31021a8c85
This PR adds the ability to 1) connect to multiple databases in a model,
and 2) switch between those connections using a block.
To connect a model to a set of databases for writing and reading use
the following API. This API supercedes `establish_connection`. The
`writing` and `reading` keys represent handler / role names and
`animals` and `animals_replica` represents the database key to look up
the configuration hash from.
```
class AnimalsBase < ApplicationRecord
connects_to database: { writing: :animals, reading: :animals_replica }
end
```
Inside the application - outside the model declaration - we can switch
connections with a block call to `connected_to`.
If we want to connect to a db that isn't default (ie readonly_slow) we
can connect like this:
Outside the model we may want to connect to a new database (one that is
not in the default writing/reading set) - for example a slow replica for
making slow queries. To do this we have the `connected_to` method that
takes a `database` hash that matches the signature of `connects_to`. The
`connected_to` method also takes a block.
```
AcitveRecord::Base.connected_to(database: { slow_readonly: :primary_replica_slow }) do
ModelInPrimary.do_something_thats_slow
end
```
For models that are already loaded and connections that are already
connected, `connected_to` doesn't need to pass in a `database` because
you may want to run queries against multiple databases using a specific
role/handler.
In this case `connected_to` can take a `role` and use that to swap on
the connection passed. This simplies queries - and matches how we do it
in GitHub. Once you're connected to the database you don't need to
re-connect, we assume the connection is in the pool and simply pass the
handler we'd like to swap on.
```
ActiveRecord::Base.connected_to(role: :reading) do
Dog.read_something_from_dog
ModelInPrimary.do_something_from_model_in_primary
end
```
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| actioncable | ||
| actionmailer | ||
| actionpack | ||
| actionview | ||
| activejob | ||
| activemodel | ||
| activerecord | ||
| activestorage | ||
| activesupport | ||
| ci | ||
| guides | ||
| railties | ||
| tasks | ||
| tools | ||
| .codeclimate.yml | ||
| .gitattributes | ||
| .gitignore | ||
| .rubocop.yml | ||
| .travis.yml | ||
| .yardopts | ||
| .yarnrc | ||
| Brewfile | ||
| CODE_OF_CONDUCT.md | ||
| CONTRIBUTING.md | ||
| Gemfile | ||
| Gemfile.lock | ||
| MIT-LICENSE | ||
| package.json | ||
| rails.gemspec | ||
| RAILS_VERSION | ||
| Rakefile | ||
| README.md | ||
| RELEASING_RAILS.md | ||
| version.rb | ||
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.