To allow HTTP 304 responses, Rails offers the fresh_when method for controllers.

The most common way is to pass an ActiveRecord instance or scope, and fresh_when will set fitting E-Tag and Last-Modified headers for you. For scopes, an extra query is sent to the database.

fresh_when @users

If you do not want that magic to happen, e.g. because your scope is expens...

For Rails models where only one of multiple attributes may be filled out at the same time, there is no built-in validation.

I've seen different solutions in the wild, each with different downsides:

• Private method referenced via validate: works, but is barely portable and clutters the model.
• Multiple presence validations with "if other is blank" each: looks pretty, but is incorrect as it allows both values to be filled in; also the error messages for a blank record are misleading.

Here is a third option: Write a custom validator to ...

When working with feature branches, stale branches pile up over time. It's best to remove them right after merge, locally and on the remote, but it is a little tedious: you need to remember it, and perform the few steps manually each time.

Enter Git hooks. The folks at Liquid Light have built a little post-merge hook that will delete a feature branch on confirmation....

Recently we detected a memory leak in one of our applications. Hunting it down, we found that the memory leak was located in Rails' #prepend_view_path. It occurs when the instance method prepend_view_path is called in each request, which is a common thing in a multi-tenant application.

On top of leaking memory, it also causes a performance hit, since templates rendered using the prepended view path will not be cached and compiled anew on each request.

This is not a new memory leak. It was [first reported in in 2014](https://github.com/...

SELECT pg_size_pretty(pg_database_size('some-database'));

Example

SELECT pg_size_pretty(pg_database_size('cards_p'));
----------------
 13 GB
(1 row)

SELECT pg_database_size('cards_p');
 pg_database_size 
------------------
      13524832927
(1 row)

Related

• PostgreSQL: Show size of all databases
• PostgreSQL: How to show table sizes

When paginating records, we usually need to know the number of total records in order to render pagination links. Popular pagination libraries like will_paginate or Kaminari do this for us by simply issuing an extra query, like this:

SELECT post.* FROM posts LIMIT 20 OFFSET 100;

SELECT COUNT(*) FROM posts;   

This is fine most of the time. But rarely, you might have very complicated WHERE conditions or a subquery that takes time to run. In thes...

It might sometimes be useful to check whether your Rails application accesses the file system unnecessarily, for example if your file system access is slow because it goes over the network.

The culprit might be a library like carrierwave that checks file existence or modification times, whereas your application could determine all this from your database.

Introducing strace

One option it to use strace for this, which logs all system calls performed by a process.

To do this, start your rails server using something like

DISA...

Testing file download links in an end-to-end test can be painful, especially with Selenium.

The attached download_helpers.rb provides a download_link method for your Capybara tests. It returns a hash describing the download's response:

details = download_link('Download report')
details[:disposition]  # => 'attachment' or 'inline'
details[:filename]     # => 'report.txt'
details[:text]         # => file content as string
details[:content_type] # => 'text/plain'

Features

Compared to [other approaches](...

There is a way to use multiple databases in Rails.
You may have asked yourself how you're able to keep your test databases clean, if you're running multiple databases with full read and write access at the same time. This is especially useful when migrating old/existing databases into a new(er) one.

Your database.yml may look like this:

default: &default
  adapter: postgresql
  encoding: unicode
  username: <%= ENV['DATABASE_USER'] %>
  host: <%= ENV['DATABASE...

tl;dr
You can use attribute? as shorthanded version of attribute.present?, except for numeric attributes and associations.

Technical Details

attribute? is generated for all attributes and not only for boolean attributes.

These methods are using #query_attribute under the hood. For more details you can see ActiveRecord::AttributeMethods::Query.

In most circumstances query_attribute is working like attribute.present?. If your attribute is responding to :zero? then you have to be aware that `query_attri...

