c2d33c4abf
Closes #21922
Let `Book(id, author_id)`, `Photo(id, book_id, author_id)` and `Author(id)`
Running `Book.group(:author_id).joins(:photos).count` will produce:
* Rails 4.2 - conflicts `author_id` in both projection and group by:
```sql
SELECT COUNT(*) AS count_all, author_id AS author_id
FROM "books" INNER JOIN "photos" ON "photos"."book_id" = "books"."id"
GROUP BY author_id
```
* Master (
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| actionmailer | ||
| actionpack | ||
| actionview | ||
| activejob | ||
| activemodel | ||
| activerecord | ||
| activesupport | ||
| ci | ||
| guides | ||
| railties | ||
| tasks | ||
| tools | ||
| .gitignore | ||
| .travis.yml | ||
| .yardopts | ||
| CODE_OF_CONDUCT.md | ||
| CONTRIBUTING.md | ||
| Gemfile | ||
| Gemfile.lock | ||
| load_paths.rb | ||
| rails.gemspec | ||
| RAILS_VERSION | ||
| Rakefile | ||
| README.md | ||
| RELEASING_RAILS.md | ||
| version.rb | ||
Welcome to Rails
Rails is a web-application framework that includes everything needed to create database-backed web applications according to the Model-View-Controller (MVC) pattern.
Understanding the MVC pattern is key to understanding Rails. MVC divides your application into three layers, each with a specific responsibility.
The Model layer represents your domain model (such as Account, Product,
Person, Post, etc.) and encapsulates the business logic that is specific to
your application. In Rails, database-backed model classes are derived from
ActiveRecord::Base. Active Record allows you to present the data from
database rows as objects and embellish these data objects with business logic
methods. You can read more about Active Record in its README.
Although most Rails models are backed by a database, models can also be ordinary
Ruby classes, or Ruby classes that implement a set of interfaces as provided by
the Active Model module. You can read more about Active Model in its README.
The Controller layer is responsible for handling incoming HTTP requests and
providing a suitable response. Usually this means returning HTML, but Rails controllers
can also generate XML, JSON, PDFs, mobile-specific views, and more. Controllers load and
manipulate models, and render view templates in order to generate the appropriate HTTP response.
In Rails, incoming requests are routed by Action Dispatch to an appropriate controller, and
controller classes are derived from ActionController::Base. Action Dispatch and Action Controller
are bundled together in Action Pack. You can read more about Action Pack in its
README.
The View layer is composed of "templates" that are responsible for providing appropriate representations of your application's resources. Templates can come in a variety of formats, but most view templates are HTML with embedded Ruby code (ERB files). Views are typically rendered to generate a controller response, or to generate the body of an email. In Rails, View generation is handled by Action View. You can read more about Action View in its README.
Active Record, Active Model, Action Pack, and Action View can each be used independently outside Rails. In addition to them, Rails also comes with Action Mailer (README), a library to generate and send emails; Active Job (README), a framework for declaring jobs and making them run on a variety of queueing backends; and Active Support (README), a collection of utility classes and standard library extensions that are useful for Rails, and may also be used independently outside Rails.
Getting Started
-
Install Rails at the command prompt if you haven't yet:
gem install rails -
At the command prompt, create a new Rails application:
rails new myappwhere "myapp" is the application name.
-
Change directory to
myappand start the web server:cd myapp rails serverRun with
--helpor-hfor options. -
Using a browser, go to
http://localhost:3000and you'll see: "Welcome aboard: You're riding Ruby on Rails!" -
Follow the guidelines to start developing your application. You may find the following resources handy:
Contributing
We encourage you to contribute to Ruby on Rails! Please check out the Contributing to Ruby on Rails guide for guidelines about how to proceed. Join us!
Everyone interacting in Rails and its sub-projects' codebases, issue trackers, chat rooms, and mailing lists is expected to follow the Rails code of conduct.
Code Status
License
Ruby on Rails is released under the MIT License.