price: float = Field(gt=0)  async def POST(item: NewItem):    return JSONResponse(item.model_dump(), status_code=201)

A query string parameter, params[:q], is a function parameter:

src/routes/api/search.py

async def GET(q: str = "", page: int = 1):    return {"q": q, "page": page}

`namespace` and `before_action`

config/routes.rb

namespace :admin do  get "stats", to: "stats#show"end

app/controllers/admin/base_controller.rb

class Admin::BaseController < ApplicationController  before_action :require_admin   private   def require_admin    head :forbidden unless request.headers["X-Role"] == "admin"  endend

The namespace is the folder, and its dependencies.py is the before_action of every route in it:

src/routes/admin/stats.py

async def GET():    return {"users": 3}

src/routes/admin/dependencies.py

from nexy.http import Header, HTTPException  def require_admin(x_role: str = Header("")) -> None:    if x_role != "admin":        raise HTTPException(status_code=403, detail="Admins only")  dependencies = [require_admin]

`after_action` and Rack middleware

app/controllers/application_controller.rb

after_action { response.set_header("X-App", "demo") }

src/routes/middleware.py

from nexy.http import Request  async def middleware(request: Request, call_next):    response = await call_next(request)    response.headers["x-app"] = "demo"    return response

ERB views

app/controllers/users_controller.rb

def index  @users = [{ name: "Ada" }, { name: "Alan" }]end

app/views/users/index.html.erb

<ul>  <% @users.each do |user| %>  <li><%= user[:name] %></li>  <% end %></ul>

The action and the view are one .nexy file; instance variables become plain names:

src/routes/users.nexy

---users = [{"name": "Ada"}, {"name": "Alan"}]---<ul>  {% for user in users %}  <li>{{ user.name }}</li>  {% endfor %}</ul>

<%= %> escapes and {{ }} does not: escape what a visitor typed with {{ value | e }}. <%== %> and raw are | safe.

Layouts and `yield`

app/views/layouts/application.html.erb

<!DOCTYPE html><html>  <body><%= yield %></body></html>

src/routes/layout.nexy

---children: prop[NexyElement]---<!DOCTYPE html><html>  <body>{{ children | safe }}</body></html>

A layout.nexy in a subfolder nests inside this one, as a layout per controller does.

Partials

app/views/shared/_card.html.erb

<article><h2><%= title %></h2><%= yield %></article>

<%= render "shared/card", title: "Latest" do %><p>This week</p><% end %>

src/components/Card.nexy

---title: prop[str]---<article>  <h2>{{ title }}</h2>  <Slot /></article>

src/routes/index.nexy

---from "@/components/Card.nexy" import Card---<Card title="Latest">  <p>This week</p></Card>

@ is src/: nx new writes useAliases = {"@": "src"} in nexyconfig.py.

`form_with` and `redirect_to`

app/views/notes/index.html.erb

<%= form_with url: notes_path do |form| %>  <%= form.text_field :title %>  <%= form.submit "Add" %><% end %>

app/controllers/notes_controller.rb

def create  Note.create!(title: params[:title])  redirect_to notes_pathend

An action is the create the form posts to. Its parameters are the fields, and the visitor is redirected back to the page with a 303:

src/actions/notes.py

from nexy.decorators import Action TITLES: list[str] = []  @Actionasync def add_note(title: str) -> None:    TITLES.append(title)

src/routes/notes.nexy

---from src.actions.notes import TITLES---<form method="post" action="{{ __actions_path['add_note'] }}">  <input name="title">  <button type="submit">Add</button></form><ul>  {% for title in TITLES %}  <li>{{ title }}</li>  {% endfor %}</ul>

Active Record and migrations

app/models/post.rb

class Post < ApplicationRecord  scope :published, -> { where(published: true) }end

