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Co-authored-by: Wojciech Wnętrzak <[email protected]>

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Co-authored-by: Wojciech Wnętrzak <[email protected]>

Author: vipulnsward

_posts/2025-04-04-this-week-in-rails.markdown

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+---
+layout: post
+title: "must-understand, with_default_isolation_level, Rails World CFP and more!"
+categories: news
+author: vipulnsward
+og_image: assets/images/this-week-in-rails.png
+published: true
+date: 2025-04-04
+---
+
+Hi, it's [Vipul](https://www.saeloun.com/team/vipul). Let's explore this week's changes in the Rails codebase.
+
+[Last Week for Rails World 2025 Call for Papers](https://rubyonrails.org/2025/3/7/apply-to-speak-at-rails-world-2025)  
+This is the last week for The CFP for Rails World 2025! 
+
+[Submit your talk until April 10th.](https://sessionize.com/rails-world-2025/)
+
+[Add must-understand directive according to RFC 9111](https://github.com/rails/rails/pull/54833)  
+The `must-understand` directive indicates that a cache must understand the semantics of the response status code, or discard the response. This directive is enforced to be used only with `no-store` to ensure proper cache behavior.
+
+```ruby
+class ArticlesController < ApplicationController
+  def show
+    @article = Article.find(params[:id])
+    if @article.special_format?
+      must_understand
+      render status: 203 # Non-Authoritative Information
+    else
+      fresh_when @article
+    end
+  end
+end
+```
+
+[Use UNLINK for RedisCacheStore in ActiveSupport](https://github.com/rails/rails/pull/54861)  
+The `RedisCacheStore` now uses Redis's `UNLINK` command instead of `DEL` for cache entry deletion, enabling asynchronous and non-blocking removal of keys, which enhances performance.
+
+[Add `Cache#read_counter` and `Cache#write_counter`](https://github.com/rails/rails/pull/54855)  
+This introduces 2 new methods on `Rails.cache`: `read_counter` and `write_counter`, to read values that are being incremented/decremented.
+
+```ruby
+Rails.cache.write_counter("foo", 1)
+Rails.cache.read_counter("foo") # => 1
+Rails.cache.increment("foo")
+Rails.cache.read_counter("foo") # => 2
+```
+
+[Change redirect status code in SessionsController#destroy template from 302 to 303](https://github.com/rails/rails/pull/54849)  
+The new Authentication generator introduced in Rails 8.0, creates a `SessionsController` that returns a 302 Redirect response in its destroy action.
+With this change it will now issue a 303(See Other) status code instead of 302(Found) when redirecting after logout, to comply with the [9110 spec](https://www.rfc-editor.org/rfc/rfc9110#status.302)
+
+[Include cookie name in length calculation](https://github.com/rails/rails/pull/54843)  
+This change updates Rails to include the cookie name's length when validating that a cookie stays within the 4KB limit, 
+aligning its behavior with browser standards.
+
+[Introduce with_default_isolation_level in ActiveRecord](https://github.com/rails/rails/pull/54836)  
+This change introduces the `with_default_isolation_level` method in ActiveRecord, allowing to set a default database isolation level for specific code blocks.
+This is particularly useful when migrating large applications to a new isolation level, as it enables enforcing the desired level in targeted areas, such as base controllers, facilitating smoother transitions and ensuring consistent transaction behavior.
+
+```ruby
+class ApiV2Controller < ApplicationController
+  around_action :set_isolation_level
+
+  def set_isolation_level
+    Product.with_default_isolation_level(:read_committed) do
+      yield
+    end
+  end
+end
+# forces all controllers that subclass from ApiV2Controller to start getting new isolation level
+```
+
+[With postgres adapter, prepend `structure_load_flags` instead of appending them](https://github.com/rails/rails/pull/54813)
+When using postgres adapter and the `structure_load_flags` options, the extra flags were appended instead of prepended to the default ones, causing the `psql` command to ignore some of the extra flags.
+Now, the default arguments `args` are appended to the `extra_flags` instead of the opposite.
+
+_You can view the whole list of changes [here](https://github.com/rails/rails/compare/@%7B2025-03-29%7D...main@%7B2025-04-04%7D)._  
+_We had [15 contributors](https://contributors.rubyonrails.org/contributors/in-time-window/20250329-20250404) to the Rails codebase this past week!_  
+
+Until next time!
+
+_[Subscribe](https://world.hey.com/this.week.in.rails) to get these updates mailed to you._