b24bfcce77
In an application that has a primary and replica database the data inserted on the primary connection will not be able to be read by the replica connection. In a test like this: ``` test "creating a home and then reading it" do home = Home.create!(owner: "eileencodes") ActiveRecord::Base.connected_to(role: :default) do assert_equal 3, Home.count end ActiveRecord::Base.connected_to(role: :readonly) do assert_equal 3, Home.count end end ``` The home inserted in the beginning of the test can't be read by the replica database because when the test is started a transasction is opened byy `setup_fixtures`. That transaction remains open for the remainder of the test until we are done and run `teardown_fixtures`. Because the data isn't actually committed to the database the replica database cannot see the data insertion. I considered a couple ways to fix this. I could have written a database cleaner like class that would allow the data to be committed and then clean up that data afterwards. But database cleaners can make the database slow and the point of the fixtures is to be fast. In GitHub we solve this by sharing the connection pool for the replicas with the primary (writing) connection. This is a bit hacky but it works. Additionally since we define `replica? || preventing_writes?` as the code that blocks writes to the database this will still prevent writing on the replica / readonly connection. So we get all the behavior of multiple connections for the same database without slowing down the database. In this PR the code loops through the handlers. If the handler doesn't match the default handler then it retrieves the connection pool from the default / writing handler and assigns the reading handler's connections to that pool. Then in enlist_fixture_connections it maps all the connections for the default handler because all the connections are now available on that handler so we don't need to loop through them again. The test uses a temporary connection pool so we can test this with sqlite3_mem. This adapter doesn't behave the same as the others and after looking over how the query cache test works I think this is the most correct. The issues comes when calling `connects_to` because that establishes new connections and confuses the sqlite3_mem adapter. I'm not entirely sure why but I wanted to make sure we tested all adapters for this change and I checked that it wasn't the shared connection code that was causing issues - it was the `connects_to` code. |
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yarn.lock |
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 queuing 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 myapp
where "myapp" is the application name.
-
Change directory to
myapp
and start the web server:$ cd myapp $ rails server
Run with
--help
or-h
for options. -
Go to
http://localhost:3000
and 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.