Nexy has no ORM of its own; nx new can scaffold SQLModel, SQLAlchemy or Tortoise-ORM. With SQLModel:

src/models/post_model.py

from sqlmodel import Field, SQLModel  class Post(SQLModel, table=True):    id: int | None = Field(default=None, primary_key=True)    title: str    published: bool = False

src/routes/api/posts/published.py

from sqlmodel import Session, select from src.configs.db import enginefrom src.models.post_model import Post  async def GET():    with Session(engine) as session:        posts = session.exec(select(Post).where(Post.published)).all()    return {"titles": [post.title for post in posts]}

Rails	Nexy
`rails generate migration AddPosts`	`nx migrate -m "add posts"`
`rails db:migrate`	`nx migrate --upgrade`

`ActiveRecord::RecordNotFound` and `public/404.html`

app/controllers/posts_controller.rb

def show  @post = POSTS.fetch(params[:slug]) { raise ActiveRecord::RecordNotFound }end

src/routes/posts/[slug].nexy

---from nexy import notFound POSTS = {"hello": "Hello, world"} slug: prop[str]if slug not in POSTS:    notFound()---<h1>{{ POSTS[slug] }}</h1>

notfound.nexy at the routes root is public/404.html, rendered like any page:

src/routes/notfound.nexy

<h1>Not found</h1>

Sessions

app/controllers/sessions_controller.rb

def create  session[:user] = params[:name]  render json: { user: session[:user] }end

nexyconfig.py

from nexy.core.models import NexyConfigModel  class NexyConfig(NexyConfigModel):    useAliases = {"@": "src"}    useSession = {"secret_key": "change-me"}

src/routes/api/login.py

from pydantic import BaseModel from nexy.http import Request  class Login(BaseModel):    name: str  async def POST(request: Request, body: Login):    request.session["user"] = body.name    return {"user": body.name}

A page reads it with useSession().

Caching

app/controllers/blog_controller.rb

def index  expires_in 1.minute, public: trueend

src/routes/blog/index.nexy

---revalidate = 60---<h1>Blog</h1>

Active Job

app/controllers/signups_controller.rb

WelcomeMailerJob.perform_later(params[:email])head :accepted

src/routes/api/signup.py

from nexy.http import BackgroundTasks, JSONResponse  def send_welcome(email: str) -> None: ...  async def POST(email: str, tasks: BackgroundTasks):    tasks.add_task(send_welcome, email)    return JSONResponse({"queued": True}, status_code=202)

For retries and separate workers, as with Sidekiq, use Celery, RQ or arq.

Action Cable

app/channels/echo_channel.rb

class EchoChannel < ApplicationCable::Channel  def receive(data)    transmit(data)  endend

src/routes/ws/echo.py

from fastapi import WebSocket  async def SOCKET(websocket: WebSocket):    await websocket.accept()    await websocket.send_text(await websocket.receive_text())

Hotwire

Turbo Drive's page swaps match the client router of a client-mode project, and Stimulus controllers match islands: a small component that hydrates inside a server page. See Islands and CSR.

Tests

spec/requests/hello_spec.rb

RSpec.describe "Hello", type: :request do  it "says hello" do    get "/api/hello"    expect(response.parsed_body).to eq("message" => "Hello")  endend

tests/test_hello.py

from fastapi.testclient import TestClient from nexy.app import app  def test_hello():    assert TestClient(app).get("/api/hello").json() == {"message": "Hello"}

Running

Rails	Nexy
`rails new`	`nx new`
`bin/rails server`	`nx dev`
`bin/rails routes`	`/docs`
`RAILS_ENV=production bin/rails server`	`nx build`, then `nx start`
`bin/rails test` / `rspec`	`nx test`

Next steps

Edit on GitHub

From Ruby on Rails to Nexy

A route and its action

resources

params and strong parameters

namespace and before_action

after_action and Rack middleware

ERB views

Layouts and yield

Partials

form_with and redirect_to

Active Record and migrations

ActiveRecord::RecordNotFound and public/404.html

Sessions

Caching

Active Job

Action Cable

Hotwire

Tests

Running

Next steps

`resources`

`params` and strong parameters

`namespace` and `before_action`

`after_action` and Rack middleware

Layouts and `yield`

`form_with` and `redirect_to`

`ActiveRecord::RecordNotFound` and `public/404.html`