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The copy here is of course up for discussion but it feels like we need to address the issue of old migrations in the Migration guide because other than mentioning the canonical nature of schema.rb/structure.sql or the actual database compared to migration files, it seems like more guidance would help. Here's a sample of the kinds of question people seem to often ask about old Rails migrations: - https://stackoverflow.com/questions/20119391/delete-old-migrations-files-in-a-rails-app - https://www.reddit.com/r/rails/comments/4ayosd/compacting_migrations_files_or_delete_them/ - https://stackoverflow.com/questions/4248682/is-it-a-good-idea-to-purge-old-rails-migration-files - https://stackoverflow.com/questions/707013/is-it-a-good-idea-to-collapse-old-rails-migrations - https://stackoverflow.com/questions/1981777/rails-remove-old-models-with-migrations - https://stackoverflow.com/questions/3343534/rebase-rails-migrations-in-a-long-running-project The common theme seems to be: "I've got old migrations, should I keep them around on an old project?". My personal stance is that as long as migrations run and don't take too long do so, you should keep them around since it allows people working on the Rails project with you to seamlessly upgrade their local development database without having to do a `db:drop db:schema:load` and lose all their seed data. While writing down this suggested new section it felt like I was describing a very cumbersome process that could be address with a rake task like: ```bash rails db:migrate:remove VERSION=20121201123456 ``` It rollback to the version just before `20121201123456`, delete the migration file, and run `db:migrate` to get back to the latest migration. This of course doesn't address a situation when someone would want to delete or merge all migrations prior to a certain date, which is addressed by [squasher](https://github.com/jalkoby/squasher). I'm not sure this is something we want to encourage people to do. Although I feel like with more and more production Rails apps over 5-years old, it's definitely a concern we should address. |
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Welcome to Rails
What's 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: Model, View, and Controller, each with a specific responsibility.
Model layer
The Model layer represents the domain model (such as Account, Product,
Person, Post, etc.) and encapsulates the business logic 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.
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.
Controller layer
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.
View layer
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.
Frameworks and libraries
Active Record, Active Model, Action Pack, and Action View can each be used independently outside Rails. In addition to that, Rails also comes with Action Mailer, a library to generate and send emails; Active Job, a framework for declaring jobs and making them run on a variety of queueing backends; Action Cable, a framework to integrate WebSockets with a Rails application; Active Storage, a library to attach cloud and local files to Rails applications; and Active Support, 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. -
Go to
http://localhost:3000and you'll see: "Yay! You’re 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!
Trying to report a possible security vulnerability in Rails? Please check out our security policy for guidelines about how to proceed.
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.