49b6b211a9
This PR proposes moving the schema cache from the connection to the pool so the connection can ask the pool for the cache. In a future PR our goal is to be able to read the yaml file from the pool so we can get rid of the `active_record.check_schema_cache_dump` initializer. This will fix the issues surrounding dumping the schema cache and mulitple databases. Why do we want to get rid of the initializer you ask? Well I was looking at #34449 and trying to make it work for our usecase and it revealed A LOT of problems. There are a few issues that I will fix in remaining PRs with SchemaMigration, but there's a big glaring issue with this initializer. When you have an application with multiple databases we'll need to loop through all the configurations and set the schema cache on those connections. The problem is on initialization we only have one connection - the one for Ar::Base. This is fine in a single db application but not fine in multi-db. If we follow the pattern in #34449 and establish a connection to those other dbs we will end up setting the cache on the _connection object_ rather than on all connections that connect for that config. So even though we looped through the configs and assigned the cache the cache will not be set (or will be set wrong) once the app is booted because the connection objects after boot are _different_ than the connection objects we assigned the cache to. After trying many different ways to set the schema cache `@tenderlove` and I came to the conclusion that the initializer is problematic, as is setting the schema cache twice. This is part 1 to move the cache to the pool so the cache can read from the schema cache yaml file instead of setting it when initializing the app. To do this we have created a `NullPool` that initializes an empty cache. I put the `get_schema_cache` and `set_schema_cache` in an `AbstractPool` so we can share code between `ConnectionPool` and `NullPool` instead of duplicating code. Now we only need to set the schema_cache on the pool rather than the connection. In `discard!` we need to unset the connection from the schema_cache - we still want the cache just not the connection. |
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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; Action Mailbox, a library to receive emails within a Rails application; 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; Action Text, a library to handle rich text content; 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.