You can use Unpoly's up.on with a named listener function and immediately unbind this event listener with { once: true }:

up.on('up:fragment:inserted', { once: true }, function () { ... })

In Unpoly 1 you can immediately unregister the listener with up.off:

up.on('up:fragment:inserted', function fragmentInsertedCallback() {
  up.off('up:fragment:inserted', fragmentInsertedCallback)
  // ... code for the callback function, which should run only once
})

Exam...

tl;dr: Use the URLSearchParams API to make your live easier if you want to get or manipulate query parameters (URL parameters).

URLSearchParams API

The URLSearchParams API is supported in all major browsers except IE 11.

It offers you a bunch of useful methods:

• URLSearchParams.append() - appends a query parameter
• URLSearchParams.delete() - deletes the specified query parameter
• URLSearchParams.get() - returns the value of the specified query parameter
• `URLSearchP...

Redis.current will be removed without replacement in redis-rb 5.0.
Version 4.6.0 adds deprecation warnings for Redis.current and Redis.current=:

`Redis.current=` is deprecated and will be removed in 5.0.

If your application still uses Redis.current, you can only fix it by no longer using it. Here is how.

Redis.new when you need it

You can easily instantiate a Redis client when you need it.

There is probably already a constant like REDIS_URL that you use to configure Sidekiq or similar. So just use that one.

``...

RSpec's let allows you to super into "outside" definitions, in parent contexts.

Example:

describe '#save' do
  subject { described_class.new(attributes) }
  let(:attributes) { title: 'Example', user: create(:user) }

  it 'saves' do
    expect(subject.save).to eq(true)
  end

  context 'when trying to set a disallowed title' do
    let(:attributes) { super().merge(title: 'Hello') } # <==

    it 'will not save' do
      expect(subject.save).to eq(false)
    end
  end
end

I suggest you don't make a habit of using this regula...

Sometimes we write plain SQL queries in migrations so we don't have to mock ActiveRecord classes. These two migrations do the same:

class Migration1 < ActiveRecord::Migration[5.2]
  class User < ActiveRecord::Base; end

  def up
    add_column :users, :trashed, :boolean
    
    User.update_all(trashed: false)
  end
end

class Migration2 < ActiveRecord::Migration[5.2]
  def up
    add_column :users, :trashed, :boolean

    update("UPDATE users SET trashed = #{quoted_false}")
  end
end

The plain SQL migration is less code, but h...

Since Rails 6.1, if we use where.not with multiple attributes, it applies logical NAND (NOT(A) OR NOT(B)) instead of NOR (NOT(A) AND NOT(B)). If you do not take care, this change will increase the matched set.

Examples

"Don't send newsletters neither to admins nor to trashed users!" becomes "Don't send newsletters to trashed admins".

User.where.not(role: 'admin', trashed: true)
# Before Rails 6.1, with NOR
=> "SELECT "users".* FROM "users" WHERE "users"."role" != 'admin' AND "users"."trashed" != TRUE"
# Equivale...

Proxy caching is a good feature to serve your publicly visible application content faster and reduce load on your servers. It is e.g. available in nginx, but also affects proxies delivered by ISPs.

Unfortunately, there is a little problem in Rails < 6.1 when delivering responses for different MIME-types. Say you have an arbitrary route in your Rails application that is able to respond with regular HTML and JSON. By sending the specific MIME type in the Accept header, you tell the application to either return HTML (text/html) or JSON (`t...

Field error steps

Spreewald's The ... field should have an error and The ... field should have the error ... steps now have built-in support for Rails and Bootstrap (v3-v5) error classes. When using Bootstrap, it is no longer necessary to overwrite the steps in your project.

At the same time, support for formtastic has been removed as there were no real use cases. Due to that, no breaking change was introduced, as the amount of users affected by this should be zero (it was neither in the documentation nor tested).

Users may now add...

The Interactive Advertising Bureau (IAB) is a European marketing association which has introduced a standard how advertising can be served to users in line with the General Data Protection Regulation (GDPR). This standard is called the TCF 2.0 (Transparency and Consent Framework). If you want to integrate any kind of advertising into a website, chances are the advertising network will require your website to implement that standard. This is a very brief overview of what this means:

The basic idea in the TCF 2.0 ...